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R e s p i r a t i o n P h y s i o l o g y I 1 8 ( 1 9 9 9 ) 1 0 3 I l 5
wr','u'.elsevier.com locate resphysiol
The energetics
of anaerobic muscle metabolism: a
reappraisal of older and recent conceptso
Pietro Enrico di Prampero ", Guido Ferretti
b'*
,, Dipttrtimertro cli Scicn:e e Tccnologie Biomedicha. Lnirarsitt) tli Lttlinc. Piu::ula Kolbe 1. I-33100 (itlitra. Itul.t'
b Dët;(trtetn(nt dc Ph)',:iologie, Centre Méttirl L.init'ar.siruira. I rut' Micht'l St'r't't'/. CH-l2ll Genèt'c 1, Swit:crlutnl
Accepted 24 Ar-rgust 1999
Abstract
This paper ciiscusses under an energetic perspective the recent and older evidence supportin-u the classical notiott t h a t t h e ' o x y g e n 6 e b t ' , a s o r i g i n a l l y < l e f i n e c i b y M a r g a r i a e t a l . ( 1 9 3 3 ) [ A m . J . P h y s i o l . 1 0 6 . 6 8 9 7 1 4 ] . c o n s i s t s o 1 ' t w o major components: the alactic oxygen clebt. with a half-time of the order of 30 sec. and the lactic oxygen debt. with a much longer half-time, similar to that of lactic acid removal from blood etfier exercise ( : 15 min). In particular, two ensuing concepts are treated, namely (i) the energetic eqr,rivalent of blood lactate accumulation in blood. whence the notions of lactic power ancl lactic capacity. and (ii) the energy sources allowing contretction of the oxygen deficit at the onset of square-wave exercise. The notion of alactic oxygen cleficit is rediscussed on the basis ol- recent evidence in humans. The analogies between lactate accumulation during supramaximal exercise and during exercise transients are discussed under an energetic perspective. O 1999 Elsevier Science B.V. All rights reserved.
Keyx.grls: Exercise, energctics: Lactic acid. removal; Lactic acid. energy eqr.rivalent: Mammals. hunlaus; Muscle. skeletal. lactic acid: Oxvsen. debt
l. Introduction
The aim of this paper is to review briefly about 40 years of a main chapter of the history of the energetics of muscular exercise. namely that of the
" Dedicated to Professor Paolo Cerretelli on the occasion of his retirement fiom a chair of physiology at the University of G e n e v a . S w i t z e r l a n d .
* Corresponding author. Tel.: f 4l-22-702-5363; f a x : + 4 l
-22-702-5402.
E -nrui I atltlre,s.s : guido.ferretti(itmedecine.unige.ch (G.
Fer-retti )
0 0 3 , 1 - 5 6 8 7 r 9 9 , S - see tiont matter e 1999 Elsevier Science B.V. All P I I : S 0 0 1 4 - 5 6 8 7 ( 9 9 ) 0 0 0 8 3 - 3
anaerobic energy sources. It seems fair to say from the outset that we will not try to present a
comprehensive review of the matters at stake. We
will rather focus on facts and theories generated by the 'school of Margaria' from the early sixties
onwards, not only because this paper is dedicated
to Paolo Cerretelli. who was and still is one of the
leaders among Rodolfo Margaria's heirs. but also
and especially because we are convinced that the concepts created by the School of Margaria, and summarized below, can provide a solid back-ground and a good starting point for many as yet
unanswered questions.
I0,1
I n 1 9 3 3 , a p a p e r e n t i t l e d ' T h e possible
mecha-nism of contracting and paying the oxyger-r debt
a n d t h e r o l e o f l a c t i c a c i d i n m u s c u l a r c o n t r a c -t i o n ' . w a s p u b l i s h e d in -t h e A m e r i c a n J o u r n a l o f P h y s i o l o g y (M a r g a r i a e t a l . . 1 9 3 3 ) . T h i s p a p e r " indeed a seminal one. introduced the concept of ' a l a c t i c
o x y g e n d e b t ' . a n d t o r t h i s v e r y r e a s o n i n i t i a t e d a r e v o l u t i o n in t h e p h y s i o l o g y o f m u s c l r -lar exercise. The 'phospha-9ens' had been recently iderrtified (Eg-eleton and Eggleton. 1927, Fiske a n d S u b b a r o w , 1 9 2 1 : L o h m a n n . 1 9 2 8 ) . a n d a n u m b e r o f e n s r - r i n g o b s e r v a t i o n s o n i s o l a t e d m u s -c l e -c o n t r a -c t i o n w a s -c a s t i n g a s h a d o w o v e r H i l l and Meyerhof"s theory of the energetics of muscle contraction (Hill. 1932:. fbr a review see Needham, l 9 7 l ) . A c c o r d i n g t o t h i s t h e o r y , f o r w h i c h H i l l and Meyerhof were awarded the Nobel Prize for M e d i c i n e o r P h y s i o l o g y in 1 9 2 3 , o x i d a t i o n o f glycogen to lactic acid is the main energy source f o r m u s c r - r l a r c o n t r a c t i o n , w h e r e a s o x y g e n is c o n -s u m e d fb r o x i d i -s i n g a f r a c t i o n o f t h e a c c u m u l a t e d lactic acid. so yielding the energy for the resynthe-sis to glycogen of the remaining fraction (Hill,
1 9 2 4 ) . M a r g a r i a e t a l . ( 1 9 3 3 ) . b y m e a n s o f a mathematical analysis of the oxygen consuûrption curve after heavy exercise in man" demonstrated that a substantial fraction of the oxygen debt payment is independent of lactic acid removal f r o m b l o o d . A s a c o n s e q u e n c e , t h e y s u b d i v i d e d the overall oxygen debt in two major components: t h e a l a c t i c o x y g e n d e b t . w i t h a s h o r t e r ti m e c o n -s t a n t t ( h a l f - t i m e . t r : : t I n 2 : 3 0 s e c ) . a n d t h e l a c t i c o x y g e n d e b t . w i t h a m u c h l o n g e r t, , . s i m i l a r to that of lactic acid removal from blood alter e x e r c i s e ( : l 5 m i n ) .
These findings generated a brilliant refutation of Hill and Meyerhofs theory. representing a major step fbrward on the way to our present understanding of the energetics of muscle contract i o n . M a r g a r i a e contract a l . ( 1 9 3 3 ) h a d s contract u d i e d contracth e k i n e contract -ics of the oxygen debt payment. The time had c o m e o f c h a l l e n g i n g M a r g a r i a ' s c o n c e p t o f o x y g e n debt by studying the way it was incurred at the onset of exercise. Apart from the isolated pioneer-i n g w o r k o f H e n r y ( 1 9 5 1 ) o n e x e r c pioneer-i s e t r a n s i e n t s . this task was essentially undertaken in the early s i x t i e s b y a g r o u p o f s c i e n t i s t s i n M i l a n o . a m o n g whom Cerretelli played a major role, under the intellectual leadership of Rodolfo Margaria.
R t , . s : l t i r t r t i r t n P h . r ' . s i o h t g . t ' 1 l 8 ( 1 9 9 9 ) l 0 - l 1 I 5 T h i s l e d t o t h e c r e a t i o n o f t w o b a s i c c o n c e p t s i n t h e e n e r g e t i c s o f m u s c u l a r e x e r c i s e : ( i ) t h e e n -e r g -e t i c -e q u i v a l -e n t o f b l o o d l a c t a t -e a c c u m u l a t i o n i n b l o o d . w h e n c e th e n o t i o n s o f l a c t i c p o w e r a n d l a c t i c c a p a c i t y . a n d ( i i ) t h e o b l i g a t o r y fr a c t i o n o f oxygen deficit at the onset of exercise. These c o n c e p t s a r e d i s c u s s e d . u n d e r a h i s t o r i c a l p e r s p e c -tive. in the present paper. The paper is therefbre d i v i d e d i n t w o s e c t i o n s . t h e f i r s t d e v o t e d t o a n a n a l y s i s o f t h e a n a e r o b i c l a c t i c e n e r g y s o u r c e s . t h e second to the enersetics of the oxvsen deficit and d e b t .
2. The anaerobic energy sources 2.1. Tltc cnerg.r ctluitulent of lut'tic ut'itl . f o r u u t t i o t t
M a r g a r i a e t a l . ( 1 9 6 3 a ) d e t e r m i n e d t h e e n e r g y c o s t o f r u n n i n g a i t v a r i o u s s p e e d s a n d i n c l i n e s o f t h e t e r r a i n " a l l o w i n g a n e s t i m a t e o f t h e c o r r e -s p o n d i n g m e t a b o l i c p o w e r r e q u i r e m e n t -s . S o t h e Milano -sroup set out to determine the rate of l a c t a t e a c c u m u l a t i o n in b l o o d a t s p e e d s a n d i n -clines requiring a n'retabolic power larger than t h a t c o r r e s p o n d i n g t o t h e s u b j e c t s ' m a x i m a l o x y -g e n c o n s r - r m p t i o n ( M a r g a r i a et al., 1963b). Each c o n s t a n t s u p r a m a x i m a l s p e e d t r i a l w a s s u b d i v i d e d i n t o s e v e r a l b o u t s o f i n c r e a s i n g d u r a t i o n , u n t i l v o l i t i o n a l e x h a u s t i o n . A f t e r e a c h b o u t . t h e s u b j e c t was asked to rest and the lactic acid concentration in blood measured throughout the recovery pe-r i o d . A s s u m i n g th a t ( i ) t h e p e a k c o n c e n t pe-r a t i o n o f l a c t i c a c i d . a t t a i n e d b e t w e e n t h e 5 t h a n d t h e B t h m i n o f r e c o v e r y , is e q u a l t h r o u g h o u t t h e b o d y f l u i d s , a n d ( i i ) t h e w a t e r f r a c t i o n s o f t h e b l o o d a n d o f t h e w h o l e b o d y a r e 0 . 8 a n d 0 . 6 r e s p e c -t i v e l y . i -t w a s p o s s i b l e t o e s t i m a t e t h e a m o u n t o f l a c t i c a c i d p r o d u c e d p e r k g o f b o d y m a s s . T h i s m a d e i t p o s s i b l e to d e m o n s t r a t e . a s b e l i e v e d a t t h o s e t i m e s . t h a t t h e r a t e a t w h i c h l a c t i c a c i d i s p r o d u c e d ( i n g k g I m i n I ) ( a c t u a l l y a c c u m u -lated, and on average, as we will see below)
increases linearly with the corresponding
m e t a b o l i c p o w e r ( i n k c a l k g I m i n ' ) ( F i g . l ) . T h e i n t e r c e p t o n t h e r a x i s o f t h i s l i n e w a s c o n -sidered indicative of the metabolic power below
P.E. di Prttrttparg. G. larrt'tti Rc.spirutigtr Pft.t'.siolog.t' 118 (1999) 10.1 115 I 0 5
which no net production of lactic acid occurs: indeed this intercept corresponded to the power at w h i c h t h e p l a t e a u d e f i n i n g th e s u b j e c t ' s m a x i m a l oxygen consllmption was attained. The slope of t h e l i n e w a s t a k e n a s a m e a s u r e o f t h e a m o u n t o f energy released in vivo by the production of I -u of l a c t i c a c i d : i t a m o u n t e d t o 2 2 2 c a l g ' (84 kJ m o l r 1 . T h i s o r i g i n a l r e s u l t w a s e s s e n t i a l l y c o n f i -rmed by further data from the same school on h u m a n s ( M a r g a r i a e t a l . . 1 9 J 1 , l 9 l 2 ) . r u n n i n g dogs (Cerretelli et al.. 1964), and isolated-perfused d o g g a s t r o c n e m i i ( C e r r e t e l l i e t a l . , 1 9 6 9 ) .
I n s p i t e o f t h e c o n s i s t e n c y o f t h e r e s u l t s " t h e n L l m e r o u s a s s u m p t i o n s u n d e r l y i n g t h e a b o v e c o n -c l u s i o n s s t i r r e d a h e a t e d d e b a t e , in p a r t b e -c a u s e some of them were either implicit or definitely unsound. in part because of preconceived. if rlot
altogether wrong. ideas on the energetic signifi-c a n signifi-c e o f l a signifi-c t i signifi-c a signifi-c i d p r o d u signifi-c t i o n . T h i s s t a t e o f afJairs was most unfbrtunate. because it precluded a w i d e s p r e a d p r a c t i c a l u s e o f t h e ' e n e r g y e q t r i v a -l e n t o f -l a c t a t e fb r n ' r a t i o n i n v i v o ' . t h u s i n t h e e n d hin<lering the pro-eress of our knowledge in the f i e l d . I n d e e d w e m a i n t a i n t h a t . a s o f t e n p o i n t e d o u t e v e r s i n c e . t h e a b o v e c a l c u l a t e d e n e r g y e q u i v a l e n t . a l b e i t w i t h s o m e c a u t i o n s a n d l e s s e m p h a -sis, is an extremely usef ul practical tool fbr e s t i m a t i n g t h e w l i o l e b o d y e n e r g y e x p e n d i t u r e cluring supramttximal effbrts (fbr a review see di P r a m p e r o , l9 8 l ) . T h e l a s t s t a t e m e n t i s d e v e l o p e d i n t h e n e x t p a r a g r a p h s " w h e r e w e w i l l f i r s t e n u -merate and cliscuss the several assurt-tptions under-l y i n g t h i s c o n c e p t , a n d t h e n r e p o r t r e c e n t a n d o l d e r e v i d e n c e i n i t s s u p p o r t .
3*:__
lrg.rnin 6orI
Ii
501- 401-I i i I I i I 301-I I I I I I I I 20L crlqfËt hg.min c l l 1 . kg.min 200 150r.oo
9 e " kg-rt" o . 7 5 o.50 100 o.25 150 200 250 300 350 400 c r l n c t t r / k g ' m i nF i g . l . I n c r c a s e o f l a c t a t e in t h c b o c l y i n - u k g I rnin I lright ordinate). and nct stcady-state O . c o n s u r . n p t i o n p e r u n i t o f b o d y w c i g h t ( l e l i o r c l i n a t e ) . t t s a l t r n c t i o r - r o f ' t h e i n t e n s i t l ' o 1 ' e x c r c i s e e r p r e s s c d i n c a l k - s I min r. Non-athletes. f'Lrll l i n c : a t h l e t e . b r o k e n l i n e . T h c f ' u l l l i n e l b r l a c t a t e c r o s s e s t h e a b s c i s s a a t 2 2 0 c a l k g I min r. about the same value at which the corresponcling O . c o n s u m p t i o n li n e r e a c h e s i t s m a x i m u m . B e l o w t h i s l e v e l . n o l a c t a t e is p r o d L r c e d a n d t l t c w o r k i s c a r r i c d o u t a e r o b i c a l l y ' . T h e l a c t a t e l i n e f o r a t h l e t c s is c l i s p l a c e d t o t h e r i - u h t . i n c l i c a t i n g a h i g h c r c a p a c i t y ' l b r a e r o b i c r v o r k a n d a h i g h e r m a x i m a l o x y g e n c o r l s u m p t r o l l . T h e s l o p c 9 f t h c t w o l a c t a t e li n e s is t h e s a m e a n c l in c l i c a t e s a n e n e r g y ' ' p r o c l u c t i o n ' o f a b o u t 2 2 2 c a l g ' ol' lactate fbrmed. Asstrming t l r i s v a l u e i s c o r r e c t . la c t a t e c a n b e e x p r c s s e d i n c a l o r i e s in s t e a d o t ' g r a m s . o n a s c a l e a l s o r e p o r t e c l o r l t h e r i g h t O r d i n a t e . F r o n ] M a r g a r i a c t a l . ( 1 9 6 3 b ) . 50
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6 o z
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2.2. Tlre energeti(' .;ignit'it'un('c ol luctic ucid pr0du('ti0tl
T h e l a c t i c a c i d c o n c e n t l ' a t i o n i n t h e b o d y l l u i d s reflects the balance between lactate prodr.rction a n d r e m o v a l . T h e l a t t e r t a k e s p l a c e i n s e v e r a l o r g a n s a n d t i s s u e s . s l l c h a s t h e l i v e r . t h e k i d n e v . t h e b r a i n . t h e h e a r t . a s w e l l a s s k e l e t a l rn u s c l e . a n d c a n l e a d t o e i t h e r l a c t a t e o x i d a t i o n t o CO. a n d w a t e r ( B r o o k s e t a l . . 1 9 9 9 ) . o r t o _ulycoger-r resynthesis. During severe r'xercise. _rlycogen r e s y n t h e s i s i s s e v e r e l y d e p r e s s e d . i f n o t a l t o g e t h e r a b o l i s h e d " s o t h a t l a c t a t e r e m o v a l i s d u e e x c l u -s i v e l y . o r v e r y n e a r l y s o . t o i t s o r i c l a t i o n . t h e f i r s t s t e p o f w h i c h i s t h e r e v e r s i b l e t r a n s f b r n t a t i o n o f l a c t a t e t o p y r u v a t e . I t i s o b v i o u s t h a t l a c t a t e o x i d a t i o n . e x a c t l y a s p y r u v a t e r e m o v a l i n t o the K r e b s c y c l e . r e q u i r e s o x y g e l t c o n s u m p t i o n with the same stoichiometric coeflcient (rnoles of sr-rb-s t r a t e p e r n ' r o l e sr-rb-s o f o x y g e n ) . A s a c o n s e q L l e n c e . w h e n l a c t a t e p r o d u c t i o n e q u a l s la c t a t e removal. s o t h a t t h e l a c t a t e c o u c e l t t l a t i o n in b o d v f l L r i d s
s t a y s c c - r n s t a n t " t h e r a t e o l - o x y g e n c o l l s u l l p t i t r n is an overall r-neAsLn'e of the whole body ener-qy e x p e n d i t u r c . r e _ q a r c l l e s s o f - t h e r n a _ u n i t u d e o f l a c -tate production ancl rertror,'al and of the absolr,rte l a c t a t e c o n c e n t r a t i o n . T h i s i s w h a t o c c u r s d r - r r i n g l i g h t a e r o b i c e x e r c i s e . O n t h e c o n t r a r ) , . d u r i n g i n t e n s e c r c r c i s e . w h e n t h e l a c t a t e c o n c e n t r a t i c - r n i n t h e b o d y f ' l r " r i d s k e e p s in c r c a s i n _ u . t h e w h o l e b o d y e n e r g y t u r n o v e r i s l a r g e r t h a n t h e oxygen con-sut-uptic-l-r by an iuloLlnt that is proportional tcr t h e n e t r a t e o f l a c t a t e it c c u n t u l a t i c - r n .
T h e s e g e n e r a l c o n s i d e r a t i o n s a r e d e t a i l e c l rn F i g . 2 . i n w ' h i c h a n u n t b e r o f schernatic w o r k i n g hypotheses for lactate prodr-rctiolt ancl rentol,ill arc p r e s e n t e d a t t l i e l e v e l o f m u s c l e fi b r e s ( d i P r a n t -p e r o e t a l . . 1 9 9 8 ) : ( i ) a n " e v e n l y a r e r o b i c ' c o n d i t i o n . i n w h i c h e a c h f r b r e r . r t i l i s e s t h e p y n - r v a t e t h a t i t p r o d u c e s . s o t h a t n o c h a n g e in l a c t a t e c o n c e n t r a -t i o r - r o c c u r s a s c o n t p a r e d t o r e s t : ( i i ) a ' h y p o a e r o -b i c ' c o n d i t i o n . i n w h i c h a c t i v e f i -b r e s p r o d u c e nlore pyrr-rvate than carr-r be oxidised in the Krebs c y c l e . s o t h a r t la c t a t e c o n c e n t r a t i o n k e e p s in c r e a s -2La 6 0 : rco: 6 o r 6CO: 6 o r 6CO: g I 1 ' c o g c I r t r r l i t t r t i l i s e c l ( l 6 2 . u o 1 . g l y c c l g e r l ) 1 ' i e l c 1 s 3 r l l c l l t l | A T P i r l t h c i n i t i l r l p I r l t s c t r l ' t l l c p t l c e s s ct'clc. TI-re P O. nrticr i s h i g l r e r t I r a n i t l s t i t t l c l a r c l a e r o b i c c t l I l c 1 i t i c l r l s : t I l c K r e b s c l . c l e . T h e P o . r . a t i o i s l o u ' c r t I l a r l i t l s t a t l c 1 a r c l l t e r o b i c c t l t r c 1 i t i t l r l s : l i r r s t a n d a r d a c r o b i c c o n d i t i o r t s ( i ' 1 + 3 . 1 * 6 ) l l : 6 . 1 7 . A s i n d i c u t e c i b 1 ' t h c l r r r o \ \ . t h c l i r c t a t c c o n c e n t r a t i o n i s h i g h c s t i 1 t h c s p a c c . F r o r n d i P r a n t p e r o c t u l . ( l 9 t ) 8 ) .
p . L . t l i I ' t . t t t i l 1 t L , t . t t . ( t . I . ' t , r t ' L , t l i ! l t ' . s p i r t t t i r t r t I ) l t t " s i t t l r t t . r l t E ( 1 9 9 9 ) 1 0 1 l l 5
i n _ c s t e a c l i l . v : ( i i i ) i r . h y p e r a e r o b i c ' c o r l c l i t i o r l . i r l T h c r e s u l t s p r e s e l l t e c l i n F i g ' I a t ' e t t o t i n h e r -which t5e active fibres take r.rp ancl oxiclise lactate crrtlv cc-rtttraclictorv u'ith the cLlrl'cllt tlt'rtiot.t fr.r.r-r the ertracellr.rlar space in acrclition to or u'hereby bloocl lactate collcclltrtrtiolr is plotted
as i r - r s t e a c l o l - t h a t p r o d u c c c l b v t h e n r s e l v e s . s o t h a t a f u n c t i o n o l - t h e e r e r c i s e i n t e r l s i t - v ' I n c l e e c l '
t h e l ' l a c t a t e c . r r c e r r r a t i o ' k e e p s c l e c r e a s i n - u s t e a c l r l l ' : c l e s c r i b e c l i f t e r e n t t . c e 1 s o f t h e
' l a c t a t e ' r ' l o r l d ' T h e ( i r , ) a n . u r e r , e r l y aerobic' conciition \lùcrein thc l a t t e r i s a s t a t i c p i c t u r e . re p o r t i l l g li t c t i t t c
c o l l c e t l -l a c t a t e p r . c l u c e c l i , e x c e s s b y h y p o a e r o b i c f l b r e s is t l a t i o n a t a -uiveu p o i r l t i r l t i r l r e ' r e g a r d l e s s 0 1 ' t h e t a k e , ' p a n c l o r i c i i s e c i b , v b y h y p e r a e r o b i c f i b r e s p r e c e c l i n g c v e r t t s : t h e f b r n - r e r ( F i g ' l ) i s a c l y r l a r t r i c l 1 e a r b y . s o t h a t . a f ï e r a r i n i t i a l r i s e n c c e s s a r , v t o p i c t r - r r e l e p o r t i r l g t h e r a t e o 1 - i t i c r e a s e o f l a c t a t e p r i m c t h e s y s t e m . la c t a t e c c ) n c e n t r a t i o r - r r e m a i n s c O n c e u t | a t i o n c l u r i r l g t l - r e e r e r c i s c p e r i o c l i r l w h i c h stable at a higher. lei,,el than the restin-u. It shoulcl the o. cousut-l-tptiorl l-ras attairlecl
a collstilllt' arlcl a l s . b e p o i . t e d o u t t h a t t l - r i s s t a t e o f a f f . i r s i s i ' t h a t v c r v i r i s t . . c c r ) r a x i r ' a l '
v a l u e ' ciepcnclcr-rt o|r" ancl tacilitated by" the eristettce of
a l r r c t a t e tr a r s p o r t e r ( J r - r e l . r g g i ) . T h e t o ' r h y - 2 . 3 . T t r c d i . s t r i l t t t t i . r t ' f l u . t , t t ' p o t h e s e s c l e t a i l e d r n F i g . 2 . o n c e tr a n s l a t e d t o t h e
rvhole bocli, lcvel. rrre c.nceptu.l n'alogucs of The ar.r-r.Lr-rt of lactate
'prtlclltcccl' per kg of l i _ u l - r t a e r ' b i c e x e r c i s e . s L r p * l l ' r a x i ' r r u l c r e r c i s e . r e - b o c l 1 " t t t a s s ( M a r g a r i i t e t a l " 1 9 6 3 b ) r ' v a s c a l c l r l a t c c l coverv tbllowing supramaxirnal exer-cise. arrcl in- assufr]ir]-u that the peak bloocl lactiite cc-rttcetltfit-t e n s e a e r o b i c e x e r c i s e ( p o w e r a b o v e 5 0 ' x , o l ' t h a t t i o n a t i c r e r e r c i s e " a t t a i r l c c l
b e t w e e t l t h e - 5 t l i a r l d corrcsponclin-u to the maximal ox)--rrcn Sth n-rin ol' recoverv" \\'as il llleasLlre
o1- the eqtri-c . r r . r s . r m p t i o ' ) .
t L ' L r r L r r r * / \ r r r r L ' r - ' :
l i b r i u m l a c t a t e c o n c e l r t r a t i o n t h r o t t g h t l r - r t t h e b o d l ' ' This general picture is conceptualll,' iclcntical to w'ater. This u'as ttlso assltt-tlecl ttl be eclr'ral
irl the t h a t r _ r r - r d e r l y i n g t h e s o c a l l e c l ' l a c t a t e shuttle' c l i t l è r c n t ti s s r - r c s . r c g a r d l e s s o f t h e i r i t l t r i t - v e f s L l s ( B r o o k s . l g 1 3 5 ) . r v h i c h w i l l n o t b e c l i s c r - r s s e c l f u r - e r t r a - c e l l u l a r $ ' a t c t ' f r a c t i o n s ' T l i e l a t t e f ' h o w e v e r ' t h c r i , t h i s p a p e r . H o w e v c r . . r 1 i r - ' ' - r e c l i a t e c . r o l - i s t o t t h c c a s e . s i t r c e l l t c t a t e a t l i c - r t - t s a t e q r - r i l i b r i u r n lar.v o1- tl-re ab.re li'c of reasor-ri'g is that the are plctèrentialll'' lttcatcd ir-r the extra-cellttlar c r e r g e t i c s i g ' i f i c a r - r c e o 1 - la c t a t c c l c f e n c l s o n t h e p h a s e ( R o t - r s . 1 9 7 - 5 ) . s t l t h a t t h e a l n o l t t - t t
o f l a c t a t e rate at whicli its cr-'rcertrati.r-r chan-ues in the pet kg of boc11, mASS clttrtrot be easllir calcr-rlatecl b o c l y fl r - r i c i s . a ' c 1 ,o t t o i t s a b s o l u t e . . - , , - r . . , - r t r , r t i o n . w i t h o u t k n o u ' ' l n g t h e l a c t a t c c t r t t c e t i t r a t i o n s
i n A s a c o n s e q u e n c e . t h e w i c l e l y r, r s e c l r e p r e s e n t a t i o r - r i n t r a - r t n c l c x t r a - c e l l r - r l a r \ \ a t e r ' t o g e t h e r rv i t h t h e of the bloocl lactate concelrtration as er l-ur-rctit-rr-r of correspoliclirlg ll'actitlrls' In addititln' Margaria et t h e c x e r c i s e i n t e n s i t y c : r ' n o t a r - r c l s h o u l c l n o t b e a l . ( 1 9 6 3 b ) c l i c l n o t c c - r n s i d e l ' t h l t t r t c e t ' t i t i t t i l l l l o L l n t ir-rter.pretecl to mea' that. u,henever bloocl lactate of- lactatc is irlcr,'itabll" remol'ccl cllrrirl-s the first c . r c e r t r a t i o n e x c e e d s a g i v e n t h r e s h o l c l ( c . g . 4 1 i ' c m i n u t c s o t ' r e c o v e r ) ' . b e f t l r e th e a t t a i r l t ' u e l l t O t ' n r M ) . t h e e ' e r g y r e q u i r e r - r e r t o f t h e e x c r c i s e i s t h e p e a k b l o t t c l la c t a t e c o l l c e l l t r i ' t t i . t l ' T h e r e l o r e ' m e t i , p a r t b y a r a e r o b i c l a c t i c e l r e r g y s o L l r c e s . t h i s i s n e c e s s a r i l r l e s s t h a t l i t w O u l d b e ' w e r e I r l c l e e c l . t l r i s l v l c i e l y r r s e c l r e p r e s e t l t i r t i o r l o n l i , i n l l a c t a t e c l i f T L r s i o r r a l l c l n l i x i t l g i r i s t a r l t i l l l e O [ t S . I t f b l -p l i e s th a t . c l ' r i n g a c e r t a i r - r p e r i o c l o f t h c e x c r c i s e . l o r v s t h a t M i l r g a r i a e t a l ' ( 1 9 6 3 b ) p e r l o r n " r e d i I r-rsually in its early phase. befbre the attainr-nent ol- rather crucle estit'tlate ot' lactic acid proclr'tctic-rt-t a s t e a c l y s t a t e i n o x y g e u c o n s l ' r l p t i . n . i t c e r t a i n l l ' o m p e a k b l o o c l la c t a t c c o l l c c l l t f t l t i c l ' '
T h i s s t a t e -f'rorrt of erergy has been clerivecl from alucfo- ment- howel'er. by rlo mealls irllplies reiectiorl
of bic larctic e.ergy sources. whence the increase of the cotrcept of tlte ertergetic significallce o1' blood b l o o d l a c t a t c c o l l c e n t f a t i o l l ( e a r l y l a c t a t e " a s l a c t a t e a c c L t m u l a t i o t ' t ' d e f i r - r e c l b y c e r r e t e l l i e t a l . . l g l g . s e e b e l o r , v ) . I t I f u ' c a s s L r n l e t h a t : ( i ) t h e p e a k b l o o d l a c t a t e a l s o t b l l o w s t h a t a c o n t i n u o u s a n a e r o b i c l a c t r c c o n c e n t r a t i o n i s t h e r e s r - r l t o 1 ' a t l e q L r i l i b r i t l l l l c o l l -c o n t r i b u t i o , t o t h e e r e r g y r e -c l u i r e m e n t c a n b e c l i t i o n . w h i c h i s i r l c l e p e n d e n t o f t h e a c t t r a l la c t a t e d e r n o r i s t r a t e d o n l y i f t h e l a c t i r t e c o n c e n t r a t i o n c o n c c n t r a t i c t t - t i n e x t r a - a t l c l i n t r a - c e l l u l a r f l u i d s : k e e p s ir . r c r e a s i n g d u r i r g t h e e r e r c i s e . a n c l ( i i ) t h e r i t t c s o f l a c t a t e c l i s a p p e a l i l l l c e i r l t l i e
I 0 8 P . L . l i P r t r t r r l t t ' r o . G . F L ' r r L ' t t i l l c . s p i r t r t i o t t P l r . t ' . s i o l o g t l l E ( 1 9 9 9 ) l 0 - 1 1 1 5
varioLls body flr-rid cor-r-rpartments have tl-re stltllc t i n r e c o n s t a n t s . t h e n t h e k i n e t i c s o f l a c t a t e d i s a p -p e a r a n c c l l ' o m b l o o d s h o u l d b e a p p r o p r i a t e l y d e -s c r i b c d b y a m o t - t o e x p o n e n t i a l . T h i s i s i n d e e c l t h c c a s e ( M a r g a r i a e t a l . . 1 9 3 3 : A s t r a n d . 1 9 6 0 : M a r -g a r i a e t a l . . 1 9 6 3 b : H e r r n a n s e t t a n d S t e n s v o l c l . l L ) 7 2 : d i P r a m p e r o e t a l . . l 9 7 8 a . b ) . th e h a l l ' - t i n - r e o f t h i s m o n o e x p o n e n t i i t l b e i n g : ( i ) o f a b o u t l 5 r - n i n f b r r r r e s t i n g r e c o v e r y : ( i i ) f a s t e r i f l i g h t aerobic exercise is perfbrmed during recovery ( G i s o l f i e t a l . " 1 9 6 6 ) : a n c ' l ( i i i ) i n d e p e n d e n t o f - t h e a b s o l r . r t e p e a k b l o o d l a c t a t e c o n c e n t r a t i o r t . a t l e a s t i n t h e r a n g e b e t w e e n 4 a n d l 6 n t M ( d i P r a n t p e r c - r e t a l . . l 9 7 B a . b ) . A s a c o n s e q L r e n c e . p r o v i d e d th a t t h e c o n d i t i o n s o f ' r e c o v e r y a r e s t a n d a r d i s e d : ( i ) tlie p e a k b l o o c J l a c t a t e c o n c c t r t r a t i o r t d u r i r t g r e c o v e r y i s . a n d c a n n o t b r " r t b e . d i r e c t l y p r o p o r t i o n a l to t h e o v e r a l l a m o L l n t o f l a c t a t e a c c u m u l e t t e d i r t I k g o f b o d y r l r I S S d u r i n g t h e p r e c e d i t t g s u p r a r n a r i m a l e x e r c i s e : a n d t h u s ( i i ) t h e r a t e o f l a c t a t e a c c u m u t l t t -t i o n i n b l o o d . a s c a l c u l a -t e d f i o m t h e r a t i o o f t h e p e a k b l o o c l la c t a t e c o n c e n t r a t i o n t o t h e d r - r r a t i o r t o l - t h e p r e c e c l i n g e x e r c i s e . i s . a n d c a n n o t b u t b e . d i r e c t l y p r o p o r t i o n a l t o t h e r a t e o f l a c t a t e a c c l t -r l u l a t i o n i n 1 k g o f b o d y n t a s s . A n d t h i s i s s c - -r . e v e n if i t i s v e r y d i f Ï c u l t . i f n o t a l t o g e t h e r i m p o s -s i b l e . to c a l c u l a t e o r f f l e a s L l r e t h e l a s t . I n o t h e r t e r m s . th e r e is n o n e e d o f d e t e r m i n i n - e t l ' r e ra t e o f l a c t a t e a c c u m u l a t i o n p e r k g o f b o d y nlass to -uet infbrntation on the energy released by a n a e r o b i c l a c t i c m e t a b o l i s r - n . I t w o u l d b e e n o r . r g h t o c a l c u l a t e t h e r e c i p r o c a l o f t h e s l o p e o f t h e l i n e . t h a t r e l a t e s th e m e a s u r e d r a t e o 1 ' la c t i c a c i d i r t -c r e a s e ir - r b l o o d ( A [ L â ] . A t ' ) to the known metabolic power reqr-rired to perlbrnt the corre-s p o n d i n g e x e r c i corre-s e corre-s ( A E A t ' ) . T h i s p a r a m e t e r . w h i c h i s f i o m h e r e o n d e f i n e d B : ( A E A t ' ) ( Â [ L â ] n A t ' ) I : A E A [ L â ] b '. i s i n d e e d t h e c o -e l Ï c i -e n t y i -e l d i n g th -e a m o u n t o f -e n -e r g y p -e r u n i t o f b o d y m a s s re l e a s e d b y t h e a c c u m u l a t i o n o f I m M o f l a c t a t e in b l o o d . F r o m t l - r e d a t a o f M a r - e a r i a e t a l . ( 1 9 6 3 b ) . B t u r n s o u t t o b e 3 . - 3 rt t l O . k g I m M r . w h i c h n r e i l n s t h a t a r - r y I m M i n c r e a s e i n b l o o d l a c t a t e c o n c e n t r a t i o r " r i s e q u i v a l e r - r t t o t h e e n e r g y re l e a s e d b y t h e c o n s L u r p t i o n o f 3 . 3 m l O . p e r k g o f b o d y m a s s . T h i s i s a n e m p i r i c a l e n e r g y e q u i v a l e n t . c l e t e r m i n e d w i t h o u t t h e n e e d o f a n y a s s u m o t i o n a s t o t h e e f f e c t i v e d i s t r i b u t i o n o f l a c -t a -t e . I -t c a n b e s a f è l y a p p l i e d a s s u c h . p r o v i d e d th e e x p e r i m e n t a l c o n d i t i o n s a r e t h o s e d e s c r i b e d a n d discr-rsseci above.
2.4. The arrcrgatit',s of .utprurtu.ritrtul e.rert'i.va Dr-rring sLlpramatximal exercise" the oxygen con-s u m p t i o n m a y a t t a i n i t con-s m a t x i n - r a l v a l u e w i t h i n s a y 2 0 3 0 s e c . A f ï e r t h i s i n r t i a l t i m e . w e c a l t r e a s o n -a b l y -a s s r - r m e t h a t l ' l o e l t e l ' g e t i c c o n t r i b u t i o n f r o m a n a e r o b i c a l a c t i c e n e r g y s o u r c e s ( L o h r n a n n r e a c -t i o n ) s u b s i s -t s . S o t h e e n e r g y r e l e a s e p e r u n i t o f t i m e a f ï e r t h e i n t t i a l p e r i o d i s t h e s L l m o f t w o terms. the first refèrring to aerobic" the second to a n a e r o b i c l a c t i c . e l t e r g y p r o d u c t i o n s . A S fo l l o w s : c l E d t : ( d v o r ' d t ) , , , , , . + / ( d [ L â ] , , d t ) ( l ) whcre dE,,'dt is the overall r-r"retabolic power. ( d V O . d t ) , , , , , , i s t h e m a x i m a l a e r o b i c p o w e r . B is t h e e n e r g y e q L r i v a l e r - r t o f l a c t a t e a c c u m u l a t i o n i n b l o o d . a n c l (d [ L â ] , , , d t ) t h e r a t e o f l a c t a t e a c c u m u -l a t i o n i n b -l o o d . I f d E , d t i s i n m -l O . t t t i t - t ' kg I a n d ( c l [ L â ] , . d t ) i n t n M n r i r t r . t h e n B i s i n m l 0 2 m i t ' r I m M ' ( 3 . 3 a c c o r d i n g to M a r g a r i a e t a l . . 1 9 6 3 b ) . lf r v e e x p r e s s d E , d t r e l a t i v e t o ( d V O . , ' d t ) , , , , , r . E q . ( 1 ) b e c o m e s : c l E d t , / ( d [ L i l r , d t )
( . l v q . .itt*
: I _-
t . r v o , . . r t l " , , ^
( 2 )
E q . t2) allows a comparison of subjects d i f f e r i n g in rnaximal aerobic power. and therefbre working a t d i f l è r e n t s L r p r a m a x i m a l e x e r c i s e i n t e n s i t i e s w i t h d i f f e r e n t e x e r c i s e m o d e s . F r o m t h e d a t a o f M a r -g a r i a e t a l . ( 1 9 7 1 ) d u r i n g t r e a d n - r i l l r u n n i n g a n d o f P e r - r d e r g a s t e t a l . ( 1 9 7 1 ) d u r i r t g s w i n i n t i r i g . i t w a s p o s s i b l e t o c a l c u l a t e [3 fiom Eq. (2) for the two e x e r c i s e m o d e s a t s t a k e . T h e r e s u l t s a r e s h o w n i n F i g . 3 . w h e r e d E ' d t i s p l o t t e d a s a f u n c t i o n o f d [ L â ] b ' d t . b o t h e x p r e s s e d r e l a t i v e to t h e m a x i m a l o x y g e n c o t - t s u m p t i o n . f b r r u n n i n g a n d s w i m m i n g . T h e t w o r e g r e s s i o n l i n e s h a v e s i m i l a r s l o p e s . i n d i -c a t i n g t h a t t h e e n e r g y e q u i v a l e n t o f b l o o d l a c t a t e a c c u m u l a t i o n fo r t h e t w o e x e r c i s e m o d e s i s t h e s A n r e ( 3 . 0 ln d 1 . 7 m l O , k g I m M r . f o r r u n n i n g and swimn-ring respectively. to be con'rpared to the f i - e u r e o f 3 . 3 m l O , k g I m M r d i s c u s s e d a b o v e ) . M o r e r e c e n t l y . C a p e l l i a n d d i P r a m p e r o ( 1 9 9 5 ) m e a s u r e d d [ L â ] b ' d t d u r i n g s u p r a m a x i m a l tr a c k
P . E . d i I ' r r t t r r p t ' r p . G . I ' c r r t ' t t i R c . s p i t ' t t t i t t r t P h . r " t i o l o , u , . t ' l l 8 ( 1 9 9 9 ) 1 0 1 l l 5 I 0 9 c y c l i n g . i n a c o n d i t i o n i n w h i c h t h e o v e r a l l n - r e t a b o l i c p o w e r w a s k n o w r l . T h i s a l l o w e d a p p l i -c a t i o n o f E q . ( 2 ) l o r t h e -c o m p u t a t i o n o l P. wlii-ch r e s u l t e d e q L l a l t o t h a t c a l c u l a t e d f o r r u n n i n g a n d swin'rming. T h e s t r i k i n g s i m i l a r i t y o f t h e s e v a l u e s . i n d e p e n -clent of subjects. type of exercise. ir-rtensity of e x e r c i s e . a n d m u s c l e s i n v o l v e d . r e i n l o r c e s t h e v i e w t h a t B is indeed the energy equivalent of blood l a c t a t e a c c u m u l a t i o n . a n d s u p p o r t s i t s -qeneral v a l i d i t y . C l e a r l y e n o u g h . B is not the ener-uetic e q u i v a l e n t o f l a c t a t e f b r m a t i o n i n t h e w o r k i n g m u s c l e s a n d d o e s n o t y i e l d a n y d i r e c t in f b r m a t i o n o n t h e s t o i c h i o m e t r i c r e l a t i o n b e t w e e n l a c t a t e f b r -r"r-ratior-r and ATP resvnthesis. It is nevertheless a
F ig . 3 . T h e o v e r a l l r a t e o f e r r e r g y c x p e n d i t L t r e ( d E d t ) i s p l o t t e d a s a f - u r - r c t i c t n o f t h c r a t e o f l a c t i c a c i c l a c c u r n u l a t i o r l i n b l o o d ( d [ L â ] ' , d t ) i n r t t n n i n g ( f r - r l l c l o t s . d a t a l l ' o t r - r M a r g a r i i t c t a l . . l 9 7 l ) a n d s w i n t m r i n g ( o p e n d o t s . d a t a f r t l n r d i P r i t n l p e r o e t a l . . 1 9 7 8 b ) . T h e c o m p a r i s o t t o f d i l l e r e n t s u b j e c t s is m a c l e p o s s i b l e b y ' e x p r e s s i n g b o t h p a r a m e t e r s a s r a t i o s t o t h e s u b -j e c t s ' maximal oxy"gen c o n s u m p t i o n . T h c r e g r c s s i o n l i t l c s a r e : r ' : l . 0 l + 2 . 9 6 . v ( r ' : 0 . 9 9 ) . a t r d . t ' : 0 . E 5 + l . 7 l r ( r ' : 0 . 9 ' 1 ) . l b r r u n r r i n - e a n d s u ' i m m i n g . r e s p c c t i v e l y . T h e s l o p c c l f t h e s c li t t e s c o r r e s p o n d s t o t h e e n e r g y e q t r i v a l c n t o l ' b l o o d l a c t a t e a c c l l l l l t l -l a t i o n . M o d i f i c d a f i e r c -l i P r a m p e r o ( 1 9 8 1 ) . v e r v u s e f u l q u a n t i t y a l l o w i n - q L l s to d e t e r m i n e t h e energy release it't thc body whenever the blood l a c t a t e c o n c e n t r a t i o n i n c r e a s e s b y a g i v c l l a l l l o L l l l t . 2.5. Tha trrtr.uittrul lur'îit' power
S i n c e d [ L â ] , , d t i n c r e a s e s l i n e a r l y w i t h i n c r e a s -ing the exercise inter-rsity. it n-ray be expected that it attains a lttttxitttLllr wheu tl-re ellergy release fl-on'r aniterobic lactic metabolisrll t'etlLtires ex-p l o i t a r t i o n o f t h e -ulycolytic p o t e n t i a l a t i t s g r e a t e s t e x t e l r t . T h a t t h i s i s i n c l e e d t h e c i t s e w a s d e m o n -strated. agair-r in the sixties. by r-r-ren-rbers of the S c h o o l o f M a r g a r i a ( i n c l r - r d i n g P a o l o C e r r e t e l l i ) i n a n e l e g a n t s e r i e s o f e x p e r i m e n t s i n w h i c h s u b j c c t s r u n o n a t r e a d m i l l lt 1 8 k n r h I at slopes up to
25"/,,. thus perlormirtg exercises reqr-riring il n - r e t a b o l i c p o w e r l a r g e r t h a n t w i c e t h e m a r i m a l a e r o b i c p o w e r ( M a r g a r i a e t a l . . 1 9 6 4 ) . T l i e r e s u l t s s h o w e d t h a t : ( i ) d I L â ] b d t e t t t a i n s a c o t r s t i t t t t t t i a x i -m a l v e r l u e w h i c h d o e s n o t i n c r e a s e b y f u r t h e r i n c r e a s i n - u t h e e x e r c i s e i n t e r t s i t y : a n d ( i i ) t h e t i m e a f t e r w h i c h d I L â ] ' , d t s t a r t s i n c r e a s i n g i s s h o r t e r t h e h i g h e r th e e x e r c i s c i n t e n s i t y ( F i g . 4 ) . M a r g a r i a e t a l . ( 1 9 6 4 ) a r g u e d th a t t h e e n e r g y s o L l r c e s f b r t h e t i m e t h a t p r e c e d e s t h e i t t c r e a s e i n d [ L â ] ' , ' d t w e r e a n a e r o b i c a l a c t i c . n a m e l y t h e r - r e t u t i l i s a t i o n o h l-righ energy phosphates. particr-rlarly phosphocre-a t i n e . b e c phosphocre-a u s e o f t h e c o n t r a c t i o l l o f t h e a l a c t i c oxygen deficit and because tlle intensity of exer-c i s e w a s m u exer-c h l a r g e r t h a t r t h e m a x i m a l a e r o b i exer-c p o w e r .
K n o w l e d - u e o f B. calculated a s d e s c r i b e d a b o v e . a l l o w e d a u e s t i m t t t e o f t h e r r e t a b o l i c p o w e r e q u i v -alent of the measllred rnetximal rette of lactate a c c u n - t u l a t i o n i n b l o o d . o r m a x i r n a l la c t i c p o w e r : t h i s a m o u n t e d t o s o m e 7 5 m l O , k g I min r. i.e. a b o u t 1 . 5 t i n t e s t h e s u b j e c t s ' m a x i m a l a e r o b i c p o w e r . I t w t t s h i g h e r i n p o w e r a t h l e t e s ( H e r -m a n s e n . l9 1 l \ . a n d r e d u c e d a f t e r a l t i t u d e a c c l i m a -t i z a -t i o n (G r a s s i e t a l . . 1 9 9 5 ) .
2.6. Tlte rrtuxiltul luçtit' r'ttttttt'itt'
The above data can also be r-rsed to draw all o v e r a l l e n e r g y b a l a n c e o f v e r y s t r e n u o t t s e x e r c i s e i n h u m a n s . F r o m t h e ( k n o w n ) t o t a l e n e r g y r e -q u i r e m e n t o f t h e e x e r c i s e . t h e ( m e a s u r e d ) a m o u n t y = 1 . 0 1 . r 2 . 9 6 x * Y = O . 8 5 + 2 - 7 2 x
I l 0 P . E . d i P r u r r t l t c r t t . G . F t , r r a t t i l l c , s p i r r r t i o r t P h . t . s i o l o s . t l l S ( 1 9 9 9 ) 1 0 - 1 1 1 5
sêc
r . n l ) a s a l - u t r c t i o n o l ' c r c r c i s c c l u r a t i o n (s e c ) . T h c l b u r l i n c s r e l è r t o l i t u r u o r k t h c t r c ' a d m i l l l ' r o m l 0 t o l 5 ' l , , " a t t h e c o n s t i t r l t s p c e d o f l 8 k n t h r . T h e s l o p e i n b l o o c l . S i n c c it i s u n c l t a n g e c l b r i n c r e a s i n g t h e p o \ \ e r o L l t p L l t ( s e e re g r e s s i o n r a t c c t f ' e n c r g ) r c l c i t s c b 1 ' b l o o c l la c t a t e u c c r . r m u l a l i r ' r r . r . c l r n ' t l r t i r . n a l l a c t i c p o \ \ ' c r .: 4 0
Q\ s ç: 3 0
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2 0
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F i g . ' 1 . ln c l e u s e o l ' l a c t i c a c i d i n b l o o d ( i n r n g p e l l { ) t ) l o i t c l s " u n c l ll ' e l e o b t a i n c d b 1 ' c h a n g i n g th c i n c l i n e o n i n d i c a t c s t h c r a t c a t r , r . h i c h l a c t i c a c i d i s a c c u n t u l a t c c l c c l u u t i o n s o n t h c f i _ c . ) . i 1 c o r r c s p o n d s t o l h c r . n u r i n t a l F r o m M a l g a r i a e t a l . ( 1 9 6 . 1 ) . o f l a c t a t e a c c l l m u k l t e c J i n b l o o d a f i e r e x h a L l s t i o n -t h e ( c a l c u l a -t e d ) v a l L r e o f 0. the (n-reasured) s u b -j e c t s ' maximal aerobic power. and from the k n o w l e d g e o f t h e t i m e c o n s t a n t o f t h e O , c o n -s L l m p t i o n k i n e t i c s th a t s e t s th e a l a c t i c O r d e f r c i t ( 2 3 . 3 sec. Binzoni et al.. 1992). it is possible to c a l c u l a t e t h e a m o u n t o f e l t e r g y t h a t c i u t be d e r i v e d fl ' o n - r t h e f u l l u t i l i s a t i o n o f a n a e r o b i c l a c t i c e n e r - q y s t o r e s . o r m a x i m a l l a c t i c c a p a c i t y . T h i s r a n g e s . fo r c o n t i n u o l l s e x e r c i s e , b e t w e e n 4 5 a n c l 5 5 m l k g c o r r e s p o n d i n g t o a b l o o d l a c t a t e a c c L l m u l a t i o n o f a b o L r t l4 l 7 m M . I t v a r i e s w i t h t h e a c t i v e m l r s c l e n r a s s . i s h i _ e h e r i n p o w e r a t h l e t e s t h a n i n n o n - a t h l e t i c s u b j e c t s . c a l l b e t w i c e as b i g a f t c r i n t e r m i t t e n t e x e r c i s e ( O s n e s and Her-m a n s e n . l 9 l 2 ) . a n d i s d e c r e a s e d a f i e r a l t i t u c l e a c c l i m a t i z a t i o n ( s e e " e.g. Cerretelli and Binzoni.1 9 9 0 ) . L a c t a t e a c c u m u l a t i o n in m u s c l e i s o b v i o u s l y a s s o c i a t e d w i t h a s i m u l t a n e o u s i n c r e a s e in H t c o n c e n t r a t i o n . T h u s . t l - r e l i n - r i t s t o m a x i m a l l a c t i c c a p a c i t y a r e l i k e l y i r - r - r p o s e d b y t h e m a x i m a l H ' c o n c e n t r a t i o n t h a t c a n b e a t t a i n e d in t h e w o r k i n g m u s c l e s " b e f b r e i n h i b i t i o n o f g l y c o l y s i s . T h i s i n turr-r depends on the bull'er characteristics of mus-c l e f l b r e s a n d b l o o d " a n d o n t h e r a t e a t w h i mus-c h lactate can be removed l'rom r-nuscles. This. how-e v how-e r . m a y r - r o t b e t h e c i t s e i n a l t i t u d e a c c l i m a t i z e d sr-rbjects. in whom an increase in buf-fer power t h r o u - e h b i c a r b o n a t e a c l n r i n i s t r a t i o n f à i l e d t o i n -c r e i l s e t h e m a x i m a l l a c t i c c a p a c i t y (K a y s e r e t a l . . 1994). : . 7 . T l r c P L u r t r t i t t T h e e n e r g y e q r - r i v a l e n t o f l a c t a t e a c c u m u l a t i o r t i n b l o o d i s a n e p i p h e n o r n e n o n i n d i c a t i n g t h e amount of ener-{y released by anaerobic energy s o l r r c e s f b r r e s y n t h e s i z i n g A T P . t h e h y d r o l y s i s o f w h i c h a c t u a l l y p r o v i d e s t h e e n e r g y f o r contrac-t i o n . T h e k n o w l e d g e o f t h e a m o u n t o f A T P r e s y n -thesised fionl the accumr.rlation of I mol of lactate i n t h e w o r k i n g m u s c l e s . o r P , ' L a ra t i o . i s t h e r e f o r e o f p r i m a r - y i m p o r t A n c e .
p . E . tti Prtrtrrltt,r0^ ( i . Farratri IIL'.tpirtrlittn [ ' h 1 ' s i t t l t t g . t ' I t 8 ( 1 9 9 9 ) 1 0 3 1 l5 i l l In tl-ris t o l l o w s : d A T P r d t c o n t e x t . E c l - ( l ) c a n b e r e w r i t t e n a s : a(clVO:'clt),,,,,, + c f ( d I L â ] b , ' d t ) ( 3 ) w h e r e c l A T P r d t is t h e r a t e o f A T P r e s y n t h e s i s . a i s t h e P l ' o . r a t i o ( m o l e s o f p h o s p h a t e r e s y n t h e s i s e d a t t h e e x p e n s e o f t h e c o n s L l m p t i o n o f 1 m o l o f O . ) . a n d c i s a c o n s t a n t r e l a t i n g b l o o d l a c t a t e cùcentration to the anlount of lactate prodr-rced ( [ L â ] , , , ) . M e r - e i n g c o n s t a n t s i n E ' q ' ( 3 ) y i e l d s : C I A T P ' d t : a ( d V O : d t ) n . . r + b ( d [ L à ] , " d t ) ( 4 ) w h e r e b ( : c B ) i s t h e P ' L a r a t i o ' C o n r p r - r t a t i o n o f the P,La ratio fr'om the measllrement of blood l a c t a t e a c c u m u l a t i o n i n h u m a n s is i m p o s s i b l e b e -c i l u s e w e c l o n o t k n o w t h e v a l u e ta k e n b y c o n s t a u t c . I t c a n b e c a l c u l a t e d . h o w e v e r " fi o m t h e d a t a determirtecl ln isolatecl dog gastrocnemilts muscle stimLrlatecl supramaxinlally with blood flow oc-c l u d e d (d i P r a m p e r o e t a l . . l 9 7 8 a . b ) '
U n d e r t h e s e c o n d i t i o n s . t h e r e l e a s e d e n e r g y c l e r i v e e s s e n t i a l l y f i o m ( i ) d e p l e t i o u o f h i g h e n e r g y
F i g . 5 . E n t h a l p y c h a n g e (H . k . l k g r . letl orclinate' dots) and u ' c i r k o u t p u t ( \ \ ' . k J k g r . right orditrate' trirtngles) as a f u u c t i o n o f l a c t i c a c i c i lb r m e c l (L A . m m o l k g r l c l u r i n - l sllpra-r n a x i n t a l s t i m u l a t i O n o f i s o l a t e p e r f i r s e c l d o g g . t s t f o c t t e t r l i r ' t s i t l a n o x i a . T h e s l o p e s in c l i c a t c th e c n c r g l ' r e l c a s c d b y ' a r l d t h c
work pcrlbrmecl by a unit of lactic acicl lornlecl clttt'it.lg
ct'lt.t-t r a c ct'lt.t-t i o n . F r o r n c l i P r a ct'lt.t-t - n p e r o e t a l ' ( 1 9 7 8 a ) '
p h o s p h a t e s . ( i i ) l a c t i c a c i d a c c t r r n u l a t i o n ' p l r - r s a minor. negligible tturount fronl t-t'luscle O' storcs' S i n c e th e h i - e h e n e r g y p h o s p h a t e c o u c e n t r a t i o n i s constant ilt rest. ancl it clecreases down to ttlnlost
z e r o a f i e r e x h a u s t i v e s L l p l ' a n l i t x i m a l s t i m u l a t i o n ( C e r r e t e l l i e t a l . " 1 9 6 9 ) . th e e n e r g y s u p p l i e d b y p h o s p h a t e c l e p l e t i o r r i r l t h e t r a r r s i t i o r r f r o m l e s t t o stimr-rlatioll ctlll be consiclered constant' This im-p l i e s t h a t t h e t o t a l s t a r - r d a r d e r r t l i a l p y (H ' w o r k p l . . . s l - ' e a t ) c h a n g e u n c i e r t h o s e c o r r d i t i o r r s i s e q u a l t o :
H : H , , r + A H r , , [ L â ] , , ,
w h e r e H , , r i s t h e e n t h a l p y c h a n g e c l u e t o h i g h e n e r g y p h o s p h a t e s . A H , - , , is t h e n r o l a r e n t h a l p y c h a n g e d u e t o l a c t i c a c i c l f b r r l r a t i o t r t l . o r r r g l y c o -g e n . , t r t d [Lâ],,, is the overall amouut of l a c t a t e proclucecl. The relatic-lt-t betu,'eelr H and [Lâ],,, was e s t a b l i s h e d b y c l i P r a n l p e r o e t a l ' ( 1 9 7 8 a ) ' a n d i s r e p o r t e c l i n F i g . 5 . I t s s l o p e . c q r - r a l t o A H , , ' i s 7 6 k J m o l r . ancl its,t'-irltercept. e q r - r a l t o H , ' ' i s l ' 2 k J k g F u r t h e r n l o r e . a l s o t h e r e l a t i o n s h i p o f n t c c h a n i c a l w o r k o u t p n t t o l a c t i c a c i d f o r m a t i o n w a s f b u r - r c l t o b e l i t r e a r (F i g . 5 . r i g h t o r d i n a t e ) ' it s slope being iI llleetsllre of the work tlotre pet' tttole o f l a c t a t e a c c u t ' t l t t l r t t e c l ( 2 0 k J r n o l r 1 ' T h e P ' L a ratic-r citlt llow be calcr-rlrtted as the ratio of tliis last valr-re to the rvork clone per tnole of pl-rosphate split. Since the latter rallges tl'or-r-r l6 to l9 kJ r r r o l I l P i i p e r e t a l . . 1 9 6 9 : C e r r e t e l l i e t a l " 1 9 1 2 F e r r e t t i e t a l . . 1 9 8 7 : C e r r e t e l l i a n d d i P r a m p e r o . 1 9 8 8 ) . t h e P r L a r a t i o i n v i v o t L l r n s o u t e q u a l t o 1 . 2 5 | . 0 5 r r r o l o f p h o s p h a t e p e r r n o l e o f l e t c t a t e t b r r r - r e d . w h i c h i s l e s s t h a n . b u t n o t f à r f i o m . t h e value ol' 1.5 preclicted fiom stoichiorr"retry. If this i s s o . t h e e n t l - r a l p y c h a n g e o f p h o s p h a t e h y d r o l y s i s w o u l c l r a n g e b e t w e e n 6 0 a n c l 7 2 k J m o l r ' which is remarkably higher than the valtte of 46 k'l m o l ' measurecl t b r A T P s p l i t t i n g . o r o f 5 0 t h a t can be calcr-rlatecl assuming a PiLa ratio equal to t h a t i n v i t r o .3. Energetics of the oxYgen deficit
At the onset ar-r<J ofhet of square wave aerobic exercise. the O. r-rptake attains a steady level only a f t e r 3 - 4 m i n . I t f b l l o w s t h a t t h e a m o u n t o f O '
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w (.) U.t{'
l t l
that enters the body per unit of tin-re befbre the a t t a i n m e n t o f t h e s t e a d y s t a t e is less than at the s t e a d y s t a t e . S i n c e th e A T P requirement is con-s t a n t f i o m t h e v e r y b e g i n n i n g o f t h e e x e r c i s e . t h e r a t e o f O . u p t a k e during the initial phase is less t h a r - r s t o i c h i o m e t r i c a l l y r e c l u i r e d f b r f u l l y a e r o b i c A T P r e s y n t h e s i s . I t n e c e s s a r i l y f o l l o w s th a t a f l a c -t i o n o f -t h e e n e r g y re q L r i r e d f o r A T P r e s y r - r t h e s i s i s derived from other sources than O. uptake lion-r t h e l u n - q s . T h e o p p o s i t e o c c L l r s d u r i n _ e r e c o v e r y . T h e i r - r c r e a s e i n O , u p t a k e c l r - r r i n g l i g h t a e r o b i c e x e r c i s e i s . o n f i r s t a p p r o x i n t a t i o n . d e s c r i b e d b y : ( d V O . , , d t ) , - ( d V O . , d t ) , : ( d V O , r d t ; * e t r ( 6 ) w h e r e s u b s c r i p t s ' s ' a n d r r e a l t a t t h e s t e a d y s t a t e a n d a t a g i v e n ti m e t . r ' e s p e c t i v e l y . a n d w h e r e t h e t i m e c o n s t a n t t i s a b o u t 4 0 s e c . R e a r r a n g i n s e q u a t i o n ( 6 ) : ( d v o . ' d t ) , : ( d v o , c l t ) . (l - c , . ) ( 7 ) I n t h e r e c o v e r y a t t h e end of exercise Eq. (l) b e c o m e s :
( d v o . , d t ) , : ( d v o r d t l . e r r ( B ) I t f b l l o w s t h a t t h e n " r i s s i n - e o x y g e n . d e f i n e d a s O,def'. or the extra oxy-qe n during recovery ( O . d e b t 1 . i s t h e t i r n e in t e g r a l o f E q s . ( 6 ) a n d ( 8 ) : O . d e f
3.1. Tlrc cn(rg.t' ,\our('c,\ /or tlta o.\-l.g(,// tlaficit T h e e n e r - q y s o u r c e s i m p l i c a t e d in t h e construc-t i o n o 1 - t l i e O , d e f a r e e s s e n t i a l l y t h r e e : a r e d u c t i o r - r i n t h e v o l u m e o f O , s t o r e s (V O , s t ) . h i g h e n e r g y p h o s p h a t e s ( p h o s p h o c r e a t i r - r e ) breakdown ( P C r O , ) and early lactate fbrmation (eLaO.). The O , d e f i s t h e s u r n o f t h e s e t h r e e te r m s . e x p r e s s e d i n O . e q u i v a l e n t s . S i n c e la c t a t e re m o v a l f l - o n i blood d u r i n g r e c o v e r y is a r e l a t i l ' e l y slow process (see a b o v e ) . o n l y V O . s t a n c J P C r O . p a r t i c i p a t e i n t h e O , d e b t . i. e . w h a t M a r g a r i a e t a l . ( 1 9 3 3 ) c a l l e d t h e f à s t o r a l a c t i c c o m p o n e n t of the oxygen debt p a y m e n t .
T h i s s t a t e o f t h i n g s im p l i e s that. if we let one of t h e c o m p o n e n t s o f O.def vary. the two others r e m a i n i n g c o n s t a n t . the O.def should change
ac-P l r r s i o l o g r 1 1 8 (1 9 9 9 ) 1 0 3 I l 5
c o r d i n g l y a n d p r e d i c t a b l y . P a o l o C e r r e t e l l i w a s i n t h e -uroup w h i c h f i r s t l y o p e r a t e d a l o n g t h i s l i n e : in t h e g a s t r o c n e m i u s p l a n t a r i s dog preparation. l a c -tate fbnnation at tl-re onset of exercise is negligi-b l e . w h i c h s h o r " r l d l e a d t o a f à s t e r O. uptake k i n e t i c s a r " r d s r n a l l e r O , d e f t h a n i n h u m a n s : P i i p e r e t a l . ( 1 9 6 8 ) l o u n d t h a t t h i s w a s i n d e e d th e c a s e . T h u s . i n t h a t c o r - r d i t i o n , t h e e n e r g y e q u i v a l e n t t o t h e O , d e f w a s e n t i r c l y derived. or very neal-ly s o , f r o m p h o s p h o c r e a t i n e b r e a k d o w n . w h e n c e t h e n o t i o n t l i a t t h e O , d e b t w a s m a i n l y d u e t o p h o s p h o -c r e a t i n e r e s y n t h e s i s . I n a d d i t i o n . d i P r a n - r p e r o a n d M a r g a r i a ( 1 9 6 8 ) s h o w e d th a t r h e P O . r a t i o , a s c a l c u l a t e d f l ' o r l t h e r a t i o o f t h e amount ol' phos-p h a t e b r o k e n d o w n or resynthesised a t t h e o l t s e t , o l f s e t o f ' e x e r c i s e t o t h e O . d e f - . O . d e b t . i s c l o s e to t h e c a n o n i c a l v a l u e o f 6 . 1 7 .
T h a t p a p e r p r o n t p t e d a series o f e x p e r i m e n t s i n h u m a n s . i n w h i c h V O , s t was ntanipLrlated, a n d O.def for-rnd to change as predicted. A few exam-p l e s a r e d i s c r , r s s e d h e r e i r - r . V O . s t d u r i n g s t e a d y s t a t e e x e r c i s e i s s n t a l l e r th e h i g h e r the exercise i n t e n s i t y . e s s e n t i a l l y b e c a u s e o f t h e d e c r e a s e i n m i x e d v e n o u s b l o o d oxygelt saturation. s o t h a t i t s c o n t r i b u t i o n t o O , d e f oLrght to become pre-d i c t a b l y s m a l l e r in t r a n s i t i o n fionr light to heavier w o r k t h a n i n t r a n s i t i o n from rest to either work l e v e l : i t n d i n d e e d the O. r-rptake k i n e t i c s w i t s f b u n d t o b e f à s t e r in the fbrmer case (di Prampero e t a l . . l 9 l 0 ) . A n a l o g o u s l y . in acute normobaric h y p o x i a . i n w h i c h V O , s t is decreased. t h e O . d e f was fbr-u-rd to be accordingly sn-raller'(di Prampero e t a l . . 1 9 8 3 ) .
A s l i r r a s e L a O . i s concerned. C e r r e t e l l i e t a l . ( 1 9 7 9 ) lbund that r was directly proporrional to t h e l a c t a t e a c c u l l L r l a t e d i n b l o o d d u r i n g the exer-c i s e tr a r n s i e n t ( e a r l y lactate). a s f b l l o w s :
r : i [ L a ] , , * b ( 1 0 ;
w h e r e ILzr]n i s t h e e a r l y la c t a t e a n d I i s a c o n s t a n t i n c l i c a t i n g h o w m u c h r i n c r e i t s e s p e r u n i t i u c r . e a s e o f l a c t a t e in b l o o d during the exercise t r a r " r s i e n t . T h e c o n s t a n t À i s an inverse llnction of (dVO,r d t ) s . a n d f r o m t l i e data of Cerretelli et al. (1979) t u r n s o u t e q u a l t o 7 . 8 a n d 1 2 . 1 s e c m M I . a t ( d V O , d t ) , v a l u e s o f 1 . 5 a n d 1 . 0 L r n i n ' ( m e -c h a r i i -c a l p o w e r s o f 1 2 5 and 75 W), respe-crively. T h e s e v a l u e s a l l o w c o l n p u t a t i o n of the O,def
in-r
:
l t . t V o . c l t ) ,
e ' ' ) , J t : ( d v o , d t ) , t
( 9 )
l l l
P.E. di Prurttltt'r'tt. G. l't'rratti llcs:pirulittrt
c r e a s e ( i n m l O . k g ' ) p e r L l n i t in c r e t l s e i n [Lit]6 ( i n n - r M ) . w h i c h i s n o t h i n g b u t t h e e n e r g y L t l L r i \ t l -l e r r t o f b -l o o d -l a c t a t e a c c u m u l a t i o n . T h i s l a s t t u r u s o u t e q u a l to 2 . 1 9 a n d 2 . 8 9 m l k g I mM I tor the 1 2 5 a n d l 5 W p o w e r . r e s p e c t i v e l y . t w o v a l u e s a s t o r - r i s h i n g l y c l o s e to t h o s e r e p o r t e d a b o v e ( 2 . 7 3 . 3 n i l k g I n r M ' ) . T h i s s e t o f d i t t a s t r o n g l y s u p p o r t th e h y p o t h e s i s that the oxy-qen deficit results from the sir-nulta-n e o u s c o sir-nulta-n t r i b u t i o sir-nulta-n o f t h r e e e sir-nulta-n e l ' g y s o u r c e s : o x y -gen stores. phosphocreatine breakdowt't. ilnd early l a c t a t e a c c u m u l a t i o n .
3.2. Thc nat ulut'ïi(' o.\t'gctl tle.ficit
I n c o n c l i t i o n s i n w h i c h t l o e a r l y la c t a t e a c c L t m L l -l a t i o n t a k e s p -l a c e . a n d n o c h a n g e s i u O . s t o r e s ( ) c c L t r . t I c e n e r g y ;e l e i r s e d l i l l t h e c o l ' l t l ' a c t i ( ' r t t p l ' the oxygelt deficit con"Ies exclusively fl'or-r-r hi-qh e n e r g y p h o s p h a t e h y d r o l y s i s . I f t h i s i s s o - th e t i n - r e c o n s t a n t t o f t h e k i n e t i c s o 1 ' O . u p t a k e a t e r c r c i s e o n s e t b e c o m e s e q r - r a l t o t h a t o f p h o s p h o c r e a t i r l e b r e a k c l o w n . A S t h e r a t e s o f A T P s p l i t t i n g a t l c l A T P r e s y n t h e s i s z t r e e q u a l a n d t h e A T P r e s y n t h e -s i -s fi o n - r p h o s p h o c r e a t i n e s t a r t s im m e d i a t e l y a t t h e exercise onset. Indeed the tinle constant of pl'ros-p h o c r e a t i n e b r e a k d o w n d i c t a t e s t h e f ) r s t e s t p o s s i -b l e O , u p t a k e k i n e t i c s . T h i s t i m e c c - r t l s t a t l t w i t s m e a s u r e d in h u m a n s b 1 ' n u c l e a l ' n l a g l l e t i c l' e s o -nance spectroscopy and lbund to be 23.4 sec. i n d e p e n d e n t o f t h e w o r k l o a c l ( B i n z o n i e t a l . " l g 9 2 ) . T h i s v a l u e is p r a c t i c a l l y e q u a l t o t h a t l b r t . as cletert-t-tined or"r isolated perfused aerobic dog g a s t r o c n e m i u s ( P i i p e r e t a l . . 1 9 6 8 ) . A d i r e c t c o n s e -qLlence of this state of affairs is that tl-re change itl muscle phospl"rocreatine concentrattiotl durill-q the t r a n s i t i o n is d i r e c t l y p r o p o r t i o n a l t o t h e o x y g e r - t c l e f i c i t . T h i s i m p l i e s a n e g a t i v e l i r l e a r r e l a t i o n s h i p b e t w e e n p h o s p h o c r e a t i l ' l e c o l l c e l l t r a t i o l l i t t t d s t e a d y s t a t e O . u p t a k e . a s a c t u a l l y f o u r r d ( d i P r a m p e r o a n d M a r g a r i a . l9 6 8 ; P i i p e r e t a l . . 1 9 6 8 : Birrzoni et al.. 1992). T h e c o n t r a c t i o n o f a n e t a l a c t i c o x y g e n d e l i c i t is u n a v o i d a b l e a t e x e r c i s e o t l s e t . T h i s i s b e c a u s e t h e key enzymes of glycolysis need to be actir"ated for primir-rg the aerobic n-retabolisr-r-r. itnd tl-reir activat i o n i s l i k e l y m e d i a activat e d b y activat h e v e r y i n i activat i a l b r e a k -clown of liigh energy phosphates. Tl-re rlccessity of
contracting the rtet alactic oxy-qell cleficit supports the concept gctterateci ir-r the school of Margaria t h a t t h e s l o w in c r e a s e o f O . u p t a t k e a t t h e o n s e t o f s q L r a r c w a v e c x e r c i s e h a s i l n l c t a b o l i c o r i g i n " r v h e r e a s i t c o r l s t i t L l t e s i . t s t l ' o 1 1 g c v i c l e n c e a g a i r - r s t t l - r e a l t e r n a t i v e c o l t c e p t th a t t h e o x y g e n d e f l c i t is imposed by the delay' of the rcspiratot'y arlcl circr-t-l a t o r y s y s t e m .
3.3. Ttrc liinatic,; rtf o.t.t'guI (ott.\tttttltIittn Llttrirt.g \ I t l) t' ( t t t t ( I.\' i t t t u I t'.\'c'l'r 1.rt'
F o r e x e r c i s e i t t t c r l s i t i e s e x c e e d i n g t h e t l a x i l - n a l o x y g e n c o n s u m p t i o r l . t h e k i n e t i c s o f O . L r p t a k e i s d e s c r i b e d b i t a n e c l t t a t i o n t o n l l a l l y s i m i l a r t o t h a t a p p l y i n g t b r a e r o b i c e r e r c i s e . I r l t h a t c l l s c . h o w -ever. the O. r-rptatkc tencls tclward a steady state itt t h e o v e r a l l e l t e t ' - u y r e c l r t i t ' c ' t n e t r t o 1 - th e e x e r c i s e [ ( d V O . c l t ) , ] : ( c l V O . c l t ) , - ( c l V O . d t ) , : ( c l V O . c l t ) , e t r ( l l ) w h e r e ( d V O r d t ) , . c o r r e s p o n c l s t o t h e s t e a d y s t a t e O . r - r p t a k e t h a t w o r - r l c i b e a t t a l t i e c l . w e r e it p o s s i b l e t o c a r r v c - r t - t t t h c e r e r c i s e lt l l d c r p u r e l , v a c r o b i c c o r - r c l i t i o n s . O b r i o u s l v e t l c - r t t - Q h . t h i s t e t r t a l i v e steacly' statc is ttevcl' t'citcltccJ. its thc itlcreitse irl O. uptitke cotttes tcl itt.t etlcl u hetr the nlaxit-tlal O' r-rptakc is achievccl. Scl. lbr sr.rprat'tlarit'llal exercise i n t e n s i t i e s . t h e m a x i r l l a l O . u p t a k e is t r c l - r i e v e c l i n a t i m e w h i c h i s s h o r t c r th c h i g h e r th c e r e r c i s e i n t e t r -s i t y ' . a s e x p e r i n t e t t t a l l y l o u r l d ( C r a i g " 1 9 1 2 ) .
I n l l - q r e e m e l t t w ' i t h t h e s e o b s e r v a t i o t l s . a t t h e encl of sLlpranlaxit'ttal crercise. O. r-rptake stays at i t s m a x i m a l l e v e l fb r s e v e r i t l s e c o u d s . b e c a u s e t h e c l e c r e a s e i n O . t r p t a k c id e a l l y s t a r t s fl ' o m ( d V O r d t ; , . s r - r i t i s o n l y a f t c r t h e l ' i r t u a l ( d V O , d t ) , h a s a t t a i n e d th e s L r b j e c t ' s t l l a x i m a l O ' r - r p t a k e t h a t t h e a c t L l a l ( c 1 V O . d t ) , s t i t r t s c l e c r e a s i n g . O 1 ' c o l t r s e . t h e t i n - r e a t w h i c h t l - r e v i r t r - r a l a n d t h e a c t u a l ( d V O . clt), in recovcry beconte eqr-ral is lorl-uer the hi-cher t h e e x e r c i s e i r t t e r t s i t y ( d i P r a m p e r o e t a l . . 1 9 7 3 ) .
4. Conclusions
Tl-re present analysis of the ener-qy releasc fl'otll arraerobic n-retabolistll durin-u sLlprttmaximal exer-cise and dr-rrirtg erercise tratlsietlts provides tt
re-l re-l J ['.8. tli Pt'tttrrltt'r'o. (j. Ft'r't'L'tti llt,.s:1tit'trriott I'lry.siolo.q.r 118 (lggg) l0-] tt-5
m a r k a b l c b o d y o f e l i d e n c e in sLtpport to the n o t i o n o r i g i n a l l y d e v e l o p e c l b y M a r g a r i a e t a l . ( 1 9 3 3 ) th a t t h e l a c t i c a n c l a l a c t i c o r y g e n c l e b t s " A S t h e y w ' e r e c a l l e c l " p f o v i d e all tl-re encrgv recl uirecl lbr exercise perfbrmarrce that calt-n o t b e r e l e a s e d b y aerobic metaboliscalt-nr. We h o p e t o h a v e b e e n a b l e to convince a r c a d e l t h a t . a s f i r r a s t h e a n a e r o b i c la c t i c ntetubolisr-r-r i s c o n -ccnrecl. tl-re an-ror-rr.rt ol- ener_uv that it r.eleases catr bc casili, assessed |l'om nleilsLlfentents ol- the l a t e a t r v h i c h b l o o c l l a c t i c acid changes dLrritrg e r c r c i s e . T h e h i s t o n c a l p a p e r b i , M a r g a r i a e t a l . ( 1 9 3 3 ) . a l t h o L r g h o r , r t c l a t e d f b r s e v e r a l a s p e c t s . s t r l l d e f i n e s t h e c u l t r - r r a l c o n t e x t i n w h i c h t h e s t L r d y of the c n e r g e t i c s o l - m l r s c u l a r e x e r c i s e is carriecl oLrt t l o r v r t d a l , s . p a r t i c t r l a r ' l y b y h i s s u c c e s s o f s . I t i s i r p l e a s u l e l b r u r s t c t n o t e t h e i n t p o r t a n t rolc playecl b l , P a o l o C e r r e t e l l i in tlie developntent o l ' o u r k n o w ' l e c l g e i n t h e f i c l c l s i n c e thc sixties. TIris itc-knor,vleclgentetrt is filr us thc best 'vl'a1,' of'honour--r n g h i n t o n t h e o c c a s i c t of'honour--r - of'honour--r f o r w h t c h t h i s p a p e r has b e e n w r i t t e n . References A s t n r n c l . 1 . . 1 9 6 0 . A c r o b i c r i o l k c a p a c i t r in n r c n lr n r l u r ' r n r e n u i t h s p c c i a l r c l c l e n c c 1 ( ) il g c . A c t a l ) h r s i o l . S c a n d . S u p p l . 1 6 9 . l9 ( r 0 . B i n z o n i . T . . F g ' r ' c t t i . ( i . . S c h c n l * c r ' . K . " ( ' c r . r c t c l l i . p . " l 9 g l . l ) h o s l t h t t c l c a t i t r c h t c l r o l r s i s b 1 ' r P - N \ { R i t t t l t c r t n s c t c t l ' c r . r n s t l r r . r l - l o i r r l c r e r c i s c i n h L r n t a n s . . f . A p p l . [ ) h r s i o l . 7 - ] " 16.1,1 I 6,19. B r o o k s " G . A . . 1 9 8 - 5 . ' t ' h c l i r c t u l c s h L r l t l e d L r r i n g c r e r . c i s c l n c l l c c ( ) \ ' c r \ ' . M c c l . S c i . S p o r t s E . r c r c . 1 8 . 360 -l6fi. B r o o k s . ( i . A . . D u b o r r c h u u c l . H . " B r o r i n . M . . S i c i r r - c l l o . . l . l ) . . B u t z . C ' . E . . 1 9 9 9 R o l c t t l - n t i t o c l t i ' r n c l r i u l l l r c t u t c d c h r c l r o g c -n u s c lr r . r r i l a c t i L t e o r i c l u t i o n i r r t h c i n t r a c e l l u l u r l u c t a t e s h r r t -t l c . I ) r ' o c . N a t l . A c l c l . S c i . U S A 9 6 . l l l g l l i - l . ( ' u p c l l i " c . . c l i I ) r ' a n r p c l o . P . E . " 1 9 9 5 . B l o o c l lu c t a t c l r c c u ' r u l u -t i o n i n c r c l c i s i n g I-t u n u n s . B i o c h i m . C l i n . 1 9 . 5 - + l - 5 , 1 1 . ( ' c r r c t c l l i " I ) . . I ' i i p c r ' . . 1 . . N { a n g i l i . I ' . . I l i c c i . 8 . . l 9 ( r . 1 . A c r . o b i c
l u n c l lr . u r c l o b i c u t c t l r b o l i s n r in crcr.cising t1ogs. J. Ap1tl. I ) h r s i o l 1 9 " l9 3 1 . ( ' c l l c t c l l i " I ) . . c l i P l r r n t l - r c l o . l ) . E . . I ) i i p c r . J . . 1 9 6 9 . E n c r . c v b l l l n c c o l ' i L n u c r o b i c u o l k i n t h c c l o g g i . r s t r o e u c n r i r . r s n r r r s -c l -c . A r n . . l [ ) h r s i o l . ] I 7 . 5 8 | 5 8 - 5 . ( ' c r r c t c l l i . P . t l i P l a n r l - r c l o . I ) . E . . A n r l - - r r o s o l i . ( i . . 1 9 7 1 . H i g l r e n c r g \ p h o s l " r l i l r t c r c s t n t h c s i s 1 l ' o r . n u n l c r . o b i c g l l c o l r s i s i n l ' r ' o u g a s t r o c n c l t ' r i u s n t r - r s c l c . A n t . . 1 . P h r s i o l . l l l . l 0 l I 1 0 t 6 . C ' c r r c t c l l i . P . . I ) c n r l c r g r r s t . I ) . R . . P i L g a n c l l i " W . C . . R c n t r i c " I ) . W . " 1 9 7 9 . E l ' 1 è c t s o l ' s p e c i l i c n t u s c l c t r l r i n i n g r l n \ , ' . , . - r l l t t ' c s p ( ) l t s c a n c l c r r r l r b l o t t c l l a c t u t e . . 1 . A p p l . P h r s i o l . " 1 7 . 7 6 1 7 6 1 ) C ' c r r c t c l l i . P . . c 1 i [ ) r ' t r n t p c r o . I ) . E . " 1 9 8 8 . H i g h c u c t ' g \ , p h o s p h i r t c L r t i l i z l t t i t t r t l i r t ' r i o r k 1tt'ctcluction a n c l tc n s i o r r u r l r i n t c n l n e c i n l ï o g r r t r s c l c . I' ] l l i i g . A l c h . . 1 l t 2 . ) 7 0 2 1 6 . ( ' c r r c t c l l i . P." [Jinzoni. - f . . l t ) t ) 0 . ] V I L r s c u l u l c r c r c i s c a t h i g h l r l t i t L r c l c . \ ' 1 . ' l - h c c n c l g c t i c s i s n i l l c l r n c c o l - ll r c t a t c u c c r r n t L r l i r -t i o n i n b l o o r i a t l l t i t t r d c . I n t . - l . S p o r t s M c d . l l ( S L r p p l . 1 1 . s l 7 s - 1 0 C ' r ' u i g . P . C - . . 1 9 7 1 . O r 1 ' g c n L r p t r r k c i r t t h c b c g i n n i r r g o l ' r , r o r k . . 1 . A p p l . I ) h r s i o l . i3 . ( r I I 6 l - 5 . c l i l ) n r n r p c r o . I ) . E . " N { l r g i r l i u . R . . l 9 ( r E . R c l a t i o n s h i p b e l r r c c n O . c o n s u t n l t t i o n " h i s h c u c r g \ p h o s l t l t i r t c s a n c l th c k i n c t i c s o 1 ' O . c l c b t in c r c r c i s c . I ) l 1 t i g . A l c h . 3 0 - + . l l 1 9 . c l i P r i r n t p c r o . P . E . . I ) l v i c s . C ' . T . M . . C ' c r r c t c l l r . I ) . . 1 9 7 0 , A n I r n i r l r s i s o l ' O . c l c b t c t t n t r a c l c c l i n s r r b n t i r r i n l r l c r c r c i y : . . f . A p p l . P h l s i o l . 1 9 . - i - 1 7 - 5 - t I . c l i P l l r n r p c r o . [) . F - . . I ) c c t c r s . L . . l \ , l l r r ' ' r i u ' i i r . R . . 1 9 7 - 3 . , , \ 1 1 1 c 1 1 . 1 ; . r l c b l t r n d l l r c t i c lr c i c l p r o c l L r c l i i l n l r l i c l c r h l u r s t i n s c r c r c i s c in n i u n . - 1 . A p p l P h r s i o l . l l . 6 l f l 6 l l . r l i I ) t r n t p c r o . I) . E . . M c r c r " l \ { . . C ' c r r c t c l l i . I r . . P r i p c r . J . . l 9 7 f i i L . E n c ' r - g c t i c s o l ' u n i r e r o b i c g l r c t t l r s i s i n c l o g g i r s t r o c r r c n t i L r s . P l 1 i i g . A l c h . . 1 7 7 . I E . c l i P r i r n t p c r o . I ) . F - . . f ) e n r l c r g u s t . D . R . . W i l s o n . D . W . . R c n n i c . l ) . W . . l 9 7 8 l t . B l o o c l l i r c t i c u c i r l c o n c c n t l u t i o n s i n h i g l r r c l o c i t r s u in t n r i n e . In : [ : r ' i k s s o n . I ] . . [ ; r r l b c r g . B . ( E d s . ) . S r , r i n t n t i n s N ' l c d i c i n c I \ ' . L . l n i r e ls i t r I ) r r l k [ ) r ' c s s . B u l t i n t o r - c . pp. l-19 l(r I . r l i l ) r ' l r n r p e r o . I ) . 1 - . . 1 9 8 I . H n c r ' ' r c t i c s o l ' n r r r s c u l l r l e rc r c i s c . IL c r . l ) h r s i o l . [ J i o c h c n r . [ ) h r r - n t u c o l . 8 9 . l - l - ] l l l . d i P r i r n t p c l o " P . l : . . l l o L r t c l l i c r ' . L t . " P i c t s c h . I r . . 1 9 8 3 . O r r g c n c l c l i c i t u n c l s l o r c s l r t t h c t l n s c l o l ' n t r r s c L r l a r c r e r c i s c in l r u n r t r t s . . 1 . A p p l . l ) h r s i o l . 5 - 5 " l . 1 6 l - 5 1 . d i I ) r a n r p c r o . P . E . . [ ' L r s i . S . . A u t o n L t t t ( ) . C ; . . 1 9 9 8 . I l c o n c c t t o c l r s o g l i a l r n l r c r o b i c a : L r n ' a n l r l i s i c r i t i c i r . 1 \ { c c l . S p o r ' 1 T r r r i n 5 t . i 9 - r - 1 ( x ) . F - g g l c t o n . P . . E g g l c t o n . C i . P . . lt ) 2 7 T h c i n o l g r r n i c p h o s p h u t c l r r . r c l l r l a b i l c l i r l r t r o 1 ' tl ' g i r n i c ltltosphlrtc in thc gastr()cnc-n r i u s o l ' t h e c l o g . B i o c h c n r . . 1 . I l " 1 9 0 l 9 - 5 . l r e r r c t t i . (. i . . ( i L r s s o n i . M . " c l i P n r n t l t c r o . l ) . [ . . ( ' c l l c t c l l i . l ) . . | 9 8 7 . E l - l c c t - s o l ' c r c l c i s c c t n n l r r i n t r r l i n s u r n r l r n c o L l s n t L l s c u -l u r ' 1 - r o i r c r o l ' h L r n n n s . . f . A p p l . P l r r s i o l . 6 1 . l l S E l l 9 - 1 . F i s k c . ( ' . t J . . S u b b u r o n . Y . " 1 9 1 7 . T h c l l t l L l r e o t ' i n o r g u n i c p h o s p h r r t e i n t h c v o l r r r r t i r r l , n t r r s c l c . S c i c n c e 6 - 5 " , 1 0 1 - 1 0 . 1 . ( i i s o l l l " l- . . R o b i n s o n . S . . T L r r r e l l . E . S . . 1 9 6 6 . E l l è c t s o l - a e r o b i c u o l k p e r l i r n l c c l c l r . r r i n g r c c o v e t ' \ 1 l ' o n i c r l t a u s t i n g u o r k . l A p p l . P h l s i o l . l l . 1 7 6 7 l l l 2 . ( j r a s s i . 8 . . I - c r r c t t i . ( i . . K a 1 s e r . B . . M i r r z o l u t i . M . " C - r t l o n t b i n i . , A . . M i r r c o n i . ( - . " C - c r r c t c l l i . I ) . " 1 9 9 5 . M l r r i n t a l r - r r t c o l ' b l o o c l ll L c t u t c u c c u r n u l l t i o r r d u r i n g c x c r c i s e u t a l t i t u c l c i n l r u n . r u r r s . . l . , A p p l . P h r s i o l . 7 9 . 3 3 1 i - 1 9 . I I c r r r r " I r . M . . l 9 - 5 l . A c r o b i c o : i 1 g c n c o n s r _ r r t r l t t i o t r a n c l u l a c t i c r l c b t i n n r u s c L r l a r r . i o r k . . 1 . A p p l . P h l s i o l . 3 " - l l 7 . 1 3 8 . H c t ' n . t r r n s c n " L . . l 9 l I . L l r c t u t e p l o c l u c l i t t n t l u r i n g c x c r c i s c . l n : P e r n o u " B . 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