Title: Exercise helps to preserve muscle function into old age
Key words: exercise, old age, geriatric, muscle function, sarcopenia, ageing, aging, inactivity, grip strength, cardiovascular function, aerobic capacity, fitness, function, muscle fibre, strength, mobility, endurance, oxidative capacity, aerobic training, resistance training, balance, repetitions, flexor, extensor, spine, pelvis, shoulder, walking, running, cycling,
Date: Oct 2006
Author: Morgan, G
Exercise helps to preserve muscle function into old age
Loss of muscle power and function, and increasing disability are concomitants of ageing. Increasing muscle disuse associated with ageing is the major precipitating factor. This review will look at the ability of rehabilitation programmes to stem or reverse this decline.
The increasing level of inactivity associated with ageing is apparent from surveys. One survey showed that 49% of women and 27% of men over the age of 70 in the US had substantial work or mobility limitations (Pinsky 1990). Another that in a 55-87 year old age group, 53% of those engaged in any form of sport discontinued it over a 3-year period (Visser 2002).
Grip strength correlates with general muscle power (Giampaoli 1999) and has been found to decrease with age, to the point where 28% of men and 66% of women over the age of 74 were unable to lift a weight greater than 4.5 Kg. (Jette 1981). Diminishing leg strength, correspondingly, leads to an increased incidence of falls (Baumgartner 1998, Day 2002), loss of balance and mobility (Wolfson 1995, Pinsky 2002). Increasing disability, in its train, leads to poorer cardiovascular function and increased morbidity (Pinsky 2002).
Loss of muscle power is associated with muscular wasting (Frontera 1991), which is progressive with age in the non-active (Tsankoff 1977). Muscular atrophy is directly related to a loss of muscle fibre numbers and muscle cross-sectional area (Lexell 1988). Loss of muscle is accompanied by reduction in muscular capillary density and aerobic capacity – both strength and fitness therefore diminish with age (Fleg 1988, Coggan 1992, McGuire 2001a). Even among lifelong master athletes some loss of function is inevitable: in this group aerobic capacity has been found to deteriorate by 5-10% per decade (Pollock 2002). This is wholly down to loss of muscle strength and its oxidative capacity and not to any fall off in cardiac output (Coggan 1992).
Against this background of progressive decline, there is now a large body of research showing a muscular adaptive response that can be maintained into advanced old age. The conclusion of this work is that strength; mobility and endurance capacity is most benefited by resistance type training. Such programmes bring about increases in muscle cross-sectional area, fat free mass, with increases in strength and endurance (Larrson 1982, Frontera 1988, Fiatarone 1994, Ades 1996). Peripheral oxidative capacity is improved through expansion of the muscular capillary network with an improvement in aerobic capacity (Frontera 1988, Coggan 1992, McGuire 2001b). Aerobic training is less effective – a minimum of 4 hours of walking a week has produced improvements in leg strength, mobility, and aerobic fitness and led to a reduction in cardiovascular disease (LaCroix 1996). Muscle mass remains unchanged, however, with this type of activity, with up to 12 months of relatively high intensity aerobic conditioning producing no additional benefit (Coggan 1992). All trials, whether strength or endurance based, have shown no great changes in fibre-type composition, in spite of ageing being characterised by a more selective loss of type II fibres (Frontera 1988, Coggan 1992).
Through its ability to increase muscle mass, resistance training has been shown to increase strength, mobility and balance and reduce the incidence of falls in the elderly (Campbell 1997, Baumgartner 1998, Day 2002). Comparison of different regimes confirms that, in this respect, higher intensities of training are more beneficial. Thus training to 80% of one maximal repetition (1RM) is more beneficial than training to 66% of this maximum (Moritani 1980, Frontera 1988). This conclusion has been embodied in the position stand of the American College of Sports Medicine (1990), which states that such training leads to maximum strength gains with greater levels of mobility and cardiovascular fitness.
From a practical viewpoint, supervised sessions in a group environment appear to produce the best results. Isotonic exercises that exercise the main flexor and extensor groups of the upper and lower extremities, with strengthening exercises for the shoulder, spine and pelvis, all 3 times a week, 3 sets of 8 repetitions at 80% of 1RM, have led to strength gains of 5% per session (Frontera 1988). These are remarkable results. Home programmes have been devised but tend to be less effective due to compliance problems (Campbell 1997). Walking is less beneficial but may be more acceptable for certain groups. This and other forms of aerobic activity are to be encouraged, both from mobility and a cardiovascular point of view. The critical role played by activity is illustrated by a group of middle aged subjects who were bed rested for 3 weeks and then were retested for cardiovascular fitness 30 years later - the loss in fitness over those 3 weeks was shown to be significantly greater than in the subsequent 30 years of low activity (McGuire 2001a). All forms of activity, but particularly structured resistance activities, are, therefore, likely to be beneficial for the aged.
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