gms | German Medical Science

Physical activity and successful aging
10th International EGREPA Conference

European Group for Research into Elderly and Physical Activity

14.09. - 16.09.2006 in Köln

Skeletal muscle and aging

Meeting Abstract

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  • corresponding author J.A. Duarte - University of Porto, Portugal
  • H.J. Appell - German Sport University, Cologne

Physical activity and successful aging. Xth International EGREPA Conference. Cologne, 14.-16.09.2006. Düsseldorf, Köln: German Medical Science; 2006. Doc06pasa002

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Veröffentlicht: 18. Dezember 2006

© 2006 Duarte et al.
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Biological aging can consists of the progressive decline in body function with chronological age that predisposes individuals to the occurrence of diseases and to an increased risk of death. This eventual impairment of functionality is influenced by genetic and environmental factors and can be explained by a continuous loss of redundancy in organic systems, which results from the imbalance between the rate of cell death induced by physiological or pathological events and the rate of cellular repair. Depending on multiple genetic and environmental factors, the aging process shows a high interindividual variability. Beyond its overall effects on the entire organism, this process seems to affect various organs at different intensities. It is moreover assumed that aging of one organ or system may negatively influence the function of other organs thereby extrinsically accelerating their degeneration with age. Such interdependence becomes more apparent with the age in this sense of a vicious circle. Also diseases with local or systemic repercussions may enhance the rate of local and systemic degenerative processes thus contributing to an acceleration of the aging process. Such would favour the occurrence of additional cellular damage that in turns favours the incidence of organ failure. Therefore, any progress in the aging process is exponential and becomes apparent when the rate and efficiency of regenerative mechanisms are overwhelmed by the rate of cellular and tissue degeneration.

Considering skeletal muscle, the capacity to perform mechanical work is most affected with the enhancement of chronological age. Tissue oxidation and glycosilation are the intrinsic mechanisms classically associated with the severity of damage in skeletal muscle with age. Moreover, aging of skeletal muscle system may also accelerate the degenerative processes of other organs either by consequent disuse or by negative biomechanical effects. For instance, the interdependence of osteoarthritis and alterations of periarticular muscles is known and it is suggested that a weak quadriceps muscle cannot produce enough force to stabilize the knee and to prevent it from overload during the amortization of the mechanical impact during gait. Concerning the hip joint, recent data also support the concept that atrophy of abductor muscles should be of etiological importance for the development of contralateral hip osteoarthritis.

The function of skeletal muscle intimately depends on the central and peripheral nervous system, which controls muscle trophism and fibre type properties by regulating muscle gene expression. These neural effects on skeletal muscle involve two distinct mechanisms: a humoral mechanism mediated by the release of neural factors from the nerve terminals, and a neurophysiological mechanism mediated by the pattern of electrical nerve discharge. Interestingly, the degenerative morphological alterations observed in skeletal muscle with age strongly coincide with a chronic neuropathic process. The most evident change is a decrease in the total number of motor units. Loss of motor units not accompanied by an equal loss of muscle fibres suggests that each motor neuron innervates more muscle fibres in the aged than in younger muscles. These results are in accordance with the phenomenon of fibre type grouping and suggest an early preferential degeneration of the fast motor units with age. Considering all the above referred findings, it is suggested that skeletal muscle morphological and functional alterations with age do not only result from intrinsic factors within the muscle fibers but are mainly influenced by aging phenomena of the nervous system, especially of its peripheral components. In this sense, the alterations found in muscle fibres represent secondary effects based on the aging process of the nervous system. This concept should not only be useful to explain eventual losses in strength encountered at advanced ages, but should also explain the increased inability of elderly subjects to properly perform simple tasks of daily life. A loss of motor units and concomitantly larger motor units in general leads to an impaired coordination. Assuming that aged skeletal muscle has a reduced adaptive potential, due to a diminished number and reduced proliferative capacity of satellite cells, it can be assumed that the benefits of physical activity in the aged muscle, particularly observed after strength training, are mainly due to neural adaptations which might retard or prevent the consequences of the aging process primarily at the level of the nervous system, with beneficial secondary effects on the functional properties of skeletal muscle.