Background:Satellite cells are normally quiescent, myogenic stem cells located between the basement and plasma membrane. The proliferation and differentiation of satellite cells, as well as their fusion with existing myofibers, are key events leading to the process of muscular hypertrophy. Acute settings of resistance training have been shown to stimulate both muscle protein synthesis and quiescent satellite cell proliferation. However, it is still not known which of these processes is more important to long-term exercise-induced hypertrophy observed with regular resistance activity. Studies have demonstrated that 1 bout of exercise can increase satellite cell proliferation as well as genes required for satellite cell activity (eg, cyclins, cyclin-dependent kinases [cdks], cdk-inhibitors, and myogenic regulatory factors [MRFs]) with or without macronutrient consumption. However, no research to date has examined the effects of concomitant resistance exercise and macronutrient ingestion on early post-exercise events (ie, within 6 to 8 hours) indicative of satellite cell activity.

Hypothesis:Compared with pre-exercise ingestion of noncaloric placebo (PLC), ingestion of isoenergetic doses of carbohydrate (CHO) or protein (PRO) would affect myogenic expression of cell-cycle regulatory genes and muscle DNA synthesis in skeletal muscle from young males 2 and 6 hours after a conventional resistance training bout.

Subjects:10 untrained, healthy men (mean ± standard deviation: age 22 ± 4 years; weight 77.8 ± 8.3 kg; body fat 17.8% ± 4%) participated in the study.

Experimental design:Single-blinded, placebo-controlled, cross-over

Treatments and protocol: After several familiarization sessions, subjects participated in 3 resistance exercise sessions in which they completed 3 sets of 10 concentric-eccentric repetitions of bilateral leg press, hack squat, and leg extension exercises at a lifting intensity of 80% 1-repetition max (1RM) with 2 min rest between sets and exercises. Subjects randomly ingested isoenergetic doses (25 g) of CHO (maltodextrin), PRO (whey isolate), or PLC (artificially sweetened water) 30 min before each exercise session. Muscle biopsies were obtained from the vastus lateralis pre-exercise and 2- and 6-hours post-exercise and analyzed for fold changes in CDK4, CYCLIN D1, MGF, MYOD, P21CIP1 , and P27KIP1 mRNA expression using real-reverse-transcriptase polymerase chain reaction (RT-PCR), and for muscle DNA concentration using cuvette-based fluorometric methods.