AGE-RELATED ALTERATIONS IN MUSCULAR ENDURANCE

Aging often results in a decline of most physiological systems of the body. However, the maintenance of some appropriate level of neuromuscu lar function into old age is critical if we expect the elderly to be a ble to maintain normal daily activity and functional independence. It is well established that muscular strength declines in old age, but an equally important parameter of neuromuscular function, muscular endur ance, has received only minimal attention in the literature. Important information regarding age-associated changes in muscular endurance ca n be obtained from both animal and human research models, each having their own set of limitations and advantages, One problem in trying to interpret past research dealing in this area is the fact that muscular endurance can be expressed in a variety of ways and can be measured b y a variety of techniques. It seems that conflicting reports arise fro m substantial differences in research design, statistical analyses or the ability to control extraneous influences such as physical activity levels and dietary intakes. This review will examine both human and a nimal literature in an attempt to elucidate methodological concerns in the assessment of muscular endurance and the controversial evidence r egarding changes in muscle morphology and muscle metabolism that may b e responsible for age-related changes in muscular endurance. Issues th at address the possible selective loss of fibre type and the declines in both total fibre number as well as fibre size will be presented, si nce muscle quantity and quality have obvious links to endurance capaci ty. In conjunction with the alterations reported in skeletal muscle ti ssue, muscle blood flow and the relationship between fibre and capilla ry numbers and their possible influences on substrate availability wil l also be discussed in relation to muscle endurance capabilities. Fina lly, the adaptive ability of aged skeletal muscle to improve muscular endurance by different training regimens and through different physiol ogical mechanisms will be investigated.