FAMILIAL RESEMBLANCE FOR SEVEN YEAR CHANGES IN MUSCULOSKELETAL FITNESS

Cross-sectional family studies have indicated that variation in musculoskeletal fitness can be partially explained by genetic factors; however, the extent to which changes in musculoskeletal fitness over time are influenced by genes is not known. The purpose of this study was to determine the extent to which baseline and seven-year changes in musculoskeletal fitness aggregate within families. Data from the 1981 Canada Fitness Survey and the seven-year Campbell's Survey follow-up were used. The sample consisted of 1264 people (635 males, 629 females) between the ages of 7 and 69 years for whom measurements of musculoskeletal fitness were available at baseline. A sub-sample of 834 people had measurements at both baseline and follow-up. The sample was distributed among 502 nuclear families with an average size of 2.75. Sit-and-reach trunk flexibility (cm), number of push-ups without time limit, number of sit-ups in 60s, and hand grip strength (kg) were used as indicators of musculoskeletal fitness. The data were adjusted for the effects of age and BMI (and baseline phenotype for changes) using regression procedures, and were standardized to zero mean and unit variance within each of the four sex-by-generation groups (father, mothers, sons, daughters). The data were fit to a familial correlation model using the software SEGPATH. The results indicate significant familial resemblance for all indicators of musculoskeletal fitness for baseline measures and seven-year changes. Heritabilities were 64% for trunk flexibility, 46% for push-ups, 59% for sit-ups, and 48% for grip strength. Similarly, heritabilities for the change scores were 48% for trunk flexibility, 52% for push-ups, 41% for sit-ups, and 32% for grip strength. The results suggest that familial, and perhaps genetic, factors are important in explaining the variance in musculoskeletal fitness not only cross-sectionally, but also for changes over time. Segregation analyses using extended pedigrees and molecular genetic studies aimed at identifying specific genes that relate to musculoskeletal fitness are warranted. This research was supported by the Heart and Stroke Foundation of Canada.