A longitudinal study of physical activity and body mass index among persons with unexplained chronic fatigue.

Objective And Methods: A cohort of 100 patients with unexplained chronic fatigue (CF) was assessed longitudinally for 1.5 years to determine if physical activity (kcal expended), exercise capacity (VO(2)max), perceived exertion, and body mass index (BMI) changed over time and were associated with changes in CF-related clinical status.

Results: BMI increased significantly over time but did not predict changes in clinical status. Increasing energy expenditure was associated with increasing vitality and decreasing CF symptom severity over time, and decreasing perceived exertion was associated with increasing physical functioning. However, increasing perceived exertion was also associated with increasing CF symptoms.

Conclusions: These data do not support models that posit associations between CF and deconditioning.