Maximal voluntary isometric contraction tests for normalizing electromyographic data from different regions of supraspinatus and infraspinatus muscles: Identifying reliable combinations

Abstract

This study aimed to identify optimal sets of maximal voluntary isometric contractions (MVICs) for normalizing EMG data from anterior and posterior regions of the supraspinatus, and superior, middle and inferior regions of the infraspinatus. 31 right-handed young healthy individuals (15 males, 16 females) participated. EMG activity was obtained from two regions of supraspinatus and three regions of infraspinatus muscles via fine wire electrodes. Participants performed 15 MVIC tests against manual resistance. The EMG data were normalized to the maximum values. Optimal sets of MVIC combinations, defined as those which elicited >90% MVIC activation in the muscles of interest in >80% and >90% of the population, were obtained. EMG data from the inferior region of infraspinatus were removed from analysis due to technical problem. No single test achieved maximal activation of both regions of either the supraspinatus or infraspinatus. Instead, a combination of 6-8 MVICs were required to reach >90% MVIC activation in both parts of those muscles. In all regions of the rotator cuff muscles, the optimal combination was obtained with 8-10 MVICs. The proposed combinations can reduce inter-participant variability in generating maximal activation from different regions of the supraspinatus and infraspinatus muscles.

Shoulder scaption is dependent on the behavior of the different partitions of the infraspinatus muscle

“…These results coincide with the activity values in the middle partition observed in our study. Some investigators measured independent activation of those partitions using EMG, and concluded that the muscle partitions have different roles [ 1 , 2 , 4 , 14 ]. However, EMG measurements from the partitions were not obtained during scaption, rather during specific positions, e.g.…”

“…While EMG and kinematic evaluations have been adopted for assessing muscular function, the former is invasive and has not been successfully implemented in the inferior partition due to wire displacement [ 1 ], and the latter has not been applied in the various muscular partitions. In our study, we successfully discriminated the spatio-temporal relationship of the three partitions of the ISP muscle during scaption using SWE.…”

“…While some investigators tried to measure independent activations of the partitions of the ISP muscle using EMG, it is difficult to measure the activation of each partition, especially in the inferior partition, throughout various shoulder motions as the fine wires can be displaced out of the muscle during contraction [ 1 , 2 , 4 , 14 ]. Shear-wave ultrasound elastography (SWE) has been previously implemented to measure shear modulus of muscles, as a surrogate for muscle stiffness.…”

Relationship between Skin Temperature, Electrical Manifestations of Muscle Fatigue, and Exercise-Induced Delayed Onset Muscle Soreness for Dynamic Contractions: A Preliminary Study

“…A small piece of athletic tape was used to prevent the electrode and wireless transmitter from moving [ 32 ]. A maximal voluntary isometric contraction for elbow flexion at approximately 90° was performed against manual resistance from one researcher before the exercise protocol started in order to provide the data for EMG normalization [ 33 , 34 , 35 ].…”

Isolated Activation of the Infraspinatus Muscle in Four Manual Muscle Testing Positions

“…Several studies have been conducted to identify methods to normalize the infraspinatus muscle 7,12 . However, there has been no attempt to investigate the optimal MVIC test position for the isolation of the infraspinatus muscle.…”