Objective: To evaluate the effects of wrist splint orthoses (WSOs) on forearm muscle activity and upper extremity/torso postures. Background: WSOs are ubiquitous in industry, but the literature as to their biomechanical effects is limited. Method: Study 1: Participants performed single-plane wrist exertions with or without a WSO while the electromyographic (EMG) activity of the flexor carpi radialis, flexor carpi ulnaris, and extensor carpi ulnaris was captured. Study 2: Participants performed simple computer jumper installation tasks with or without a WSO while upper extremity/torso postures were recorded. Results: Study 1: A significant interaction between WSOs and wrist angle was observed in the response of forearm muscles (e.g., normalized EMG of the flexor carpi radial is increased from 4.2% to 15.9% as flexion increased from 0° to 36° in the orthosis conditions, whereas in the no-orthosis condition it remained 5% at all wrist flexion angles). Study 2: WSOs were found to effect wrist, torso, and shoulder postures, with the orthoses creating a 48% decrease (36° vs. 18.6°) in wrist flexion and 80% decrease (15° vs. -3°) in ulnar deviation but at a cost of increased shoulder abduction of 22% (36.5° vs. 44.5°) and increased lateral bend of torso of 30% (6° vs. 7.8°). Conclusions: WSOs increased forearm muscle activity at large wrist deviation angles and induced awkward shoulder postures in tasks requiring significant wrist deviation. Application: Use of WSOs in occupational settings should be carefully considered relative to task requirements, as orthoses may do more harm than good.
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