Aims: To investigate the effects of a brief isometric exercise intervention, delivered online, on smoking urges, affect, and the number of cigarettes smoked per day. Method: Forty-nine participants smoking five or more cigarettes per day were recruited to an online study and randomised to an isometric exercise (IE) or relaxation (body-scan) intervention, which they were asked to use in response to smoking urges over the next 24 hours. Smoking behaviour, smoking urges, mood, affect, and interest and confidence in quitting smoking were assessed pre and post-intervention. Results: No significant differences were found between IE and relaxation with regards to negative affect or the number of cigarettes smoked in the 24 hours following the intervention, but the reductions in both were highly significant over time. The urge to smoke significantly decreased immediately post-intervention. Conclusions: Brief IE and relaxation interventions delivered online are equally effective in reducing smoking urges, negative affect, and the number of cigarettes smoked in the 24-hours post-intervention. The mechanisms underlying the effectiveness of these body-focused strategies remain unclear and should be explored in future research.