Notch signaling expression in regenerating muscle following injurious downhill running (DHR) was characterized in male C57BL/J6 mice (3 mo). Hindlimb muscles were harvested from control mice or at 24, 48, 72, 96 or 120 h post-DHR. Muscle injury was observed at 96 h (3.3-fold) and 120 h (3.7-fold) post-DHR (P < 0.01) and elevated MCadherin expression at 72 h (2.7-fold), 96 h (2.4-fold) post-DHR (P < 0.05) and 120 h (3.3-fold) post-DHR (P < 0.01). Desmin increased at 72 h (2.2-fold), 96 h (3-fold) and 120 h (1.8-fold) post-DHR (P < 0.05). Delta1 +/MCadherin + cells increased approximately 2-fold at 72, 96 (P < 0.01) and 120 h post-DHR (P < 0.05). Isolated muscle-associated cells increased Delta1 (2.6-fold) (P < 0.05) and Notch1 (fourfold) (P < 0.01) expression at 120 h post-DHR. The results of this novel study indicate that DHR up-regulates Notch components within myoblasts and regenerating muscle.