Effects of handle orientation, gloves, handle friction and elbow posture on maximum horizontal pull and push forces

Biomechanical models were evaluated for effects of handle orientation, handle material, gloves and arm posture on maximal pull/push force. Eight healthy subjects performed maximum pull/push exertions on handles with two different orientations and two different surface materials, using bare hand and two types of glove as well as two arm postures. The empirical data supported the proposed biomechanical models: Pull/push forces for the bare hand on a rubber handle decreased 10% when the handle was parallel to the pull/push direction, compared with when perpendicular to it. For parallel handles, pull/push forces further decreased with decreasing hand-handle friction coefficient (simulated by different handle materials and gloves). Pull force exerted by the bare hand was 29% greater when the elbow was extended than when flexed. Pull force was greater than push force (with bare hand and flexed elbow). The biomechanical models suggest that friction between the hand and handle limits pull/push forces for parallel handles. Elbow strength may be responsible for decreased pull force for the flexed elbow posture and decreased force for pull compared with push in the postures examined. STATEMENT OF RELEVANCE: Biomechanical models presented in this paper provide insights for causes of upper extremity strength limitations during pull/push tasks. Findings in this paper can be used directly in the design of workstation and objects to reduce fatigue and risk of musculoskeletal disorders.