Maintaining adequate levels of functional capacity and mobility are central to preserving an independent lifestyle and high quality of life, but deteriorating physical performance and diminished functional capacity are common features of ageing. The rate and scale of deterioration in the performance of particular activities, along with those factors which underlie it, are less well established.

A number of factors may limit physical performance including muscular strength, endurance, balance and coordination, whose relative importance will vary between activities. The investigations detailed in this thesis have examined the relationships between changes in muscle function with age, and the performance of activities to which the legs are central, particularly the vertical jump. The contribution of flexibility and balance to successful performance in young and elderly subjects has also been examined.

A clear age related decline was evidence in a number of activities, and most obvious in the vertical jump. In a group of 10 males aged 70.1 (SD3.95) years the mean vertical jump height attained was 0.12 (SD0.02)m, compared with 0.40(0.02)m in a group of 10 males aged 26.7 (SD2.3) years. A similar age related decline in performance was evident in females, and this was associated with a decrease in strength and power.

One striking observation was the considerable variation in performance between apparently similar individuals which, within an age group correlated only weakly with muscle strength and power. A poor correlation was found between performance in the vertical jump and power in young subjects, suggesting that other factors may change with age such as balance, flexibility and coordination. On examination however, the latter factors were found to be more variable in the elderly than in the young. Consequently the major change associated with the decline in performance with age is the loss of strength and especially power of the quadriceps, which was well correlated with jumping ability.

In females the age related decline in power was attributed to a loss of strength, but in males deteriorating muscle strength was accompanied by a reduction in maximal velocity of shortening.