Sex-based Differences Following Eccentric Exercise-induced Muscle Damage

The response to skeletal muscle damage may be different between males and females with sex hormones proposed to be an underlying factor. Satellite cells (SC) are essential for muscle regeneration after damaging exercise with early indications suggesting a blunted response in females. PURPOSE: We aimed to comprehensively characterize the damage and SC response to eccentric exercise-induced damage in males and females. Further, we aimed to determine if possible sex differences may be attributed to levels of 17β-estradiol. METHODS: Thirty healthy males and females (21 ± 3 years [mean ± SD]) undertook 300 (30 x 10) maximal eccentric leg extension contractions on an isokinetic dynamometer, and measures were collected prior to and at six time points after exercise. Biopsies from the vastus lateralis were collected for immunohistochemical analyses. Ultrasound sonography was used to determine muscle thickness (proxy measure of swelling) and blood concentrations of 17β-estradiol and creatine kinase (CK) were determined. Measures of strength and subjective soreness were also collected. RESULTS: We observed an interaction in the CK response demonstrating a peak at 24 h (M: 536 ± 109 U/L, F: 415 ± 79 U/L); this remained elevated in males over 120 h while females returned to baseline (p < 0.05). Satellite cell content in type II fibers peaked at 72 h in males (10.1 ± 3.0 Pax7+ cells/100 fibers; p < 0.05), but the same expansion was not observed in females. An interaction was detected for muscle thickness peaking at 48 h in males (2.90 ± 0.35 cm) while females peaked instead at 72 h (2.47 ± 0.25 cm). Strength decreased significantly in both groups but was restored to baseline in males at 5 h onwards, while females only recovered at 120 h. No measures were associated with changes in circulating levels of 17β-estradiol. CONCLUSION: A sexual dimorphism in the SC response to damaging exercise was evident between males and females but was not associated with circulating 17β-estradiol.