Muscle strength and physical education: epidemiological studies of factors in adolescence and their association with later morbidity

Although Physical Education (PE) is a part of the school curriculum in many countries, the association between the performance in PE and later morbidity is largely unknown. An important marker of health, cardiorespiratory fitness is inversely associated with future cardiovascular disease (CVD) and mortality. It has been suggested that muscle strength is associated in a similar way. However, whether low muscle strength in youth is a risk factor for CVD independently of cardiorespiratory fitness is not known. In a cohort of men and women, I investigated the association between PE performance in adolescence and morbidity in middle age (paper I and II). In cohorts of adolescent men, I investigated isometric muscle strength as a risk factor for later musculoskeletal pain (paper III), CVD, and mortality (paper IV). In women, low PE performance was associated with having a musculoskeletal diagnosis as well as with increased sick leave and increased number of physician visits. Men with low muscle strength did not have an increased risk for musculoskeletal pain but an increased risk of ischemic CVD as well as middle age CVD mortality. Notably, the associations were independent of cardiorespiratory fitness. In summary, I conclude the following 1) Adolescent girls with low PE performance could be important to target with early interventions to reduce future musculoskeletal illness and health impairment. 2) General isometric muscle strength in youth is not a risk factor for adult musculoskeletal pain in men. 3) The role of muscle strength in the development of CVD warrants further attention.