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

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 ((V)over dotO(2 peak)) = 40.3 +/- 4.6 ml.kg(-1).min(-1)] performed seven 45-min bouts of cycle exercise at 70% (V)over dotO(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 similar to50% higher at rest after STT (493 +/- 38 vs. 330 +/- 20 mmol/kg dry wt; P less than or equal to 0.05), and net glycogenolysis and lactate accumulation were reduced after 5 min of exercise by 59 and 49%, respectively (P less than or equal to 0.05). The net increase in four measured TCAI was similar to40% lower (P less than or equal to 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 less than or equal to 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.