Regulators of Muscle Hypertrophy are Unaffected by Whey Protein and Casein Supplementation in Older Individuals

PURPOSE: To compare whey and casein protein combined with a 12-week resistance training program on systemic and cellular mechanisms regulating skeletal muscle hypertrophy in older males. METHODS: Thirty-six non-resistance trained males (62.5±6.8 yrs, 177±6.32 cm, 95.25±16.9 kg) were randomized in a double blind manner to ingest either whey protein (WP) [20g/d WP + 5g carbohydrate (CHO)], casein protein (CAS) (20g/d CAS + 5g CHO) or maltodextrose placebo (CHO) [25g/d CHO] while participating in a supervised high intensity resistance training program (3 sets x 10 repetitions at 75% of 1RM), 3 days per week for 12 weeks. Testing sessions were completed prior to (0 weeks), 4 weeks, 8 weeks and 12 weeks post resistance training and supplementation. Each testing session included blood collection and vastus lateralis muscle biopsy. The blood serum was analyzed for insulin-like growth factor 1 (IGF-1), free testosterone and hepatocyte growth factor (HGF) and the muscle tissue for phosphorylated mesenchymal-epithelial transition factor (c-Met). Data was analyzed using repeated measures ANOVA. RESULTS: A significant time effect was observed for serum free testosterone (0 weeks:14.26±9.78pg/ml vs. 12 weeks: 17.01±13.10pg/ml, p<0.05), with subsequent post-hoc analysis revealing significantly higher serum free testosterone levels at 4 weeks (18.61±15.20pg/ml, p=0.021) and 8 weeks (17.67±14.04pg/ml, p=0.028) compared to 0 weeks (14.26±9.78pg/ml). No time effects were evident for serum IGF-1 (0 weeks:0.841±0.487pg/ml vs. 12 weeks:0.824±0.448pg/ml, p=0.309), HGF (0 weeks:332.33±705.17pg/ml vs. 12 weeks:306.52±586.03pg/ml, p=0.483), or phosphorylated c-Met (0 weeks:0.109±0.242ng/mg vs. 12 weeks:0.038±0.039ng/mg, p=0.316). A significant group effect was observed for serum IGF-1 (p<0.05), with subsequent post-hoc analysis revealing significantly higher serum IGF-1 levels in the WP (0.684±0.381, p<0.05) and CAS groups (0.925±0.437, p<0.01) compared to CHO placebo (0.353±0.267). No other group or group by time interactions were observed. CONCLUSIONS: Whey protein and casein supplementation in conjunction with 12-weeks of resistance training were unable to enhance serum IGF-1 and testosterone levels and/or markers of satellite cell activation in older males.