Effect of Physical Activity on the Lesion Repair Process in the Gastrocnemius Muscle of Rats

The present study aimed to evaluate the effect of a progressive load of physical activity on a musculoskeletal injury in rats. Sixty-four rates were divided into two groups: experimental group (EG), which underwent physical activity (swimming) with a progressive load, and the control group (CG), which was not submitted to this program. The training was carried out according to an adapted version of the Goncalves (1999) swimming system. Injuries were caused to the gastrocnemic muscle by inducing 40% NaOH. On days 2, 7, 14, and 21 after inducing muscle injury, the animals from both EC and CG were sacrificed. The injured area was removed and processed. The neutrophils, macrophages, lymphocytes, and plasmocytes were quantified by hematoxylin and eosin (HE GC=2.48±1.00; p=0.006) and lymphocytes (GE=2.12±0.82; GC=0.06±0.82; p=0.037) after 2 days, and of macrophages (GE=15.74±3.00; GC=6.02±1.95; p=0.007) and lymphocytes (GE=2.01±0.78; GC=0.14±0.09; p=0.044) after 7 days, could be observed in the EG when compared to the CG; however, the opposite was true for neutrophils (GE=48.12±17.04; GC=105.54±12.25; p=0.005). After 14 days, a smaller quantity of neutrophils (GE= 32.70±10.26; GC= 90.96±17.62; p= 0.044) and a larger quantity of plasmocytes (GE=9.06±3.84; GC=0.68±0.53; p=0.028) could be observed in the EG as compared to the CG. A greater area of type III collagen could be observed in the EG when compared to the CG over a 14-day period (GE=44.90±16.15; GC=0.74±0.40; p=0.000) and a 21-day period (GE=13.19±9.09; GC=1.02±0.94; p=0.029), whereas the opposite could be observed for type I collagen. The physical activity promoted an increase in the deposition of type III collagen in the muscle injury. This activity accelerated the repair process after 14 days, possibly moderated by the larger number of inflammatory cells, while after 21 days, the lesion presented a lesser resistance.