The effects of tmkhg, immobilization and remobilization on musculoskeletal tissue. 1. ?f.aining and immobilization. Scand J Med Sci Sports W 2 10048.The effects of Merent types of training and immobilization on muscle tissue have been studied intensively and have been well established. At the beginning of strength or power train@, the increase in muscular performance can be explained by neural and psychological adaptation; that is, recruitment of more motor units per time unit, learning of more effective and economical usage of the active motor units and reduction of the inhiiitoIy inputs to the active alpha motor neurons. A€ter 6 to 8 weeks, further progress is due to gradual muscular hypertrophy; that is, a true increase in size of pre-existing fibres. =y, the theoxy of muscular hyperplasia (new fibre formation by a splitting of existing fibres) is not supported in uitid reviews. With endurance training there is an increased concentration and volume density of muscle mitochondria with correspond& biochemical adaptation, allowing the muscle to produce more mechanical power output aerobically and to be activated for longer periods of time without being fatigued. Immobilization, in turn, atrophies the muscle veq quickly, signiticantly already after one week. The most striking morphological findings are reduction in fibre size and diameter, reduction in the capillary density and a simultaneous increase in intramconnective tissue. At the same time, many harmful functional and biochemical effects also occur. Compared with muscle tissue, the knowledge of the effects of training and immobilization on tendon or ligament tissue is scarce and research has not been systematic.In animal experiments the tenaile strength, elastic stitbess and total weight of a tendon or ligament have increased due to training (collagen fibre thickening) and decreased due to immobilization (fibre splittiug and disorientation). These changes can be explained by an exercise (immobktion)-in-' duced increase (decrease) in synthesis of collagen and protmglycan-water matrix due to increased (decreased) fibroblast activity. The effects of training on the mptendinous junction or proprioceptom (muscle spmdles and Go@ tendon organs) are largely unknown. Our recent studies s h d that immobili-I zation is very detrkntal to these organs morphologicauy as well as biochemicthe articular cartilage: the cells and nuclei of chondrocytes enlarge and the proteoglycan content and cartilage thickurn increase. However, if training is too strenuous or biornechanically misloading, a degeneration process of the cartilage may begin, which is also the case in an immobilized joint. Bone tissue adapts to weight-krhg and muscular work well by increasing bone mass and density, most probably through osteoblast stimulation. The remodelling cycle of bone tissue is, however, a slow process, taking at least several months to OCCUT. The achieved bone mass is also dependent on genetic, nutritional and hormonal factors. Immobilization, on the other hand, causes exactly the reverse e...