Relative and absolute intensity accelerometer metrics decipher the effects of age, sex, and occupation on physical activity.

BACKGROUND

To investigate whether quantifying both the absolute and relative intensity of physical activity (PA) improves understanding of age, sex, and occupation-related differences in PA in healthy adults aged 20-89.

METHODS

In the cross-sectional COmPLETE study, participants (N = 460, 48% women, age 55 [IQR 37, 71]) wore accelerometers for up to 14 days and underwent cardiopulmonary exercise testing. Average acceleration (AvAcc) and distribution of intensity (IG) of PA across the day were expressed in absolute terms () and relative () to the acceleration at the individual´s maximum intensity, predicted from cardiorespiratory fitness.

RESULTS

After initial increases, AvAcc_ and IG_ continuously declined beyond age 40-45, whereas AvAcc_ and IG_ increased until stabilising at age ~ 70 and declining at age ~ 60, respectively. Cardiorespiratory fitness constantly declined. Women had trivially higher AvAcc_ and moderately higher AvAcc_, but not IG_ and IG, than men. Occupations involving at least moderate PA showed higher AvAcc_ and AvAcc_, but not IG_ and IG indicating longer periods of low-intensity PA, compared to sitting/standing occupations.

CONCLUSIONS

Distinct age trajectories of absolute and relative metrics as well as cardiorespiratory fitness suggest that the age-related decline in the latter preceded that of PA. Women's higher AvAcc_ and AvAcc_ relate to more low-intensity PA combined with lower cardiorespiratory fitness rather than more health-enhancing higher-intensity PA. Finally, the intensity profile of occupational PA may provide insight into why occupational PA appears to lack a prophylactic association with health. Quantifying both the absolute and relative intensity of accelerometer-assessed PA provides greater insight than either alone.

TRIAL REGISTRATION

On clinicaltrials.gov (NCT03986892). Retrospectively registered 14 June 2019.