Vascular density at the myotendinous junction of the rat gastrocnemius muscle after immobilization and remobilization.

Muscle injuries often occur at or near the myotendinous junction. Immobilization decreases the tensile strength of the myotendinous junction and predisposes it to strain injury. However, there are no data available on whether physical training or remobilization can lower the susceptibility of the myotendinous junction to strain injuries. We investigated the effects of three different remobilization programs (8 weeks) after immobilization (3 weeks) by evaluating the vascular density at the myotendinous junction of the rat gastrocnemius muscle. The myotendinous junctions had a portal system vascularity, or capillary-arteriole-capillary system, which probably protects the blood supply against pathologic conditions. The vascular density at the myotendinous junction decreased about 30% after immobilization (P < 0.001). After free cage remobilization for 8 weeks, the mean vascular density returned to the level of the controls. After progressively increasing running programs the vascular density was slightly higher in the immobilized myotendinous junction and about 50% higher than controls in the contralateral myotendinous junction (P < 0.001). The capacity of the vascular bed of the rat myotendinous junction to recover from immobilization atrophy seems to be good. Progressively increasing physical training improves the process of revascularization and probably protects an injured and immobilized muscle from reinjury.