Effect of a work‐matched bout of lengthening or shortening contractions on satellite cell proliferation in human muscle

Purpose To determine the extent of satellite cell (SC) activity following a work‐matched bout of lengthening (LC) or shortening (SHC) contractions. Methods Participants (aged 22.6 ± 1.5 years) were assigned to either LC (n=6) or SHC (n=6). A control muscle biopsy was taken from the non‐exercised leg prior to exercise. Subjects performed a bout of unilateral LC or SHC of the knee extensors. A biopsy was obtained from the exercised leg 24 h after exercise. Muscle soreness and strength were assessed pre‐, immediately post‐exercise, and every 24 h for 4 d. Immunohistochemistry was used to quantify total and fiber‐type specific SC content from exercised and control legs in LC and SHC. Repeated‐measures ANOVA (p<0.05) was used to analyze data. Results Participants performed 40.8 ± 2.9 KJ of work, with no differences between groups (p=0.65). LC caused greater soreness than SHC (p<0.01). LC resulted in prolonged strength loss that recovered 4 days post‐exercise (p<0.01). SHC caused immediate but not prolonged strength loss. SC per muscle fiber increased following LC (0.106 ± 0.031 and 0.126 ± 0.048 pre‐ and post‐exercise, respectively; p=0.028), while SHC caused no change in SC number (0.095 ± 0.025 and 0.101 ± 0.032 pre‐ and post‐exercise, respectively). There was no fiber type‐specific SC response. Conclusion We confirm SC activation following LC and show that a single bout of non‐damaging SHC does not stimulate SC activity.