In the present study, we examined the utility of volitional and forced intentions in predicting participation in physical activities and effort within the theory of planned behaviour. Four hundred and forty-four participants (184 males, 260 females) aged 19.1 +/- 3.3 years (mean +/- s) completed self-report measures of intentions, attitudes, subjective norms, perceived behavioural control, volitional intentions, forced intentions, and past behaviour in a physical activity context. Six weeks later, they completed self-report measures of physical activity behaviour and effort. Results indicated that volitional intentions and forced intentions contributed to the prediction of effort over and above intentions, attitudes, subjective norms, perceptions of control, past behaviour, and the product terms of attitudesxintentions and subjective normsxintentions. Volitional intentions and forced intentions did not predict participation in physical activities over and above effort. We concluded that volitional intentions and forced intentions assist in the explanation of effort in the context of physical activity behaviour.