title: Getting a Handle on Handles: A Biomechanical Investigation of the Efficiency Hypothesis of Hafted Tool Technology
Creators: name: Coe, Dominic
Publisher: name: University of Liverpool Repository
Year: 2023

description: It is widely acknowledged that the transition from hand-held to hafted tool technology marked a significant shift in conceptualising the construction and function of tools. Amongst other benefits, hafting is thought to have given its users a significant biomechanical and physiological advantage in undertaking basic subsistence related tasks when compared to the long-established tradition of tools made to be used directly in the hand. It is assumed that the addition of a handle improved the (bio)mechanical properties of a tool and upper limb by offering greater amounts of leverage, force and precision. As a consequence, the use of hafted tools should, in theory, have reduced the biomechanical and physiological stresses required to complete a task compared to that of a hand-held equivalent. This proposed reduction in demands placed upon the body, and in particular the upper limb, is proposed to correspond with differences in upper limb morphology, and trends in the reduction of body mass and skeletal robusticity in the genus Homo (Barham, 2013; Churchill, 2001). These series of linked assumptions have been consolidated into the ‘Efficiency Hypothesis of hafted tool technology’ (Barham, 2013). Building on the pilot study of Coe (2015), this study represents the first systematic attempt to test the propositions of the efficiency hypothesis and wider assumptions about the biomechanical benefits of hafted tools. A controlled laboratory framework was employed to collect data from upper limb kinematics, selected upper limb electromyography and whole body respirometry of 40 (23 male, 17 females) physically fit, healthy participants when completing two subsistence activities (chopping and scraping). In one condition, participants completed the tasks using hafted tools. The results were then compared to participants’ performance when completing the same task when using hand-held tools. Overall, results show significant differences in kinematics, electromyography and respirometry in both chopping and scraping tasks. The hafted condition elicited greater ranges of motion, greater muscle activity, greater net energy expenditure (EE) and reduced cost of activity energy expenditure (CoA EE) compared to the hand-held condition in both tasks. These differences were seen to be greater in the chopping task, compared to the scraping task. Most notably, in the chopping task, the hafted tool prompted the use of a Proximal-to-Distal Joint Sequence (PDJS) and a Dart Thrower’s Motion (DTM) at the wrist. These two well-known biomechanical strategies help to produce large velocities at the distal end of the limb without requiring heavy muscular effort. The scraping task, although reduced, shows significant differences in kinematics and EMG, likely allowing for greater force to be applied and ensuring an energetic benefit. The precise mechanisms and biomechanical strategies that elicit this remain unclear in scraping. This study also revealed some unexpected sex differences in muscle activity and net energy use. In electromyography, female participants produced statistically greater muscle activity magnitudes compared to males. Whereas males tended to use more energy compared to females, most notably during the hafted condition. Overall, it has been shown that from an energetic perspective, the hafted tools did indeed offer a significant benefit to the user in both tasks, however, the mechanisms by how this efficiency occurs were surprisingly different from those predicted by the efficiency hypothesis. Directions of future research are outlined that build on this pioneering first effort to assess the benefits of hafting.