Loss of muscle mass and strength are seemingly accepted as part of ageing process, despite ultimately leading to loss of independence. Maintaining a physically active lifestyle is regarded as the primary defence against loss of muscle function in older age. The present thesis aimed to examine the role of physical activity and exercise in maintaining leg muscle function in older adults. Associations between habitual physical activity and leg muscle function were explored in a cross sectional study of healthy older adults. Physical activity per se was not associated with leg muscle strength and power, in either absolute terms or relative to muscle size. Thereafter, in a randomised control trial, a homebased exercise strategy employing twice daily short bouts of unloaded exercise was identified as capable of producing measurable increases in leg muscle function in a one minute sit-to-stand test. Trends for increased thigh muscle cross sectional area and leg pressing strength and power, were also recorded. In a second randomised control trial, that ‘exercise snacking’ model was explored as means to prevent the anticipate loss of leg muscle mass and function in healthy older adults undertaking two weeks of reduced physical activity by way of step-reduction to <1,500 steps/day. Contrary to some previous literature, the step-reduction intervention induced losses of leg muscle function, however undertaking concomitant exercise snacking was demonstrated to be a promising countermeasure against reduced activity induced loss of dynamic leg strength and power. In summary, exercise snacking may be sufficient to increase leg muscle size and function in healthy older adults, and provide a feasible means to prevent loss of muscle function during periods of reduced activity.