Reciprocal Associations Between Trajectories of Physical Activity and Physical Function Among Older Women: Findings From the Australian Longitudinal Study on Women's Health.

Background: Although physical activity (PA) is known to improve physical function (PF), and functional decline impacts the capacity to engage in PA, the reciprocal relationship between PA and PF remains unclear.

Methods: Data were from participants in the 1921-1926 cohort of the Australian Longitudinal Study on Women's Health (N = 8 238). PA and PF were assessed at 3-year intervals from 1999 (73-78 y) to 2011 (85-90 y). Group-based trajectory modeling was used to identify PA and PF trajectories, and associations between PA and PF were examined using mixed-effects models and restricted cubic spline modeling.

Results: Three trajectories for PA and PF were identified: Low, Moderate, and High. Women in the High PA group maintained high PF and did not reach the starting PF level of the Low PA group (at age 73) until they were 87. Similarly, women in the High PF group maintained higher PA than those in the other groups. Women in the Low PF group never met PA guidelines and had PF scores below the disability threshold throughout the study. Restricted cubic splines showed that higher PA was associated with better PF 3 years later, and vice versa, indicating that PA and PF influence each other.

Conclusion: There are reciprocal relationships between PF and PA; higher levels of PA promote better PF, and higher PF may help slow the decline in PA. Although rates of decline in PF show little variation with PA in women during their 80s, habitually high PA confers considerable benefits, contributing to additional years of healthy life.