Exercice Physique et Squelette

Abstract

The skeleton provides more than only a framework for the body. Bone is a calcified conjunctive tissue sensitive to various mechanical stimuli, mainly to those resulting from gravity and muscular contractions. Numerous animal and human studies demonstrate the importance of weight-bearing physical activity as well as mechanical loading for maintaining skeletal integrity. Lack of weight-bearing activity is dangerous for the skeleton: a decrease in bone mineral density (BMD) has been demonstrated in animals and humans under conditions of weightlessness or immobilization. Other studies have also reported a lower vertebral BMD among young amenorrheic athletes than among athletes with regular cycles and/or non athletes. The main factor responsible for this lower BMD in the amenorrheic athletes is the persistent low level of endogenous estrogen observed among these women. However this does not represent a premature and irreversible loss of bone mass since the resumption of menses following a decrease in training is the primary factor for a significant increase in vertebral BMD in these formerly amenorrheic athletes. A weight-bearing exercise is likely to be more beneficial at weight-bearing than at non weight-bearing sites, and hypogonadism resulting from very intensive training and exercise is more detrimental to trabecular than cortical bone. Bone deficit at non weight-bearing sites may be attenuated by maintenance of body weight. Nevertheless the etiology of "stress fractures" among athletes remains poorly understood, and the exact relationship between soft tissue mass and BMD is not clear. Osteoporosis, the most common bone disorder in France, is a pathological condition associated with increased loss of bone mass, resulting in a greater risk of fracture. Although symptoms of osteoporosis do not generally occur until after menopause, recent evidence suggests that bone loss starts much earlier in life. Therefore osteoporosis might be prevented by increasing peak bone mass and/or by slowering bone loss after menopause. Exercise such as resistance training or weight-bearing activities like running or walking have an osteogenic effect on increasing BMD in young people, and the decrease in BMD is slower in exercised than in non-exercised post-menopausal women. Nevertheless the influence of the length and of the intensity of such physical activities remain to be determined.

Influence of clenbuterol on bone metabolism in exercised or sedentary rats

“…Mechanical loading plays a major role in the development and maintenance of bone mass. Clinical and experimental studies demonstrate that moderate and repeated physical activity is able to increase bone mass in both animals and humans (1). Mechanical loading influences bone mass through the strains it engenders into bone tissue either as a result from the strain itself or due to changes in the streaming potentials, intralacunar pressure, and fluid flow, or through deformations in the extracellular matrix (17).…”

Treadmill running starting 3 months after orchidectomy restores femoral bone mass in rats

“…Nevertheless, numerous investigations have demonstrated a positive association between moderate physical activity and bone mass in humans (Barlet et al 1995). Similarly, endurance running (Saville and White 1969;Shimegi et al 1990;Forwood and Parker 1991;Yeh et al 1993), wheel running (Leblance et al 1983Newhall et al 1991;Umemura et al 1992) and jump training (Umemura et al 1995) has been shown to increase bone mass in rats.…”

“…We have previously demonstrated that treadmill running starting immediately after orchidectomy prevents bone loss in young rats, mainly by inhibiting bone resorption, as indicated by decreased urinary deoxypyridinoline (DPD) excretion (Horcajada et al 1997). It has also been demonstrated that moderate physical exercise is eective in preventing human involutional bone loss and osteoporosis (Barlet et al 1995). However it is dicult to conduct life-time studies in humans.…”

Electromyographic Activity of the Lower Limb Muscles during <i>Salat</i> and Specific Exercises

“…Regular exercise is quite an effective tool in the prevention and rehabilitation of cardiovascular diseases 13) . Barlet et al found that a regular program of weight-bearing exercise, such as walking can increase bone health and strength even among individuals with osteoporosis 14) .…”