Effects of 16 weeks of two different high-protein diets with either resistance or concurrent training on body composition, muscular strength and performance, and markers of liver and kidney function in resistance-trained males

PURPOSE: It is unclear whether resistance (RT) and concurrent training (CT; resistance plus endurance training) combined with different protein intakes have differential effects on muscle hypertrophy, strength, and performance. Therefore, we compared the effects of two high-protein diets (1.6 or 3.2 g.kg(−1.)d(−1)) during 16 weeks of either CT or RT alone in resistance-trained males. METHODS: Forty-eight resistance-trained males (age: 26 ± 6 yr, body mass index: 25.6 ± 2.9 kg.m(−2)) performed 16 weeks (four sessions·w(−1)) of CT or RT with either 1.6 g.kg(−1.)d(−1) protein (CT1; n = 12; RT1; n = 12) or 3.2 g.kg(−1.)d(−1) protein (CT2; n = 12; RT2; n = 12). Training adaptations were assessed pre-, mid-, and post-intervention. RESULTS: All measures of performance (endurance, vertical jump, and pull-up), lean mass, muscle strength, and power significantly increased post-intervention in all groups, but peak power gains were greater in RT2 compared with RT1 and CT1 (p < .05). VO(2max) significantly increased in both CT groups (p < .001). Select biochemical markers of kidney and liver function significantly increased within the RT2 and CT2 groups (p < .05), however, no between-group differences were apparent (p > .05). CONCLUSIONS: With the exception of peak power, intake of 1.6 g.kg(−1.)d(−1) of protein appears sufficient to maximize gains in lean mass, muscle strength, performance, and aerobic capacity during both RT and CT without influencing markers of kidney and liver function, indicating this daily protein amount is effective and safely tolerated in young, healthy adults.