Beneficial effects of voluntary over forced exercise on skeletal muscle structure and myokines expression.

Background: Myokines, a group of small proteins - mainly cytokines, are released by myocytes during muscular contraction and proved to have many biological effects locally or at systemic levels. The main objective was to study the morphological alterations and myokines expression in rat gastrocnemius muscle following forced compared to voluntary muscle contraction. Materials and methods: Thirty-six adult male Wistar rats were divided into three groups: control, voluntary exercise and forced swimming regimen. The experiment last for 3 weeks. The weight of rats and serum corticosterone levels were recorded. The gastrocnemius muscle samples were processed for histological and immunohistochemical study of different myokines. Results: The mean weight of rats showed no statistical difference between groups. Corticosterone level significantly increased after forced exercise. Voluntary exercise muscle fibres appeared hypertrophied with prominent transverse banding and dominating satellite cells. Forced exercise muscle showed atrophied widely spaced muscle fibres and inflammatory cell infiltrate. Voluntary exercise significantly increased optic density of interleukin 6, macrophage inhibitory and brain derived neurotrophic factors, whereas the forced exercise group showed significant decrease in their optic densities. The optic density of vascular endothelial growth factor significantly decreased in the forced exercise group. Forced exercise could be harmful to the skeletal muscle fibres and it decreases the secretion of important myokines. Further, forced exercise significantly increases the serum corticosterone level. Conclusions: The use of exercise for the attainment of healthy life style or in psycho- or neuro-therapy should follow a thoroughly studied programme for welfare of human health.