EFFECTS OF AEROBIC TRAINING ON HUMAN SKELETAL MUSCLE METABOLISM DURING SUBMAXIMAL EXERCISE

Abstract

Fuel utilization in skeletal muscle during exercise shifts from carbohydrate to fat with aerobic training. Glycogen phosphorylase (Phos) and pyruvate dehydrogenase (PDH) play major roles in regulating carbohydrate flux in skeletal muscle, however, the mechanisms which regulate their activity in skeletal muscle after aerobic training are unclear. PURPOSE To determine the mechanism of regulation of Phos and PDH during exercise in trained skeletal muscle. METHODS Eight healthy male subjects exercised at the same absolute workload (206 ± 5 W) on two occasions on a cycling ergometer for 15 min before (Pre) and after (Post) 7 weeks of aerobic cycle training. Muscle biopsies were taken at rest and after 5 and 15 min of exercise. Activities of the more active form of Phos (Phos a) and the activated form of PDH (PDHa) were measured, along with muscle concentrations of glycogen, glycolytic intermediates, lactate, and high energy phosphates. Training comparisons were made using two-way ANOVA. RESULTS After 15 min of exercise, PDHa activity was reduced in Post (2.7 ± 0.4 (3.7 ± 0.5 mmol/kg wet wt/min), as was glycogen utilization (7.4 ± 1.3 vs. 13.2 ± 1.0 mmol/kg dry wt/min), lactate (21.4 ± 3.3 vs. 72.8 ± 9.3 mmol/kg dry wt) and pyruvate (0.46 ± 0.03 vs. 0.94 ± 0.14 mmol/kg dry wt) accumulation, and calculated free [ADP] (84 ± 10 vs. 111 ± 16 (mol/kg dry wt). In addition, no change in Phos a was seen (Pre, 38.8 ± 2.5; Post, 46.8 ± 2.4 % mole fraction of Phos a). CONCLUSIONS Training resulted in reduced muscle glycogenolysis, through post-transformational regulation of Phos a by free ADP. There was also a reduced flux through PDH due to reduced pyruvate availability. As a result, less lactate accumulated due to a better match between pyruvate production and oxidation. Supported by CIHR (GJFH) and OGS (PJL).