It is unclear whether protein supplementation augments the gains in muscle strength and size observed after resistance training (RT) because limitations to previous studies include small cohorts, imprecise measures of muscle size and strength, and no control of prior exercise or habitual protein intake. We aimed to determine whether whey protein supplementation affected RT-induced changes in elbow flexor muscle strength and size.
We pair-matched 33 previously untrained, healthy young men for their habitual protein intake and strength response to 3-wk RT without nutritional supplementation (followed by 6 wk of no training) and then randomly assigned them to protein (PRO, n = 17) or placebo (PLA, n = 16) groups. Participants subsequently performed elbow flexor RT 3 d · wk(-1) for 12 wk and consumed PRO or PLA immediately before and after each training session. We assessed elbow flexor muscle strength (unilateral 1-repetition maximum and isometric maximum voluntary force) and size (total volume and maximum anatomical cross-sectional area determined with magnetic resonance imaging) before and after the 12-wk RT.
PRO and PLA demonstrated similar increases in muscle volume (PRO 17.0% ± 7.1% vs PLA 14.9% ± 4.6%, P = 0.32), anatomical cross-sectional area (PRO 16.2% ± 7.1% vs PLA 15.6% ± 4.4%, P = 0.80), 1-repetition maximum (PRO 41.8% ± 21.2% vs PLA 41.4% ± 19.9%, P = 0.97), and maximum voluntary force (PRO 12.0% ± 9.9% vs PLA 14.5% ± 8.3%, P = 0.43).
In the context of this study, protein supplementation did not augment elbow flexor muscle strength and size changes that occurred after 12 wk of RT.