Comparing two methods to record maximal voluntary contractions and different electrode positions in recordings of forearm extensor muscle activity: Refining risk assessments for work-related wrist disorders

BACKGROUND Wrist disorders are common in force demanding industrial repetitive work. Visual assessment of force demands have a low reliability, instead surface electromyography (EMG) may be used as part of a risk assessment for work-related wrist disorders. For normalization of EMG recordings, a power grip (hand grip) is often used as maximal voluntary contraction (MVC) of the forearm extensor muscles. However, the test-retest reproducibility is poor and EMG amplitudes exceeding 100% have occasionally been recorded during work. An alternative MVC is resisted wrist extension, which may be more reliable. OBJECTIVE To compare hand grip and resisted wrist extension MVCs, in terms of amplitude and reproducibility, and to examine the effect of electrode positioning. METHODS Twelve subjects participated. EMG from right forearm extensors, from four electrode pairs, was recorded during MVCs, on three separate occasions. RESULTS The group mean EMG amplitudes for resisted wrist extension were 1.2-1.7 times greater than those for hand grip. Resisted wrist extension showed better reproducibility than hand grip. CONCLUSIONS The results indicate that the use of resisted wrist extension is a more accurate measurement of maximal effort of wrist extensor contractions than using hand grip and should increase the precision in EMG recordings from forearm extensor muscles, which in turn will increase the quality of risk assessments that are based on these.