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.