Journal of Applied Physiology
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J Appl Physiol (May 23, 2003). doi:10.1152/japplphysiol.01118.2002
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Submitted on December 4, 2002
Accepted on May 7, 2003

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

Kristen D Dawson1, Krista R Howarth1, Mark A Tarnopolsky2, Nathan D Wong1, and Martin J Gibala1*

1 Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada
2 Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada; Exercise Metabolism Research Group, Department of Medicine (Neurology and Rehabilitation), McMaster University, Hamilton, Ontario, Canada

* To whom correspondence should be addressed. E-mail: gibalam{at}mcmaster.ca.

Muscle glycogenolytic flux and lactate accumulation during exercise are lower after 3-7 d of "short-term" aerobic training (STT) in men (e.g., Green et al., J. Appl. Physiol. 72:484-491, 1992). We hypothesized that 5 d of STT would attenuate pyruvate production and the increase in muscle tricarboxylic acid cycle intermediates (TCAI) during exercise, due to reduced flux through the alanine aminotransferase reaction (AAT; pyruvate + glutamate <-> 2-oxoglutarate + alanine). Eight women (22±1 y, VO2peak = 40.3±4.6 ml[[rad]]kg-1[[rad]]min-1) performed 7 x 45 min bouts of cycle exercise @ 70% VO2peak over 9 d (one bout[[rad]]d-1; rest only on d 2 and 8). During the first and last bouts, biopsies (v. lateralis) were obtained at rest and after 5 and 45 min of exercise. Muscle [glycogen] was ~50% higher at rest after STT (493±38 vs 330±20 mmol[[rad]]kg-1 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 4 measured TCAI was 40% lower (P<=0.05) during exercise after training (1.68±0.60 vs 2.71±0.44 mmol[[rad]]kg-1 dry wt.) and the net decrease in [glutamate] was attenuated (P<=0.05) We conclude that (i) the contraction-induced increase in flux through AAT is reduced after 5 d of aerobic training, and (ii) the muscle glycogenolytic response during exercise after STT in women is similar to that shown in men.




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