Objectives: To assess the association between physical activity and subsequent physical functioning in middle-aged adults across a range of body mass index (BMI) categories.
Design: Prospective nationally representative cohort studies.
Setting: The United States and England.
Participants: Eight thousand seven hundred two individuals in the United States and 1,507 in England aged 50 to 69 and free of impairment at baseline, followed up for 6 years.
Measurements: Self-reported and measured BMI and self-reported level of physical activity. Outcome measures were score on a physical performance battery and self-reported mobility impairment.
Results: In both studies, being overweight and being obese were associated with greater risk of impairment (than being of recommended weight). In all weight categories and both countries, higher levels of physical activity were associated with lower risks of mobility impairment. For example, U.S. respondents of recommended weight (BMI 20-25) who were active on 3 or more days per week had a relative risk (RR) of incident mobility difficulties, compared with those who were less active, of 0.56 (95% confidence interval (CI)=0.40-0.78); for those who were obese (BMI >/=30) the corresponding RR was 0.59 (95% CI=0.45-0.76).
Conclusion: Excess bodyweight is a risk factor for impaired physical function in middle-aged and older people. Physical activity is protective of impaired physical functioning in this age group in subjects with recommended weight, overweight, and obesity. Older adults should be encouraged to engage in appropriate levels of physical activity irrespective of their weight.