Seven-year stability of physical activity and musculoskeletal fitness in the Canadian population

Background: Knowledge of population patterns of physical activity levels and musculoskeletal fitness are important in the selection of appropriate target groups for public health interventions. Purpose: To examine the stability of physical activity levels and musculoskeletal fitness in the Canadian population. Methods: The sample included 951 male and 958 female subjects, aged 11-69 yr, for whom the appropriate measurements were available in the 1981 Canada Fitness Survey and its 7-yr follow-up, the Campbell's Survey. Participants were divided into 2-yr age groups in childhood (11-18 yr) and 10-yr age groups in adulthood (19-69 yr). Measures of physical activity were estimated activity energy expenditure (AEE) and time spent on activity, whereas indicators of musculoskeletal fitness consisted of sit-ups, push-ups, grip strength, and sit-and-reach (trunk flexibility). Results: 7-yr inter-age correlations ranged from -0.08 to 0.39 for AEE, -0.10 to 0.33 for time on activity, 0.42 to 0.80 for sit-ups, -0.07 to 0.73 for push-ups, 0.44 to 0.82 for grip strength, and 0.47 to 0.85 for sit-and-reach. In general, significant tracking correlations for physical activity levels were limited to adulthood, whereas significant tracking of musculoskeletal fitness was observed at all ages for all indicators except push-ups. Male subjects exhibited greater stability in push-ups than female subjects. The average percentage of participants remaining in the lower and upper quintiles of the distribution over 7 yr was greater for musculoskeletal fitness (36-68%) than for physical activity level (30-34%). Conclusion: Physical activity level is not a very stable characteristic in the Canadian population; however, indicators of musculoskeletal fitness are moderately stable over 7 yr.