Changes in muscle stiffness caused by reduced joint mobility

Effects of immobilization and subsequent low- and high-intensity exercise on morphology of rat calf muscles

After a cast immobilization of 3 weeks, the effects of 4-week remobilization by free cage activity or treadmill running on the morphology of the rat soleus and gastrocnemius muscles were studied. The studied morphometric parameters were: percentage volume of intramuscular connective tissue, capillary density, muscle fiber size, number of fibers with a pathological structural alteration, and fiber type distribution. In both muscles, immobilization of 3 weeks produced a significant increase in the connective tissue volume and number of fibers with pathological alterations, with a similar decrease in the capillary number and fiber size. At the same time, the relative amount of type I fibers decreased and type IIA fibers increased. Free remobilization and especially intensified remobilization by treadmill running significantly restored these values towards controls. These findings indicate that in rat soleus and gastrocnemius muscles immobilization-induced accumulation of intramuscular connective tissue, capillary loss, reduction in fiber size, accumulation of fibers with pathological structural alterations, and changes in fiber type distribution are to a great extent reversible phenomena, especially if remobilization is intensified by physical training. In clinical practice, this suggests that in patients with musculoskeletal injuries the postimmobilization rehabilitation should be early and effective.

Joint mobility and the oscillation characteristics of muscle

The aim of this study was to investigate which muscle characteristics of oscillation of the lower extremities have influence on trunk forward flexion and knee extension. The frequency and the decrement of damped oscillation of the muscles m. rectus femoris, m. biceps femoris, m. semitendinosus and t. semimembranosus in relaxed, contracted or stretched states were recorded by the myometer among the 22 first-year male students of the department of physical education. The subjects were divided twice into two groups according to: 1) the values of the trunk forward flexion, and 2) the values of the knee extension range of motion. The oscillation frequency of m. rectus femoris of the groups with high trunk forward flexion and high knee extension range of motion was lower than in groups with less range of motion. The similarity was followed in the decrement of m. semitendinosus. The difference between the decrements of the relaxed and stretched state of m. semitendinosus and the decrement of the relaxed state of the same muscle tendon correlated with the knee extension range of motion (r=0.46 and r=0.48, P<0.05). The relationship between the decrement of the relaxed state of m. biceps femons and the range of motion was r=-0.51 (P<0.01). The results of this study showed that the characteristics of the damped oscillation as indirect parameters of viscoelastic properties of the muscles were related to the joint mobility.