The roles of whole body balance, shoe-floor friction and joint strength during maximum exertions: searching for the "weakest link".

Exerting manual forces is critical during occupational performance. Therefore, being able to estimate maximum force capacity is particularly useful for determining how these manual exertion demands relate to available capacity. To facilitate this type of prediction requires a complete understanding of how maximum force capacity is governed biomechanically. This research focused on identifying how factors including joint moment strength, balance and shoe-floor friction affected hand force capacity during pulling, pressing downward and pushing medially. To elucidate potential limiting factors, joint moments were calculated and contrasted with reported joint strength capacities, the balancing point within the shoe-floor interface was calculated and expressed relative to the area defined by the shoe-floor interface, and the net applied horizontal forces were compared with the available friction. Each of these variables were calculated as participants exerted forces in a series of conditions designed to systematically control or restrict certain factors from limiting hand force capacity. The results demonstrated that hand force capacity, in all tested directions, was affected by the experimental conditions (up to 300%). Concurrently, biomechanical measures reached or surpassed reported criterion thresholds inferring specific biomechanical limitations. Downward exertions were limited by elbow strength, whereas pulling exertions were often limited by balance along the anterior-posterior axis. No specific limitations were identified for medial exertions.