It has been proposed that protein supplementation during resistance exercise 
training enhances muscle hypertrophy. The degree of hypertrophy during training 
is controlled in part through the activation of satellite cells and myonuclear 
accretion.
PURPOSE: This study aimed to determine the efficacy of protein supplementation 
(and the type of protein) during traditional resistance training on myofiber 
cross-sectional area, satellite cell content, and myonuclear addition.
METHODS: Healthy young men participated in supervised whole-body progressive 
resistance training 3 d·wk for 12 wk. Participants were randomized to one of 
three groups ingesting a daily 22-g macronutrient dose of soy-dairy protein 
blend (PB, n = 22), whey protein isolate (WP, n = 15), or an isocaloric 
maltodextrin placebo (MDP, n = 17). Lean mass, vastus lateralis 
myofiber-type-specific cross-sectional area, satellite cell content, and 
myonuclear addition were assessed before and after resistance training.
RESULTS: PB and the pooled protein treatments (PB + WP = PRO) exhibited a 
greater whole-body lean mass %change compared with MDP (P = 0.057 for PB) and (P 
= 0.050 for PRO), respectively. All treatments demonstrated similar leg muscle 
hypertrophy and vastus lateralis myofiber-type-specific cross-sectional area (P 
< 0.05). Increases in myosin heavy chain I and II myofiber satellite cell 
content and myonuclei content were also detected after exercise training (P < 
0.05).
CONCLUSION: Protein supplementation during resistance training has a modest 
effect on whole-body lean mass as compared with exercise training without 
protein supplementation, and there was no effect on any outcome between protein 
supplement types (blend vs whey). However, protein supplementation did not 
enhance resistance exercise-induced increases in myofiber hypertrophy, satellite 
cell content, or myonuclear addition in young healthy men. We propose that as 
long as protein intake is adequate during muscle overload, the adaptations in 
muscle growth and function will not be influenced by protein supplementation.