# Joint effect of physical capacity and physical activity predicts depression progression in middle-aged and older Chinese adults

## TL;DR

This study shows that physical capacity and activity together influence depression in older Chinese adults, with sex-specific differences in how these factors affect mental health over time.

## Contribution

The study introduces a quadrant-based approach to examine the joint effect of physical capacity and activity on depression progression in older adults.

## Key findings

- Participants in the 'can do, do do' and 'can do, don't do' quadrants had lower depressive symptoms at baseline compared to the 'can’t do, don’t do' group.
- Women with preserved physical capacity showed a steeper increase in depressive symptoms over time despite lower initial levels.
- Longitudinal changes in depressive symptoms varied by sex, with men showing similar patterns across quadrants.

## Abstract

Physical capacity (PC) and physical activity (PA) are key behavioural and physiological determinants of mental health, yet their joint effect on the progression of depression remains unclear. Understanding how these domains interact within a biobehavioural framework may help identify modifiable factors to prevent depression in ageing populations. Using a quadrant-based biobehavioural approach, we aimed to examine the joint effect of PC and PA on the progression of depressive symptoms.

We drew data for a cohort of participants surveyed in the China Health and Retirement Longitudinal Study from 2011 to 2018. PC was assessed by the Short Physical Performance Battery, and PA by weekly metabolic equivalent of task minutes. Participants were categorised into four PC-PA quadrants: ‘can do, do do’, ‘can do, don’t do’, ‘can’t do, do do’, and ‘can’t do, don’t do’. Depressive symptoms were measured repeatedly with the 10-item Center for Epidemiologic Studies Depression Scale. We used linear mixed-effects models to estimate trajectories of depression across quadrants.

Compared with the ‘can’t do, don’t do’ group, participants in the ‘can do, do do’ (P = 0.001) and ‘can do, don’t do’ (P < 0.001) quadrants had significantly lower depressive symptom levels at baseline. Longitudinal trajectories of depressive symptoms differed by sex: changes over time were largely similar across PC-PA quadrants among men, while women with preserved PC showed a steeper increase in depressive symptoms over time despite lower baseline levels.

Preserved PC is associated with a more favourable mental health status in middle-aged and older adults, including those with low PA. Sex-specific differences in longitudinal depressive symptom patterns highlight the need to consider PC when monitoring mental health in ageing populations.