Within-subject Comparison Reveals Enhanced Satellite Cell Response To Eccentric Overload During Heavy Resistance Exercise

Satellite cells (SC) play a crucial role in muscle regeneration and hypertrophy. For SC activation, eccentric muscle contractions seem to be most effective. PURPOSE: to find out if heavy concentric/eccentric resistance exercise (CON/ECC) with eccentric overload (CON/ECC+) induces a greater SC response than CON/ECC in a within-subject comparison to eliminate the effects of inter-individual variability in muscular adaptation. METHODS: 23 recreationally strength-trained male subjects (24.7 ± 4 yr, 182 ± 5.3 cm, 81 ± 8.2 kg) performed one bout of exhaustive leg extension exercise as CON/ECC+ with one leg and one bout of equivalent CON/ECC with the contra-lateral leg on the same occasion in randomized order. Isokinetic and isometric strength tests were performed for both legs separately 2 weeks prior and on the first 3 days after exercise. Biopsies from the vastus lateralis of both legs were obtained in rested condition 7 days before and 7 days after the resistance exercise. Immunohistochemical analyses of cryosections were conducted for total SC number (SCtot) and SC related to myofiber types (Pax7/MHCII/Laminin/DAPI). RESULTS: Two-way repeated measures ANOVA revealed significantly (p = 0.000) greater increases in SCtot, SCtypeI and SCtypeII after CON/ECC+ [SCtot: 0.054 ± 0.026 to 0.120 ± 0.050 (122.2 %), p = 0.000, SCtypeI: 0.057 ± 0.029 to 0.123 ± 0.062 (115.8 %), p = 0.000, SCtypII: 0.050 ± 0.029 to 0.121 ± 0.060 (142 %), p = 0.000] compared with CON/ECC [SCtot: 0.054 ± 0.023 to 0.071 ± 0.037 (31.5 %), p = 0.035, SCtypeI: 0.061 ± 0.035 to 0.070 ± 0.045 (14.8 %), p = 0.369, SCtypII: 0.040 ± 0.031 to 0.076 ± 0.037 (90 %), p = 0.001]. Central myonuclei count per fiber was significantly increased after CON/ECC+ (0.010 ± 0.009 vs. 0.024 ± 0.024, p = 0.011) and CON/ECC (0.009 ± 0.012 vs. 0.016 ± 0.015, p = 0.042). There was a similar significant decrease in maximum strength after CON/ECC+ and CON/ECC. The decrease was not significantly correlated with ΔSC. CONCLUSION: Apparently, exhaustive CON/ECC+ is superior to equivalent CON/ECC for the induction of a significant SC response. However, the lack of a significant correlation between the increases in SCs and the loss of maximum strength as well as the comparable increase in central myonuclei count indicate similar myofiber damage and regeneration processes after CON/ECC+ and CON/ECC.