The forearm positioning changes electromyographic activity of upper limb muscles and handgrip strength in the task of...

The aim of the present study was to analyse the electromyographic activity of the upper limb muscles as well as the handgrip strength during the activity of pushing a load cart. Eighteen healthy male right-handed volunteers (21.50 ± 2.77 years old) took part in the study. Electrodes were placed on upper trapezius fibres, brachial biceps, brachial triceps, and extensors and flexors of wrist and fingers. The original handle of the load cart was replaced by two handgrip systems mounted on load cells, thus allowing the handgrip strength to be measured according to the wrist position variation, that is, wrists in neutral position with pronated forearm (WN-PF) or in ulnar deviation with forearm in neutral position (WUD-NF). The signals generated by the load cells during manoeuvre of the load cart and the electromyographic signals were simultaneously captured. Signal processing was performed by using a specific routine developed for analysis of root mean square (RMS) and median frequency (MF). Greater handgrip strength occurred in WN-PF position. In maximal isometric contraction, the RMS of the flexors and extensors showed greater electromyographic activity in WN-PF (intra-muscles) and extensors position (inter-muscles). Decreased handgrip strength in the latter stages of the circuit, with variation of the RMS and MF of all muscles tested. One can conclude that electromyographic activity and handgrip strength are both affected during the phases of an elliptical displacement of the load cart.