The aims of the proposed Research Fellowship are as follows: 1. To describe a lifecourse grip strength trajectory from childhood to old age, by combining data from several UK cohorts 2. To compare the influence of physical activity on grip strength at different ages across the lifecourse 3. To explore the relationship between physical activity and subsequent grip strength trajectory. Evidence, mainly from age-heterogenous cross-sectional studies1 suggest that muscle strength, as assessed by grip strength, increases through childhood and adolescence, reaching a peak in early adult life before declining with increasing age. As no one cohort has repeated measures of strength for the same individuals from childhood to old age, it is necessary to combine repeated measures from several cohorts in order to construct a lifecourse trajectory of muscle strength. The cross-council funded HALCyon cohort consortium has already harmonised measures of physical capability, including grip strength, in eight UK cohorts spanning ages 50-90+ years.2 Similarly, the FALCon project has worked to develop and disseminate methods for the lifecourse modelling of physical and cognitive function, as well as cardiovascular function such as blood pressure.3 There is therefore the opportunity to continue work from both projects to look at the lifecourse trajectory of grip strength. In childhood and adolescence, we hypothesise that higher levels of CPA may predict a higher absolute values of muscle strength as well as a greater relative increase in strength towards the subsequent peak in early adult life. We also hypothesis that higher levels of CPA will be prospectively associated with slower declines in muscle strength in adulthood.