Protein Supplementation Does Not Affect Myogenic Adaptations to Resistance Training

Abstract

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.

Trial registration: ClinicalTrials.gov NCT01749189.

Conflict of interest statement

Conflicts of Interest

PTR, MSB, RRD, SI, MBC, RM, KJ, EV, BBR have no conflicts of interest.

The authors declare that this study was funded by Dupont Nutrition & Health. Representatives from Dupont Nutrition & Health were not involved with data collection and laboratory analysis

The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the present study do not constitute endorsement by ACSM.

Figures

Figure 1

Fiber-type specific and mean (MFA) vastus lateralis cross-sectional area by treatment. Protein blend (PB) or whey protein (WP) or maltodextrin placebo (MDP) and representative immunohistochemical image for identification of fiber typing and cross-sectional area quantification in vastus lateralis. MHC I stained purple (top left), MHC IIa stained green (top right), and MHC type IIx stained red (bottom right) and merged image (bottom left).Data are mean ± SEM, n=15 (WP), 22 (PB) & 17 (MDP). Units are µm2. Significant change * (p<0.05).

Figure 2

Vastus lateralis fiber-type specific satellite cell content, myonuclei and myonuclear domain by treatment and representative immunohistochemical image for fiber-type specific identification of Pax7 positive satellite cells and myonuclei. DAPI positive nuclei stained blue (top left), Pax7+ cells stained yellow (top right), laminin basement membrane stained red (middle left), MHC I stained purple and MHC II black - negative staining (middle right) and merged image with arrows highlighting Pax7+ satellite cells (bottom). Protein blend (PB), whey protein (WP) or maltodextrin placebo (MDP). Data are mean ± SEM, n=15 (WP), 22 (PB), 17 (MDP) & 37 (PRO). Units are µ2/myonucleus. * (p<0.05), # (p<0.10) vs pre within that group, main effect of exercise is denoted as a bar across both treatments. PRO (p<0.05) for change in pooled protein group vs pre. PRO > MDP & (p=0.073) via ANCOVA.

Figure 3

Myosin heavy chain composition (MHC) in the vastus lateralis expressed as relative frequency. PRO indicates an effect of the pooled protein treatments to increase over pre. Significant change vs. pre * (p<0.05). Bar indicates an exercise effect.