Muscle strength and entheseal size in human thumbs: testing the relationship with a cadaveric model

Abstract

In this study we analyse the relationship between strength and the entheseal area of the opponens pollicis (OP) and abductor pollicis longus (APL) muscles, two muscles of the hand whose main function is to oppose the thumb and move the thumb anteriorly, respectively. We were interested in this link for two reasons: (1) to determine if muscular strength is related to entheseal size, and (2) to evaluate the predictive power of enthesis, age, sex and body size on muscular strength. With the latter objective we attempt to discuss whether it is reasonable to infer behaviour from entheses in the archaeological record. To figure out if the recruitment of muscles leaves a distinctive mark on the bone is a key component for understanding human hand evolution. This is because manipulative activities, like tool-related behaviours, could contribute to the anatomical changes in the hand of our lineage as well as explain the high dexterity we have. The ability of entheses to provide information on activity patterns has a long history of debate. Briefly, there are studies concluding that manual labour has an effect on entheseal morphology, and others stating that entheseal anatomy is strongly dependant on the biological profile of individuals (e.g. age and body size) which makes them poor behavioural indicators.