Upper extremity biomechanics in native and non-native signers

Individuals fluent in sign language (signers) born to non-signing, non-deaf parents (non-natives) may have a greater injury risk than signers born to signing, deaf parents (natives). A comprehensive analysis of movement while signing in natives and non-natives has not been completed and could provide insight into the greater injury prevalence of non-natives. OBJECTIVE: The objective of this study was to determine differences in upper extremity biomechanics between non-natives and natives. METHODS: Strength, 'micro' rests, muscle activation, ballistic signing, joint angle, and work envelope were captured across groups. RESULTS: Non-natives had fewer rests (p=0.002) and greater activation (p=0.008) in non-dominant upper trapezius. For ballistic signing, natives had greater anterior-posterior jerk (p=0.033) and for joint angle, natives demonstrated greater wrist flexion-extension range of motion (p=0.040). Natives also demonstrated greater maximum medial-lateral (p=0.015), and greater minimum medial-lateral (p=0.019) and superior-inferior (p=0.027) positions. CONCLUSIONS: We observed that natives presented with more rests and less activation, but greater ballistic tendencies, joint angle, and envelope compared to non-natives. Additional work should explore potential links between these outcomes and injury risk in signers.