MUSCLE ACTIVATION AND DETERMINATION OF ELECTROMYOGRAPHIC FATIGUE THRESHOLD DURING INCREMENTAL LOAD TEST IN ARM ERGOMETER: A PILOT STUDY

Abstract

The aim of this study was to assess the activation of four muscles of the upper limb (Biceps Brachii [BB], Triceps Brachii [TB], Anterior Deltoid [AD] and Posterior Deltoid [PD]) and determine the electromyographic fatigue threshold (EMGth) during an incremental test on an arm ergometer. Four male volunteers (age: 25.25 ± 4.7, height: 173 ± 4 cm, body mass: 71.5 ± 6.3 kg) performed an incremental test with an approximate cadence of 80 rpm until they reach the maximum power output of the ergometer (load increments of 3-4 W every 4 min, starting with 19 W and ending at 48 W). The electromyographic signal (EMG) was collected during the tests (Myosystem 2000 Noraxon, USA) and subsequently treated using the program MATLAB 7.7.0 (correction and calculation of RMS). The EMGth was detected from visual inspection. Values of heart rate (HR) were also recorded at the end of each stage. There was great variation in muscle activation between the muscles examined during the incremental test. AD, PD and TB had a decreasing behavior of the EMG signal, however, BB showed an increase during the test. The EMGth was found only in the BB muscle (power: 44 W, HR: 123 bpm) of one subject, representing approximately 90% of the maximum power of the ergometer. Our results suggest that increasing the workload on the cyclical movement required by the bilateral arm ergometer caused a compensatory action evidenced by increased activation of BB and decreased of TB. Already the decay of activation of stabilizing muscles of the shoulder (DA and DP) can be associated with signs of peripheral fatigue and / or use of the torque generated by the BB.. This study also shows that BB is the muscle most likely to reach the EMGth in an incremental test.