Physical activity assessment and health outcomes in old age: how valid are dose–response relationships in epidemiologic studies?

In this systematic review the validity of the dose–response relationships between physical activity (PA) and energy expenditure (EE) on defined health outcomes (cardio- and cerebrovascular morbidity and mortality, cancer) for the elderly is questioned. Medline, Cochrane, and EMBASE databases were reviewed for epidemiological longitudinal studies in populations aged 60+ for the years 1985–2007. Although most of the 18 identified studies generally demonstrated an inverse dose–response relationship between PA and EE level with morbidity and mortality, the range of dose–responses was remarkably broad. The nature of the dose–response relationship remained unclear. PA questionnaires - even those constructed for the elderly - do not cover the extremely diverse aspects of age-specific PA behavior and modes of muscular activity. Only non-age-specific tables had been used to estimate the EE in the elderly. Direct measurements of EE were limited. The results have implications for the interpretation of the dose–response relationships between PA and EE on defined health outcomes in old age.