Self- reported fitness and objectively measured physical activity profile among older adults: a twin study.

BACKGROUND: Maintaining good fitness and good level of physical activity are important factors for maintaining physical independence later in life. The aim was to investigate the relationship between self-reported fitness and objectively measured physical activity (PA) and sedentary behavior (SB) in the elderly.

METHODS: Same-sex twin pairs born 1940-1944 in Finland were invited to the study. Altogether 787 individuals (mean age 72.9 years), of whom 404 were female, used a hip-worn triaxial accelerometer for at least four days and answered a question on perceived fitness. First, individual differences were studied between four fitness categories. Secondly, pairwise differences were examined among twin pairs discordant for fitness.

RESULTS: Self-reported fitness explained moderately the variation in objectively measured PA parameters: R2 for daily steps 26%, for daily mean MET 31%, for daily moderate-to-vigorous activity (MVPA) time 31%, and lower for SB time 14 % (all p<0.001). Better self-reported fitness was associated with more steps taken on average (8558 daily steps (very good fitness) vs. 2797 steps (poor fitness), p<0.001) and with a higher amount of MVPA (61 min vs. 12 min p<0.001, respectively) in the adjusted multivariable model. Among 156 twin pairs discordant for self-reported fitness, co-twins with better fitness took more steps, did more MVPA and had less SB (all, p<0.05) compared to their less fit co-twins, however difference was smaller among MZ than DZ pairs.

CONCLUSION: One simple question on self-reported fitness is associated with daily activity profile among community-dwelling older people. However, genetic factors modulate this association to some extent.