Validity of Self-Assessed Physical Fitness in Relation to Sex and Physical Activity Level

Abstract

In large-scale epidemiological studies, directly measured components of physical fitness is time-consuming and expensive. In a recent study, an instrument to selfassess aerobic fitness and muscle strength was shown to be valid and reliable among female health-care workers. However, the instrument has not been validated in other populations and it is unknown whether the physical activity level influences the ability to self-assess physical fitness. PURPOSE: To examine the validity of an instrument to self-assess physical fitness in male and female office workers (characterized by low physical work demands) and to evaluate if the self-assessment is influenced by sex and physical activity level. METHODS: The study population comprised 346 females and 190 males, age 23–67 years. Physical fitness components (muscle strength including back flexion and extension, shoulder elevation and abduction as well as aerobic fitness) were measured directly by performance-based tests and self-assessed by an illustrated scale ranging from 1 to 10. Physical activity level was assessed by questionnaire comparable to IPAQ (long version). Construct validity was evaluated by partial correlations between corresponding performance based and self-assessed components of physical fitness adjusted for sex and age by multiple linear regression analyses. Three groups were defined based on the level of physical activity (inactive/minimally active/sufficiently active) according to the IPAQ questionnaire and was tested in the model. So was the total amount of physical activity per week as well as the amount of vigorous physical activity per week RESULTS: Self-assessed aerobic fitness showed a satisfactory construct validity (r=0.47, p<0.0001) in both sexes, whereas self-assessed strength only showed a satisfactory construct validity for measured shoulder elevation strength in men (r=0.38, p<0.0001) and not in women (r=0.24, p<0.0001). The amount of vigorous physical activity, the total amount of physical activity and the activity group membership did not contribute to further explanation of the measured parameters. Further, the ability to self-assess was not dependent on the physical activity level in any of the three physical activity parameters. CONCLUSION: Self-assessment of aerobic fitness can also be used in office workers with low physical job demands and is not affected by sex. In contrast, self-assessed muscle strength showed a lower validity especially for women. The ability to selfassess physical fitness did not depend on the physical activity level.