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Theories regarding how exercise can become addictive, and studies of withdrawal from exercise are reviewed. Several physiological mechanisms, including endogenous opioids, catecholamines, and dopamine pathways, have been implicated in exerdse dependence. The higher levels of endogenous opioids found following strenuous exercise, has prompted researchers to suggest that a form of auto-addiction to these hormones might be responsible for continued excessive exercising in humans. As well, investigators have suggested that, exerdse dependence could be the result of a dependence on the exercise stimulated release of catecholamines, resulting in an over-arousal of the sympathetic nervous system. Moreover, the increased stimulation of dopaminergic brain structures by exercise, and the likely involvement of these structures in behavioural and pharmacological addictions, could provide another explanation for exercise-dependent behaviour. Finally, reports of withdrawal symptoms following cessation of regular exercise, has led investigators to propose that exercise can, like pharmacological and other behavioural stimuli, become addictive.

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he reasons why older women exercise were investigated in a sample of 218 participants (mean age = T 67.5 years). The women, recruited from communityorganised exercise programs, completed a 25-item version of the Participation Motivation Questionnaire adapted for use with older Australians. The reasons for exercising rated as most important by the sample related to maintaining or improving fitness and enjoying the activity and liking the company. The motives that were reported as least influential related to wanting to be noticed, to be popular, and to feel important. Analysis of the data revealed five factors. When the sample was categorised into young-old (50-64 years, n = 84), mid-old (65-74 years, n = 89), and old-old (75+ years, n = 45), discriminant function analysis showed that the oldest women placed significantly more importance on sociaVactivity motives and less on personal fulfilment motives than did the younger groups. The present findings have potential value in designing strategies to encourage older Australian women to exercise.

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