Normalization to Maximal Voluntary Contraction is Influenced by Subacromial Pain

Abstract

In this study, we aimed to determine if electromyography (EMG) normalization to maximal voluntary isometric contractions (MVIC) was influenced by subacromial pain in patients with subacromial impingement syndrome. Patients performed MVICs in unique testing positions for each shoulder muscle tested before and after subacromial injection of local anesthetic. In addition to collection of MVIC data, EMG data during an arm elevation task were recorded before and after injection. From a visual analog pain scale, patients had a 64% decrease in pain following the injection. Significant increases in MVICs were noted in 4 of the 7 shoulder muscles tested: anterior, middle and posterior deltoid, and lower trapezius. No significant differences were noticed for the upper trapezius, latissimus dorsi, or serratus anterior. MVIC condition (pre and post injection) had a significant influence on EMG normalization for the anterior deltoid and lower trapezius muscle. Results indicate that subacromial pain can influence shoulder muscle activity, especially for the deltoid muscles and lower trapezius. In addition, normalization to MVIC in the presence of pain can have unpredictable results. Caution should be taken when normalizing EMG data to MVIC in the presence of pain.

Relation between preoperative electromyographic activity of the deltoid and upper trapezius muscle and clinical results in patients treated with reverse shoulder arthroplasty

“…Although the MVC method is commonly used for healthy subjects, the RVC method is good for patients who find it difficult to exert maximal or submaximal power because of severe joint pain. 8,20 Given the characteristics of our patients with CTA or OA with large cuff tears, it was impossible to perform MVC. Therefore, standing erect with both arms at the sides was adopted as the reference posture.…”

Normalization of the trapezius sEMG signal – a reliability study on women with and without neck-shoulder pain

“… 53 The use of maximal contractions can be a source of discomfort and also can lead to an overestimation of muscle activation. 54 The type of resistance applied during MVCs can also be a source of variability. In this study, the resistance was manually applied since this method is the most reported in the literature 38 but the use of straps is also commonly reported.…”

Electromyographic Muscle Activity and Three‐Dimensional Scapular Kinematics in Patients With Multidirectional Shoulder Instability: A Study in the Hypermobile Type of the Ehlers‐Danlos Syndrome and the Hypermobility Spectrum Disorders

“…Nevertheless, our findings should be interpreted in the light of the study limitations. First, since maximal muscle activation can cause discomfort and overestimation of muscle strength (21), caution is recommended when normalizing to an MVIC in patients with shoulder pain. To avoid overestimation of the percentage of muscle activation, MVIC tests should happen in a pain-free or reduced-pain condition (21).…”

“…After clinical examination, EMG electrodes were placed. To allow for relevant EMG comparisons between subjects and studies, it is recommended to normalize EMG activity to a maximum voluntary isometric contraction (MVIC) (21). Most hEDS/HSD patients were unable to perform the previously described MVICs (22), since many of these positions are challenging for unstable shoulders and provoke pain symptoms and apprehension.…”