Muscle performance plays a direct role in measures of physical capability, such as grip strength, and indirectly influences the ability to balance and walking speed. It is therefore hypothesised that genes involved in muscle function affect physical capability.

The protein ACTN3 is expressed in fast twitch muscle fibers and a polymorphism in ACTN3 has been linked to athletic performance (Ahmetov et al. 2008, Enyon et al 2009). Whilst some studies have investigated the association between this polymorphism and measures of physical functioning in the general population (Moran et al. 2007, Delmonico et al. 2008, Walsh et al 2008), with, for example, no associations observed with grip strength in older adults (Delmonico et al. 2008) or adolescents (Moran et al), there have also been conflicting gender differences found with regards to other physical functioning traits (Delmonico et al 2008, Walsh et al. 2008). Thus it is proposed that a larger sample size will be able to provide stronger evidence of any positive or null associations.

The objective is to use available genotypic information for ACTN3 (rs1815739/ r577X) in ALSPAC and investigate associations with measures of physical capability. The analyses will then be pooled in a meta-analysis with 7 HALCyon cohorts (www.halcyon.ac.uk) containing around 12,000 middle-aged UK men and women.