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A single bout of exercise activates skeletal muscle satellite cells during subsequent overnight recovery

Skeletal muscle satellite cell (SC) content has been reported to increase following a single bout of exercise. Data on muscle fibre type‐specific SC content and/or SC activation status are presently lacking. The objective of the study was to determine the impact of a single bout of exercise on muscle fibre type‐specific SC content and activation status following subsequent overnight recovery. Eight healthy men (age, 20 ± 1 years) performed a single bout of combined endurance‐ and resistance‐type exercise. Muscle biopsies were collected before and immediately after exercise, and following 9 h of postexercise, overnight recovery. Muscle fibre type‐specific SC and myonuclear content and SC activation status were determined by immunohistochemical analyses. Satellite cell activation status was assessed by immunohistochemical staining for both Delta‐like homologue 1 (DLK1) and Ki‐67. Muscle fibre size and fibre area per nucleus were greater in type II compared with type I muscle fibres (P < 0.05). At baseline, no differences were observed in the percentage of SCs staining positive for DLK1 and/or Ki67 between fibre types. No significant changes were observed in SC content following 9 h of postexercise, overnight recovery; however, the percentage of DLK1‐positive SCs increased significantly during overnight recovery, from 22 ± 5 to 41 ± 5% and from 24 ± 6 to 51 ± 9% in the type I and II muscle fibres, respectively. No changes were observed in the percentage of Ki‐67‐positive SCs. A single bout of exercise activates both type I and II skeletal muscle fibre SCs within a single night of postexercise recovery, preceding the subsequent increase in SC content.