Morning endurance training induces superior performance adaptations compared with afternoon training in mice

This study demonstrates that endurance training in the early-active phase induces greater performance adaptations than late-active phase training in mice, resulting in overcoming diurnal differences in exercise performance, despite lower absolute training volumes. These findings reveal exercise timing influences training efficiency, likely via circadian regulation of skeletal muscle metabolism. This work identifies time-of-day as a biologically relevant and underappreciated variable contributing to the heterogeneity of exercise responses, even in tightly controlled preclinical models.