Adaptability of older people to exercise Crosssectional perspective

In Fig. 3.3.3 the decline in sports performance that occurs with increasing age was described in terms of changes in world record performances. These athletes represent a highly elite population of individuals, some of whom have continued in competition since adulthood, whilst others are those who have come into a sport as a master or veteran competitor. Physiologic analysis in the laboratory of these athletes reveals that as a general rule, and as with their performance or competition data, there is a decline in a number of laboratory-based physiologic parameters. Nevertheless, it must be remembered that, although in decline, in absolute terms these individuals are considerably superior when compared with their non-active age-matched counterparts.

Strength and power

In an important study, Klitgaard et al. [44] investigated muscle function and composition in four groups of men aged 69 years, who had undertaken different types of physical training (swimming, endurance running, weight-lifting) over the previous 6 years and compared them with non-active men of a similar age and a group of young men who were also non-trained. They reported that among the older subjects the size and strength of the knee extensor muscles was greatest in those older men who had been strength training and that their strength values were actually similar to those of the non-trained young men (Fig. 3.3.6). In a similar study Sipila et al. [45] studied 82 Finnish master athletes and confirmed that this (as well as other major muscle groups) group was stronger in weight lifters when compared with non-trained and endurance-trained individuals. In addition, Harridge et al. [46] reported that although having a high level of aerobic power (35.6-46.8 mL/kg/min in those aged 70-76 years), lifelong orienteering athletes of up to 95 years of age were no stronger than those of non-active individuals. These data suggest that for the maintenance of muscle strength, exercise which involves high muscle forces is of critical importance.

The explanation for the superior muscle function described for strength and power athletes appears to lie in a larger muscle mass, relatively greater type II muscle fiber area [44] and an apparent maintenance of sarcoplasmic reticulum function [47].

Aerobic power

As with muscle strength and power, it is clear that master athletes have Vo2max values considerably higher than those of non-active individuals. Saltin [48] reported that inactive and still active elite orienteers differed in their Vo values, but not the rates of

decline (about 10% per decade). Endurance training however, does not appear to affect the decline in maximum heart rate. Cardiac output is better maintained in these individuals through increased stroke volume and they appear to retain a greater peripheral vasodila-tory response. At the level of skeletal muscle it is unclear as to whether there is an age-related effect on the ability of muscle to utilize O2. This uncertainty arises because in old as well as young subjects muscle capillary density and oxidative enzyme levels are highly sensitive to activity levels. Indeed, in a study by Coggan et al. [49], which compared master athletes

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Fig. 3.3.6 Muscle strength (a), size (b), torque per unit area (c) and the size of type II muscle fibers (d) in different populations of older men aged 70 years (strength trained, running endurance trained, non-active) and a group of non-active young men. (Data from [47].) These cross-sectional data highlight the likely effects of different training regimens on muscle size and strength and emphasize the need for resistancetype exercise for maintaining muscle mass and strength. For clarity endurance swimmers are not shown.

Fig. 3.3.6 Muscle strength (a), size (b), torque per unit area (c) and the size of type II muscle fibers (d) in different populations of older men aged 70 years (strength trained, running endurance trained, non-active) and a group of non-active young men. (Data from [47].) These cross-sectional data highlight the likely effects of different training regimens on muscle size and strength and emphasize the need for resistancetype exercise for maintaining muscle mass and strength. For clarity endurance swimmers are not shown.

with young runners matched for amount and absolute training intensity, the muscle biopsies from the older athletes were found to have higher oxidative enzyme activities and capillary/fiber ratios than their younger counterparts.

Bone

It is well known that if bones are not subjected to mechanical load, as happens with extreme forms of physical inactivity, reduced mass and strength are readily observed. Prolonged bed rest and limb immobilization may result in an average bone loss of 1-2% per week in trabecular bone sites such as the calcaneus [50]. Reversal of the bone loss is poor, though substantial individual differences may be observed.

The evidence in human studies supporting an association between increased physical exercise and bone mass first came from studies of athletes. The top curve outlined in Fig. 3.3.5 is warranted by the results of numerous cross-sectional and some longitudinal observational studies which show that athletes from various sports, especially from strength and power events, achieve and preserve superior bone mass compared to their non-athletic counterparts. In elderly males, the differences in BMD in the loaded bone sites and in the dominant/non-dominant bone comparisons in unilateral sports have been in the order of 10-20% [51]. Studies in elderly female athletes have, however, been fewer and shown less pronounced differences, probably because of their less intensive exercise habits and the greater role of body weight and fat mass as determinants of BMD.

Connective tissue

As with bones, immobilization deteriorates the soft connective tissue structures thus precipitating the reduction of their mechanical competence with aging. In skeletal muscle, immobilization in a shortened position results in a loss of serial sarcomeres and an increase in the proportion of collagen, less extensible collagen fibers, and an increased stiffness [52]. Such an immobilization is also accompanied by decreased collagen biosynthesis in muscle and tendon [33].

One of the first cross-sectional studies to suggest a responsiveness of human muscle collagen to physical training was reported by Suominen and Heikkinen [53] who found an increased prolyl 4-hydroxylase ac tivity (PH) in the vastus lateralis in middle-aged and elderly male endurance-trained athletes when compared to sedentary controls. The trained and untrained men also showed differences in 'non-loaded' connective tissue, the athletes having higher values in skin thickness, stiffness and elastic efficiency [54]. In subsequent studies, older endurance and power athletes were suggested to have maintained better muscle architecture with firmer fasciae and connective tissue septa and wider Achilles tendons than men in a population sample when assessed by ultrasonography [55,56].

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