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 age 13 and 16 years
Design: Longitudinal birth cohort
Setting: South west England
Participants: Adolescents enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC).
Outcomes and exposures: We identified adolescents who had disabling fatigue of >6 months' duration without a known cause at ages 13 and 16. Total and moderate-vigorous physical activity and sedentary time at age 11 were measured by accelerometry over a 7-day period.
Results: A total physical activity level 100 counts/minute higher at age 11 was associated with 25% lower odds of CDF at age 13 (odds ratio (OR) = 0.75 (95% CI 0.59, 0.95)), a 1% increase in the proportion of monitored time spent in moderate-vigorous activity was associated with 16% lower odds of CDF (OR = 0.84 (95% CI 0.69, 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, 1.79)). Disabling fatigue of only 3-5 months’ duration at age 13 had weaker associations with physical activity, and CDF at age 16 was not associated with physical activity at age 11.
Conclusions: Children who had chronic disabling fatigue at age 13 had lower levels of total and moderate-vigorous physical activity and more sedentary time two years previously, but this association could be explained by reverse causation.