The loss of strength can become so severe it contributes to the onset of frailty and becomes the limiting factor for a person’s ability to live independently. In their prospective, longitudinal study of over 400 community-dwelling women, between 70–79 years of age, Xue et al. (2008) found weakness to be the most common initial manifestation of the frailty phenotype and moderately predictive of frailty onset. Despite its prevalence in frail older adults, the insidious course of weakness means that it is not exclusive to this cohort of older adults; strength changes have been observed in healthy, active older adults that have been characterized by large intra-individual variations and con- siderable variability compared with their younger counter- parts (Phillips et al., 1992). The inter- and intra-variability in strength changes among older adults may reflect the inter- action of non-physical factors with physical weakness. Among older adults with osteoarthritis, for example, nega- tive affect and muscle strength have demonstrated a signif- icant interaction effect on function and disability