Measurement of angular wrist neutral zone and forearm muscle activity

OBJECTIVES: To determine the forearm muscles activity in different wrist deviated positions and wrist neutral zone, and to assess the self-selected resting position without visual feedback. BACKGROUND: Wrist deviation occurs in almost all industrial and office jobs. This has been deemed hazardous for carpal tunnel syndrome. Proper resting wrist position is likely to decrease the hazard for carpal tunnel pressure. METHODS: Twenty blindfolded subjects without history of hand/forearm musculoskeletal disorders participated in the study. The EMG of the forearm muscles (flexor carpi radialis, flexor carpi ulnaris, extensor carpi radialis and, extensor carpi ulnaris) in deviated and neutral wrist postures was recorded at a sampling rate of 1 kHz. Also, wrist neutral zone at rest was measured using a custom-made calibrated uniaxial electrogoniometer. One-way ANOVA with repeated measures was used in order to find the impact of wrist deviation on muscles activity. RESULTS: The participants positioned their wrist in rest at 7 degrees -9 degrees extension and 5 degrees -7 degrees ulnar deviation. Significantly higher EMG activity was recorded for each muscle in the wrist deviated postures when compared to neutral position (P < 0.001). CONCLUSIONS: Self selected wrist neutral posture decreased the muscle activity significantly. Placement of wrists in neutral zone is expected to reduce risk of injuries.