An examination of the linearity and reliability of the electromyographic amplitude versus dynamic constant external resistance relationships using monopolar and bipolar recording methods

The purpose of this study was to examine the linearity and reliability of the electromyographic (EMG) amplitude versus dynamic constant external resistance (DCER) relationships for monopolar and bipolar recording techniques during concentric and eccentric muscle actions. Nineteen healthy men (mean ± SD age = 22.9 ± 2.5 years) performed a series of randomly ordered, submaximal to maximal, unilateral DCER muscle actions of the dominant forearm flexors on two occasions separated by at least 48 h. Specifically, the subjects lifted and lowered weights corresponding to 10–100% of the one repetition maximum (1-RM) in 10% increments. During each muscle action, monopolar and bipolar surface EMG signals were detected simultaneously from the biceps brachii. For the monopolar and bipolar methods, the coefficients of determination for the EMG amplitude versus DCER relationships ranged from 0.64–0.98 and 0.38–0.98 for the concentric muscle actions and 0.45–0.98 and 0.45–0.98 for the eccentric muscle actions, respectively. The intraclass correlation coefficients (ICC) and corresponding standard errors of measurement (SEM) for the linear slope coefficients for the EMG amplitude versus DCER relationships were 0.682 (18.4%) and 0.594 (21.8%) with the monopolar method and 0.810 (25.6%) and 0.774 (17.6%) with the bipolar method for the concentric and eccentric muscle actions, respectively. These findings indicated that monopolar and bipolar recording techniques may be used with a similar degree of linearity and reliability for the EMG amplitude versus concentric and eccentric DCER relationships.

Research highlights▶ Monopolar and bipolar recording techniques may be used with a similar degree of linearity and reliability when examining the EMG amplitude versus concentric and eccentric DCER relationships. ▶ Consistent with previous studies, the absolute EMG amplitude values for the monopolar recording technique were greater than those for the bipolar method from 10–100% 1-RM for both concentric and eccentric DCER muscle actions. ▶ When examining the reliability of absolute EMG amplitude values, concentric muscle actions may provide more consistent results than eccentric muscle actions, especially with a bipolar recording technique. ▶ With further validation, it may be possible to use DCER muscle actions to examine the mechanisms underlying strength gains in strength and conditioning and/or physical therapy settings.