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Short-term training attenuates muscle TCA cycle expansion during exercise in women

¹Exercise Metabolism Research Group, Department of Kinesiology, and ²Departments of Neurology and Rehabilitation, Department of Medicine, McMaster University, Hamilton, Ontario, Canada L8S 4K1

Submitted 4 December 2002 ; accepted in final form 7 May 2003

Muscle glycogenolytic flux and lactate accumulation during exercise are lower after 3-7 days of "short-term" aerobic training (STT) in men (e.g., Green HJ, Helyar R, Ball-Burnett M, Kowalchuk N, Symon S, and Farrance B. J Appl Physiol 72: 484-491, 1992). We hypothesized that 5 days of STT would attenuate pyruvate production and the increase in muscle tricarboxylic acid cycle intermediates (TCAI) during exercise, because of reduced flux through the reaction catalyzed by alanine aminotransferase (AAT; pyruvate + glutamate 2-oxoglutarate + alanine). Eight women [22 ± 1 yr, peak oxygen uptake (O_{2 peak}) = 40.3 ± 4.6 ml · kg^-1 · min^-1] performed seven 45-min bouts of cycle exercise at 70% O_{2 peak} over 9 days (1 bout/day; rest only on days 2 and 8). During the first and last bouts, biopsies (vastus lateralis) were obtained at rest and after 5 and 45 min of exercise. Muscle glycogen concentration was 50% higher at rest after STT (493 ± 38 vs. 330 ± 20 mmol/kg dry wt; P 0.05), and net glycogenolysis and lactate accumulation were reduced after 5 min of exercise by 59 and 49%, respectively (P 0.05). The net increase in four measured TCAI was 40% lower (P 0.05) during exercise after training (1.68 ± 0.60 vs. 2.71 ± 0.44 mmol/kg dry wt), and the net decrease in glutamate concentration was attenuated (P 0.05). We conclude that 1) the contraction-induced increase in flux through AAT is reduced after 5 days of aerobic training and 2) the muscle glycogenolytic response during exercise after STT in women is similar to that in men.

metabolic regulation; glycogen; lactate; tricarboxylic acid cycle

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