Muscle Injury, Strength And Redox Responses Following Exercise In Individuals With Different Satellite Cell Content

Satellite cells (SC) are indispensable for muscle regeneration and growth. It has been suggested that skeletal muscle recovery and growth are related to its basal SC content. However, there is no evidence regarding the influence of SC content on muscle damage, strength and redox responses following aseptic muscle injury in humans. PURPOSE: To determine whether basal SC content affects muscle injury, strength and redox responses following exercise-induced muscle damage. METHODS: Twenty-four men (22.5 + 2.2 years) underwent a baseline biopsy sampling of the vastus lateralis muscle and were stratified into a low or high group based on their SC content (pax7 + Low vs. pax7 + High group). Afterward, participants completed an intense exercise protocol (300 maximal eccentric contractions of the quadriceps muscle) aiming at inducing skeletal muscle damage. Muscle injury and strength markers were measured and blood sampling was performed at baseline, as well as at 2- and 8-days post-exercise. During the study, participants followed a balanced diet and abstained from exercise. RESULTS: Creatine kinase (CK) increased in the low group, only at 2D (21-fold, p < 0.001). In the high group, CK increased throughout recovery (2D: 17.6-fold, p < 0.001; 8D: 7.9-fold, p = 0.047). Muscle soreness (DOMS) increased in both groups at 2D (low: 7.4-fold; high: 6.5-fold; all p < 0.001) and 8D (low: 1.6-fold, p < 0.001; high: 1.1-fold, p = 0.006). At 2D, the high group exhibited a lower increase in DOMS compared to the low group (p = 0.028). Eccentric peak torque decreased in both groups only at 2D (low: -42%, p < 0.001; high: -30%, p = 0.004). Reduced/oxidized glutathione (GSH/GSSG) ratio decreased in both groups only at 2D (low: -61%; high: -48%, all p < 0.001). The high group displayed a higher GSH/GSSG ratio at all time points compared to the low group (p < 0.05). Protein carbonyls (PC) increased in both groups throughout recovery (2D: low, 2.8-fold, p < 0.001; high, 2.7-fold, p = 0.001; 8D: low, 1.2-fold, p = 0.002; high, 1.7-fold, p = 0.005) with no between-group differences. CONCLUSION: Damaging exercise increases muscle injury markers and decreases strength and redox status irrespective of SC content in human skeletal muscle. Higher SC content is associated with lower levels of DOMS during the initial phase of recovery.