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Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
The purpose of this study was to
investigate the hypothesis that a single, extended session of heavy
exercise would be effective in inducing adaptations in energy
metabolism during exercise in the absence of increases in oxidative
potential. Ten healthy males [maximal aerobic power
(
O2 peak) = 43.4 ± 2.2 (SE)
ml · kg
1 · min1]
participated in a 16-h training session involving cycling for 6 min
each hour at ~90% of maximal oxygen consumption. Measurements of
metabolic changes were made on tissue extracted from the vastus lateralis during a two-stage standardized submaximal cycle protocol before (Pre) and 36-48 h after (Post) the training session. At Pre, creatine phosphate (PCr) declined (P < 0.05)
by 32% from 0 to 3 min and then remained stable until 20 min of
exercise at 60%
O2 peak before
declining (P < 0.05) by a further 35% during 20 min of
exercise at 75%
O2 peak.
Muscle lactate (mmol/kg dry wt) progressively increased (P < 0.05) from 4.59 ± 0.64 at 0 min to 17.8 ± 2.7 and 30.9 ± 5.3 at 3 and 40 min, respectively, whereas muscle glycogen (mmol glucosyl
units/kg dry wt) declined (P < 0.05) from a rest value of 360 ± 24 to 276 ± 31 and 178 ± 36 at similar time points. During
exercise after the training session, PCr and glycogen were not as
depressed (P < 0.05), and increases in muscle lactate were
blunted (P < 0.05). All of these changes occurred in the
absence of increases in oxidative potential as measured by the maximal
activities of citrate synthase and malate dehydrogenase. These findings
are consistent with other studies, namely, that muscle metabolic
adaptations to regular exercise are an early adaptive event that occurs
before increases in oxidative potential.
oxidative potential; enzymes; metabolites; metabolic control
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