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 and sedentary behavior 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 4 days and answered a question on perceived fitness. First, individual differences were studied between four fitness categories. Second, pairwise differences were examined among twin pairs discordant for fitness. Results: Self-reported fitness explained moderately the variation in objectively measured physical activity parameters: R-2 for daily steps 26%, for daily mean metabolic equivalent 31%, for daily moderate-to-vigorous activity time 31%, and lower for sedentary behavior time 14% (all p < .001). Better self-reported fitness was associated with more steps taken on average (8,558 daily steps [very good fitness] vs 2,797 steps [poor fitness], p < .001) and with a higher amount of moderate-to-vigorous activity (61 min vs 12 min p < .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 moderate-to-vigorous activity, and had less sedentary behavior (all, p < .05) compared to their less fit co-twins; however, difference was smaller among monozygotic than dizygotic 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.