Introduction: The hypothesis that brief intermittent exercise-induced increases in human skeletal muscle metabolic mRNA is dependent on relative workload was investigated.
Methods: Trained (n = 10) and untrained (n = 8) subjects performed exhaustive intermittent cycling exercise (4 × 4 min at 85% of V˙O2peak, interspersed by 3 min). Trained subjects also performed the intermittent exercise at the same absolute workload as the untrained subjects, corresponding to 70% of V˙O2peak (n = 6).
Results: Exercise at 85% of V˙O2peak elevated (P < 0.001) venous plasma lactate to 10.1 ± 0.4 and 10.8 ± 0.5 mM in the trained and untrained subjects, respectively. Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) mRNA expression was increased (P < 0.001) approximately four- to fivefold for several hours after exercise in both groups. After exercise at 70% of V˙O2peak, venous plasma lactate was less (P < 0.001) elevated (3.1 ± 0.7 mM) and PGC-1α mRNA content was less (P < 0.05) increased (approximately threefold) than after exercise at 85% of V˙O2peak. Likewise, pyruvate dehydrogenase kinase 4 and hexokinase II mRNA expressions were increased (P < 0.05) only after exercise performed at 85% of V˙O2peak in the trained subjects. Hypoxia-inducible factor 2α mRNA only increased (P < 0.05) 3 h into recovery in trained subjects, with no difference between the 70% and 85% of V˙O2peak trial. No change in hypoxia-inducible factor 1α, phosphofructokinase, citrate synthase, or lactate dehydrogenase, heart and muscle isoforms, mRNA expressions was detected after any of the exercise trials.
Conclusions: The relative intensity of brief intermittent exercise is of major importance for the exercise-induced increase of several mRNA, including PGC-1α.