Resistance exercise-induced increase in muscle mass correlates with p70S6 kinase phosphorylation in human subjects

The purpose of the present study was to investigate the possible relationship between a change in Thr³⁸⁹ phosphorylation of p70S6 kinase (p70^S6k) after a single resistance training session and an increase in skeletal muscle mass following short-term resistance training. Eight male subjects performed an initial resistance training session in leg press, six sets of 6RM with 2 min between sets. Muscle biopsies were obtained from the vastus lateralis before (T1) and 30 min after the initial training session (T2). Six of these subjects completed a 14-week resistance-training programme, three times per week (nine exercises, six sets, 6RM). A third muscle biopsy was obtained at the end of the 14-week training period (T3). One repetition maximum (1RM) squat, bench press and leg press strength as well as fat-free mass (FFM, with dual energy X-ray absorptiometry) were determined at T1 and T3. The results show that the increase in Thr³⁸⁹ phosphorylation of p70^S6k after the initial training session was closely correlated with the percentage increase in whole body FFM (r = 0.89, P < 0.01), FFM_leg (r = 0.81, P < 0.05), 1RM squat (r = 0.84, P < 0.05), and type IIA muscle fibre cross sectional area (r = 0.82, P < 0.05) after 14 weeks of resistance training. These results may suggest that p70^S6k phosphorylation is involved in the signalling events leading to an increase in protein accretion in human skeletal muscle following resistance training, at least during the initial training period.