Effects of Preexercise Feeding on Markers of Satellite Cell Activation

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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 ± SD: age = 22 ± 4 yr, body mass = 77.8 ± 8.3 kg, percent body fat = 17.8 ± 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 < 0.05), 2) CDK4 expression increased at 6 h (+86%, P < 0.05), 3) MYOD expression increased at 6 h (+98%, P < 0.05), 4) P27KIP1 expression decreased at 2 h (−35%, P < 0.05) and 6 h (−59%, P < 0.001), and 5) P21CIP1 expression substantially increased 2 and 6 h postexercise (+1.250% and +4.670%, respectively, P < 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.

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