Reproducibility of surface EMG during dynamic shoulder forward flexions: a study of clinically healthy subjects

Electromyographic Analysis of Shoulder Neuromuscular Activity in Women Following Breast Cancer Treatment: A Cross-Sectional Descriptive Study

Certain secondary effects derived from medical treatment in breast cancer can favor the development of alterations in shoulder biomechanics. To the best of our knowledge, persistent peripheral pain as a key factor for the development of neuromuscular activity impairments has not been analyzed. A cross-sectional descriptive study was carried out. A total of 90 women were included and allocated to three groups: (i) 30 women with persistent peripheral pain after breast cancer treatment, (ii) 30 women without pain after breast cancer treatment, and (iii) 30 healthy women. Surface electromyography was employed to measure the onset and amplitude of the muscle activity of three shoulder movements. Statistically significant differences were found in the neuromuscular activity for all the muscles and shoulder movements among women with persistent pain versus healthy women (i.e., amplitude muscle activity variable p < 0.001). Statistically significant differences were also observed in the neuromuscular activity for certain muscles in shoulder movements among women with persistent pain versus women without pain, as well as between women without pain versus healthy women. Therefore, following breast cancer treatment, women showed alterations in their shoulder neuromuscular activity, which were more significant if persistent pain existed. These findings may contribute to developing a selective therapeutic exercise program that optimizes the shoulder neuromuscular activity in women after breast cancer treatment.

Intra-session and Inter-day Reliability of the Myon 320 Electromyography System During Sub-maximal Contractions

Electromyography systems are widely used within the field of scientific and clinical practices. The reliability of these systems are paramount when conducting research. The reliability of Myon 320 Surface Electromyography System is yet to be determined. This study aims to determine the intra-session and inter-day reliability of the Myon 320 Surface Electromyography System. Muscle activity from fifteen participants was measured at the anterior deltoid muscle during a bilateral front raise exercise, the vastus lateralis muscle during a squat exercise and the extensor carpi radialis brevis (ECRB) muscle during an isometric handgrip task. Intra-session and inter-day reliability was calculated by intraclass correlation coefficient, standard error of measurement and coefficient of variation (CV). The normalized root mean squared (RMS) surface electromyographic signals produced good intra-session and inter-day testing intraclass correlation coefficient values (range: 0.63–0.97) together with low standard error of measurement (range: 1.49–2.32) and CV (range: 95% Confidence Interval = 0.36–12.71) measures for the dynamic-and-isometric contractions. The findings indicate that the Myon 320 Surface Electromyography System produces good to fair reliability when examining intra-session and inter-day reliability. Findings of the study provide evidence of the reliability of electromyography between trials which is essential during clinical testing.

Reliability of telemetric electromyography and near-infrared spectroscopy during high-intensity resistance exercise

This study quantified the inter- and intra-test reliability of telemetric surface electromyography (EMG) and near infrared spectroscopy (NIRS) during resistance exercise. Twelve well-trained young men performed high-intensity back squat exercise (12 sets at 70-90% 1-repetition maximum) on two occasions, during which EMG and NIRS continuously monitored muscle activation and oxygenation of the thigh muscles. Intra-test reliability for EMG and NIRS variables was generally higher than inter-test reliability. EMG median frequency variables were generally more reliable than amplitude-based variables. The reliability of EMG measures was not related to the intensity or number of repetitions performed during the set. No notable differences were evident in the reliability of EMG between different agonist muscles. NIRS-derived measures of oxyhaemoglobin, deoxyhaemoglobin and tissue saturation index were generally more reliable during single-repetition sets than multiple-repetition sets at the same intensity. Tissue saturation index was the most reliable NIRS variable. Although the reliability of the EMG and NIRS measures varied across the exercise protocol, the precise causes of this variability are not yet understood. However, it is likely that biological variation during multi-joint isotonic resistance exercise may account for some of the variation in the observed results.

Scapular bracing and alteration of posture and muscle activity in overhead athletes with poor posture

CONTEXT

Overhead athletes commonly have poor posture. Commercial braces are used to improve posture and function, but few researchers have examined the effects of shoulder or scapular bracing on posture and scapular muscle activity.

OBJECTIVE

To examine whether a scapular stabilization brace acutely alters posture and scapular muscle activity in healthy overhead athletes with forward-head, rounded-shoulder posture (FHRSP).

DESIGN

Randomized controlled clinical trial.

SETTING

Applied biomechanics laboratory.

PATIENTS OR OTHER PARTICIPANTS

Thirty-eight healthy overhead athletes with FHRSP.

INTERVENTION(S)

Participants were assigned randomly to 2 groups: compression shirt with no strap tension (S) and compression shirt with the straps fully tensioned (S + T). Posture was measured using lateral-view photography with retroreflective markers. Electromyography (EMG) of the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) in the dominant upper extremity was measured during 4 exercises (scapular punches, W's, Y's, T's) and 2 glenohumeral motions (forward flexion, shoulder extension). Posture and exercise EMG measurements were taken with and without the brace applied.

MAIN OUTCOME MEASURE(S)

Head and shoulder angles were measured from lateral-view digital photographs. Normalized surface EMG was used to assess mean muscle activation of the UT, MT, LT, and SA.

RESULTS

Application of the brace decreased forward shoulder angle in the S + T condition. Brace application also caused a small increase in LT EMG during forward flexion and Y's and a small decrease in UT and MT EMG during shoulder extension. Brace application in the S + T group decreased UT EMG during W's, whereas UT EMG increased during W's in the S group.

CONCLUSIONS

Application of the scapular brace improved shoulder posture and scapular muscle activity, but EMG changes were highly variable. Use of a scapular brace might improve shoulder posture and muscle activity in overhead athletes with poor posture.

Task-Dependent Modulation of Inputs to Proximal Upper Limb Following Transcranial Direct Current Stimulation of Primary Motor Cortex

Cathodal transcranial DC stimulation (c-tDCS) suppresses excitability of primary motor cortex (M1) controlling contralateral hand muscles. This study assessed whether c-tDCS would have similar effects on ipsi- and contralateral M1 projections to a proximal upper limb muscle. Transcranial magnetic stimulation (TMS) of left M1 was used to elicit motor evoked potentials (MEPs) in the left and right infraspinatus (INF) muscle immediately before and after c-tDCS of left M1, and at 20 and 40 min, post-c-tDCS. TMS was delivered as participants preactivated each INF in isolation (left, right) or both INF together (bilateral). After c-tDCS, ipsilateral MEPs in left INF and contralateral MEPs in right INF were suppressed in the left task but not in the bilateral or right tasks, indicative of task-dependent modulation. Ipsilateral silent period duration in the left INF was reduced after c-tDCS, indicative of altered transcallosal inhibition. These findings may have implications for the use of tDCS as an adjunct to therapy for the proximal upper limb after stroke.

Reliability of different thresholds for defining muscular rest of the trapezius muscles in computer office workers

This study aimed at documenting the reliability of different thresholds used for defining the muscular rest of the trapezius muscles of 27 computer office workers, using surface electromyography (EMG) signals collected in the field. Measurement strategies for increasing the reliability of the results were also explored. Ten different thresholds to define muscular rest were compared: 1) five normalised (individualised) thresholds; 2) three absolute thresholds (in muV); 3) two absolute but individualised thresholds. The reliability was assessed using both a 15-min standardised computer task and 45 min of regular computer work. The main findings were: 1) overall, in a repeated measures study design, muscular rest variables were more reliable with the use of absolute thresholds when compared to normalised and individualised thresholds; 2) excellent reliability (index of dependability >0.75) can be reached when averaging the scores over 2 days; 3) using a standardised task instead of regular work does not necessarily lead to more reliable results.

Fatigue during prolonged intermittent overhead work: reliability of measures and effects of working height

Shoulder pain is prevalent among industrial workers and existing evidence supports that overhead work is an important specific risk factor. Existing guidelines are limited, with overhead work typically recommended to be avoided, and research on overhead work has been mixed in terms of the effects of increasing arm reach. A laboratory-based simulation of overhead work was conducted, at three working heights, in order to facilitate improved guidelines and to identify potential non-linear effects of overhead work height. Several indicators of shoulder fatigue served as outcome measures and a preliminary study was performed to assess the reliability of several of these measures. Fatigue measures based on electromyography (EMG) generally had low reliability, whereas excellent reliability was exhibited for ratings of perceived discomfort (RPD). Consistent with this, no effects of overhead work height were found on EMG-based measures, yet clear non-linear effects were found on RPD and task performance. The source of the effects of work height appeared to be related to a combination of muscle activation levels and demands on precision/control at the highest location. These results support the utility of subjective measures for relatively low-level intermittent exertions and demonstrate increasingly detrimental fatigue and performance effects at extremes in reach during overhead work.

Assessment of upper extremity muscle function in persons with tetraplegia

The objective was to investigate the actual level of muscle function impairment in tetraplegic persons and, inextricably related to this, the possibilities to compensate function loss using new muscle coalitions. In this cross-sectional group study, 20 persons with a cervical spinal cord injury (SCI) at segmental levels C5C6 or C7C8 and 10 control persons participated. Activity from 21 upper extremity and trunk muscles was recorded during standardised gross upper extremity task performance. No substantial differences in main activation patterns were found between C7C8 and control subjects. In contrast, main activation patterns in C5C6 persons showed an absence of selectivity, which may be explained by the participants activating every controllable muscle in an attempt to perform maximally. In order to identify more intricate differences in muscle activation between control and C7C8 persons a fine motor function task may be necessary. Muscle activation patterns during arm task performance were stable in all three groups.

Test-retest reliability of EMG and peak torque during repetitive maximum concentric knee extensions

The aim of this study was to investigate the reliability of peak torque and surface electromyography (EMG) variable's root mean square (RMS) and mean frequency (MNF) during an endurance test consisting of repetitive maximum concentric knee extensions. Muscle fatigue has been quantified in several ways, and in isokinetic testing it is based on a set of repetitive contractions. To assess test-retest reliability, two sets of 100 dynamic maximum concentric knee extensions were performed using an isokinetic dynamometer. The two series were separated by 7-8 days. The subjects relaxed during the passive flexion phase. Twenty (10 men and 10 women) clinically healthy subjects volunteered. Peak torque and EMG from rectus femoris, vastus medialis, vastus lateralis and biceps femoris were recorded. RMS and MNF were calculated from the EMG signal. The reliability was calculated with intraclass correlation coefficient ICC (1.1) and standard error of measurements (SEM). The reliability of peak torque was good (ICC=0.93) and SEM showed low values. ICC was good for absolute RMS of rectus femoris (ICC>/=0.80), vastus medialis (ICC>/=0.88) and vastus lateralis (ICC>/=0.82) and MNF of rectus femoris (ICC>/=0.82) and vastus medialis (ICC>/=0.83). Peak torque, and MNF and RMS of rectus femoris and vastus medialis are reliable variables obtained from an isokinetic endurance test of the knee extensors.

Generalizability of trunk muscle EMG and spinal forces

The generalizability of trunk muscle EMG and spinal loading estimates obtained from an EMG-assisted biomechanical model was assessed over three occasions and three repetitions. The greatest sources of variability consisted of the intersubject differences and the interaction between subject and occasion. The ID (reliability coefficient) was less for trunk muscle activity compared with estimates of anteroposterior shear force, compression force, and gain computed from the biomechanical model. In order to obtain an ID of 0.8, we recommend five testing occasions for submaximal EMG measurements and three testing occasions for biomechanical estimates. Reproducible estimates of maximal trunk extensor EMG could not be obtained within five testing occasions and five repetitions. Although many recruitment patterns could cause the same extension torque output, their net effect on internal loading seems to be less variable than the underlying measurements.