Physical rehabilitation in the form of voluntary wheel running causes the development of a fibrotic scar in the defect area of the injured muscle. Whole TA muscle cross-sections of the injured muscle of the SED (A) and RUN (B) groups are presented. White dashed line illustrates the formation fibrotic scar in the injured muscle of the RUN group (B). White dashed boxes indicate the approximate region where images were taken in the defect area of the SED (C) and RUN (D) groups. No muscle regeneration was observed in either group.