Physical activity at age 11 years and chronic disabling fatigue at ages 13 and 16 years in a UK birth cohort

OBJECTIVE: To investigate associations of physical activity at age 11 years with chronic disabling fatigue (CDF) at ages 13 and 16 years. DESIGN: Longitudinal birth cohort. SETTING: South-West England. PARTICIPANTS: Adolescents enrolled in the Avon Longitudinal Study of Parents and Children. OUTCOMES AND EXPOSURES: We identified adolescents who had disabling fatigue of >6 months' duration without a known cause at ages 13 and 16 years. Total and moderate-to-vigorous physical activity and sedentary time at age 11 years were measured by accelerometry over a 7-day period. RESULTS: A total physical activity level 100 counts/min higher at age 11 years was associated with 25% lower odds of CDF at age 13 years (OR=0.75 (95% CI 0.59 to 0.95)), a 1% increase in the proportion of monitored time spent in moderate-to-vigorous activity was associated with 16% lower odds of CDF (OR=0.84 (95% CI 0.69 to 1.01)) and a 1-hour increase in sedentary time was associated with 35% higher odds of CDF (OR=1.35 (95% CI 1.02 to 1.79)). Disabling fatigue of only 3–5 months’ duration at age 13 years had weaker associations with physical activity, and CDF at age 16 years was not associated with physical activity at age 11 years. CONCLUSIONS: Children who had chronic disabling fatigue at age 13 years had lower levels of total and moderate-to-vigorous physical activity and more sedentary time 2 years previously, but this association could be explained by reverse causation.