A Single Bout of Aerobic Exercise Compromises Down-regulation of MuRF Expression Subsequent to Resistance Exercise

Abstract

While many athletes incorporate both aerobic and resistance exercise in their training regimen, the compatibility of these two exercise modes, each offering a very specific stimulus, has been challenged. Thus, it has been inferred that skeletal muscle adaptations, typical of resistance training, may be hampered if preceded by aerobic exercise. PURPOSE: To explore the effects of acute concurrent aerobic and resistance exercise on molecular markers fundamental to resistance exercise-specific muscle adaptations. METHODS: Nine physically active men (23±2 yrs, 181±6 cm, 75±6 kg) were subjected to an unilateral exercise model over three non-consecutive exercise days within a week, such that one limb was assigned to concurrent knee extensor exercise (AE+RE) and the other limb performed resistance exercise (RE) only. In the morning of each day of exercise, subjects performed ∼45 min unilateral endurance exercise (heart rate and plasma lactate concentration, respectively averaged 162 bpm and 5.7 mmol/l at completion) on a modified cycle ergometer. Six hrs later, unilateral resistance exercise (4 sets of 7 reps of leg press and knee extension) of either limb was performed employing flywheel ergometers. Muscle power of each rep and set was measured. Percutaneous muscle biopsies were obtained from m.vastus lateralis immediately before (PRE), 15 min (POST1) and 3 hrs (POST2) after the final resistance exercise bout. Levels of mRNA of VEGF and PGC-1α were used as endurance markers, and MuRF as a marker for protein regulation. VEGF, PGC-1α and MuRF were measured using RT-PCR and analyzed using ANOVA for repeated measures with a 5% α-level. RESULTS: Peak power (averaged across all days of exercise) was similar (p>0.05) for AE+RE and RE in both the leg press (mean±SE; 233±16 vs. 247±17 W) and the knee extension (342±20 vs. 357±20 W) exercise. Glycogen content was lower in AE+RE than RE (p<0.05). VEGF and PGC-1α mRNA-levels were two- and four-fold higher in AE+RE compared with RE both before (PRE) and after (POST1, POST2) resistance exercise (p<0.05). MuRF expression decreased (25%; p<0.05) after RE, but not after AE+RE (p>0.05). CONCLUSIONS: When performing resistance exercise subsequent to aerobic exercise on the same day, it appears important steps regulating protein turnover in response to resistance exercise are compromised.