Physical exercise in the elderly: Its effects on the motor and endocrine system

Ageing is associated with reduced maximal aerobic power, muscle strength and power; namely, reduced fitness. Based on the existing evidence concerning exercise prescription for healthy adults, in 1990, the American College of Sports Medicine (ACSM) made the following recommendations: frequency of training: 3-5 days/-week, intensity: 60-90% HRmax, or 50-85%VO2max, duration: 20-60 min of continuous aerobic activity with involvement of large muscle groups. However, the target of improving/maintaining physical fitness is inappropriate for the whole elderly population, which includes the frail. In these subjects, the achievement of a better health status is certainly the primary goal, as recently stated by the 1996 Heidelberg guidelines. Physical activity should be prescribed on the basis of an individual health/fitness gradient with different goals. Lower levels of physical activity than those recommended by the ACSM may reduce the risk for certain chronic degenerative diseases and yet may not be of sufficient quantity or quality to improve VO2max. In the wake of these considerations and the inclusion of the improvement/maintaining of health status among the goals of exercise prescription in the elderly population, in 1991, the ACSM lowered the recommended exercise intensity to as low as 35-40%VO2max. One of the most critical consequences of ageing of the motor system is muscle weakness. Several causes may be held responsible for this phenomenon; among these sarcopenia is, probably, the most common. The latter involves both a decrease in muscle fibre size and number. However, atrophy cannot alone entirely account for senile muscle weakness. As a matter of fact, the maximum force that may be generated per muscle cross-sectional area (F/CSA) is lower in elderly subjects. This phenomenon suggests that muscular or neural factors, or more likely both, are involved. Another common cause for the decrease in F/CSA is muscle activation. Recent reports show incomplete quadriceps muscle activation in very old (80+) men and women. Since almost complete (95%) muscle activation was found in a population of subjects ∼70 year old, it seems that activation capacity rapidly falls beyond the 7th decade. Therefore, taken together, the above neural factors may account for large part of the decrease in force with ageing. Hormonal changes in themselves are not the simple explanation for all of the changes associated with ageing. Studying the effects of strength training on the endocrine system is complicated by a variety of factors related to both the exercise challenge itself and the accurate measurements of hormones. The measurement of hormonal changes is complicated by the manner in which they are released, transported and interact with the target tissue. Many hormones are released in a pulsatile manner with superimposed diurnal, monthly, and seasonal rhythms. They often exist in different molecular weight fractions and are frequently transported in a bound form. From the work that has been carried out in younger people it would appear, that if sufficient high resistance exercise is carried out, then the acute hormonal response is not qualitatively different to that following a bout of endurance exercise. Exercise training programs have been suggested as possible countermeasures against involutional bone loss, being able to prevent or reverse almost 1% of bone loss per year in both lumbar spine and femoral neck for both pre- and postmenopausal women. As far as elderly people are concerned, it appears that strength training may have a more beneficial effect than aerobic training on BMD, especially in postmenopausal women, although some evidence suggests that also aerobic training may improve BMD in the elderly. To date, the effect of physical activity on bone turnover has received limited attention despite the strict dependence of bone mass on the balance between bone formation and bone resorption. The equilibrium between these two components of bone turnover is crucial for bone mass and BMD, since bone loss, or increase, results from an uncoupling of bone formation and bone resorption. During the last few years there has been a rapid development of reliable methods to measure biochemical markers of bone metabolism. Since these markers reflect the cellular events, they may provide new opportunities to elucidate the effects of physical exercise on bone metabolism