Effects of preexercise feeding on markers of satellite cell activation

Purpose: The purpose of this study was to determine if consuming isoenergetic (25 g) doses of carbohydrate or protein versus a noncaloric placebo before conventional resistance training affected the myogenic expression of cell cycle–regulating genes as well as the muscle [DNA] acutely after exercise. Methods: Ten untrained men (mean T SD: age = 22 T 4 yr, body mass = 77.8 T 8.3 kg, percent body fat = 17.8 T 4.0) participated in three resistance exercise sessions (three sets of 10 repetitions at 80% one-repetition maximum for the bilateral hack squat, leg press, and leg extension exercises) in a crossover fashion, which were preceded by carbohydrate, protein, or placebo ingestion 30 min before training. Presupplement/preexercise and 2- and 6-h postexercise muscle biopsies were obtained during each session and analyzed for fold changes in CDK4, CYCLIN D1, MGF, MYOD, P21CIP1, and P27KIP1 messenger RNA expression using real-time reverse transcriptase-polymerase chain reaction as well as muscle [DNA] using cuvette-based fluorometric methods. Results: Nonparametric statistics were completed, and no conditions _ time interaction effects were revealed. Several exercise-mediated responses were found to occur independent of condition: 1) muscle [DNA] increased at 6 h (+40%, P G 0.05), 2) CDK4 expression increased at 6 h (+86%, P G 0.05), 3) MYOD expression increased at 6 h (+98%, P G 0.05), 4) P27KIP1 expression decreased at 2 h (j35%, P G 0.05) and 6 h (j59%, P G 0.001), and 5) P21CIP1 expression substantially increased 2 and 6 h postexercise (+1.250% and +4.670%, respectively, P G 0.001). Conclusions: The tandem DNA and cell cycle regulator gene expression analyses provide preliminary evidence to suggest that satellite cell activation and proliferation may be occurring at early postexercise time points after a conventional resistance exercise bout, a phenomenon that may seemingly be independent of preexercise macronutrient ingestion.