The prevalence of obesity is high in older persons and recent trends show a rapid increase in this prevalence. Results from observational and intervention studies (i.e. weight loss studies) show the strong negative impact of obesity on functional status in old age. There are different potential pathways through which obesity may lead to functional decline in older persons. Furthermore, the presence of overweight and obesity during the life course and trends in medical care are likely to influence the impact of obesity on disability. The concepts sarcopenia (age-related loss of muscle mass) and dynapenia (age-related loss of muscle strength) receive a lot of research attention as potential determinants of functional decline in old age. There is no consensus on the definitions of these concepts. Recent studies conducted in large cohort studies of mainly community-dwelling older persons show that poor muscle strength is strongly associated with functional decline compared to low muscle mass. In several studies, no association between muscle mass and functional status was observed. Current research on the combination of obesity with poor muscle strength (dynapenic-obesity) suggests a potential additive effect of both components on poor functional status in old age which seems independent of the level of physical activity. © 2010 The Author.