The effect of two types of maximal voluntary contraction and two electrode positions in field recordings of forearm extensor muscle activity during hotel room cleaning.

PURPOSE: To investigate the effects of using hand grip or resisted wrist extension as reference contraction, and two electrode positions, on field recordings of forearm extensor muscle activity.

MATERIALS AND METHODS: The right forearm extensor muscle activity was recorded using two pairs of electrodes (over the most prominent part; position 2 and proximal to that; position 1) during one working day in 13 female hotel housekeepers. Each subject performed the two maximal voluntary contractions (MVCs), and the electrical activity obtained during these (the maximal voluntary electrical activity; MVE) was used for normalisation. Each set of recordings was analysed twice, once using hand grip as MVC and once using resisted wrist extension.

RESULTS: Resisted wrist extension showed higher group mean MVE than hand grip. Position 2 had higher correlation between MVE and force during the MVCs. The workload during cleaning was lower when using resisted wrist extension as the reference than when using hand grip (24%MVE versus 46%MVE; p = 0.002 at position 2) for the 90th percentile. The workload (99th percentile) was overestimated in two subjects when using hand grip as reference.

CONCLUSIONS: Problems associated with poorly activated forearm extensors can be overcome by using resisted wrist extension as reference.