The Effects of Aging and Training on Skeletal Muscle

Abstract

Aging results in a gradual loss of muscle function, and there are predictable age-related alterations in skeletal muscle function. The typical adult will lose muscle mass with age; the loss varies according to sex and the level of muscle activity. At the cellular level, muscles loose both cross-sectional area and fiber numbers, with type II muscle fibers being the most affected by aging. Some denervation of fibers may occur. The combination of these factors leads to an increased percentage of type 1 fibers in older adults. Metabolically, the glycolytic enzymes seem to be little affected by aging, but the aerobic enzymes appear to decline with age. Aged skeletal muscle produces less force and there is a general "slowing" of the mechanical characteristics of muscle. However, neither reduced muscle demand nor the subsequent loss of function is inevitable with aging. These losses can be minimized or even reversed with training. Endurance training can improve the aerobic capacity of muscle, and resistance training can improve central nervous system recruitment of muscle and increase muscle mass. Therefore, physical activity throughout life is encouraged to prevent much of the age-related impact on skeletal muscle.

Assessment of post-competition peak blood lactate in male and female master swimmers aged 40–79 years and its relationship with swimming performance

“…Since the glycolytic metabolism depends on muscle mass, especially on the proportion of fast-twitch fibres, muscles with the same area, but occupied by a relatively smaller area of fast-twitch fibres, will be able to generate less [La] b and lower La' . Ageing seems to affect minimally the efficiency of the glycolytic enzymes (Kirkendall and Garrett 1998); however, it has been previously shown that in young adults the maximal activity of glycolytic enzymes is higher in males than in females with the latter showing a reduced capacity for anaerobic glycolysis (Green et al 1984).…”

Control of support limb muscles in recovery after tripping in young and older subjects

“…Among the older subjects several falls occurred, which are likely due to a limitation in this recovery mechanism, as older fallers showed a slower generation of joint moments and a lower peak ankle moment in the support limb than older non-fallers (Pijnappels et al 2004c). Probably this is partly due to a deterioration in muscle contraction mechanisms with age (Thelen et al 1996), which can be the consequence of a range of factors such as loss of type II muscle fibers (Porter et al 1995;Tideiksaar 1997;Kirkendall and Garrett 1998) or tendon compliance (Reeves et al 2003). The present data, however, indicate that age-related reductions in the (rate of) muscle activation might contribute to the reduced (rate of) moment generation.…”

“…Similarly, elderly subjects were shown to be less able to recover after a sudden release from a leaning angle due to a slower development of mechanical responses (Thelen et al 1997). A loss of muscle fibers, predominantly of type II fibers, with ageing has been demonstrated (Porter et al 1995;Tideiksaar 1997;Kirkendall and Garrett 1998) and tendon compliance was shown to increase (Reeves et al 2003). These changes in muscle properties would cause muscles to become slower and less strong and thus might underlie the observed age effect on the recovery from tripping.…”

Age-related changes in physical functioning: correlates between objective and self-reported outcomes

“…Government statistics 45 have confirmed that adults ≥65 years have an increased life expectancy (8). Therefore, monitoring 46 physical function within healthy older populations is critical to facilitate the early identification of 47 minimise cardiovascular stress and avoid potential injury (31). The SF-36 is regarded as a generic 141 measure of health status (17).…”