This study examined the effect of three test meals on exercise tolerance of an individual with McArdle's disease, a myopathy characterized by phosphorylase b deficiency. The subject's exercise tolerance and ability to achieve the second wind, in response to each test meal, was evaluated over a 16-week period using a bicycle ergometer in a double-blind situation. Data were analyzed using one-way analysis of variance. No significant differences were found. It was concluded that a high protein meal, a high polyunsaturated fat meal, and a meal containing MCT oil did not affect the exercise tolerance of this individual compared to the control meal.