Muscle Activity Balance Research Articles

Effects of Using a Special Weighted Vest on Muscle Activity around the Scapula during Knee Push-Up Plus in Healthy Subjects.

Electromyography assessed scapular muscle activity in 32 healthy adults (15 males, 17 females) during three KPUP variations. PM and UT showed no significant activity differences across loads, whereas SA and LT did. SA activity was significantly higher in the weighted KPUP (WKPUP) 3 kg than that in KPUP and WKPUP 1 kg. LT activity was also significantly higher in WKPUP 3 kg compared to KPUP and WKPUP 1 kg, with KPUP showing higher activity than WKPUP 1 kg. PM/SA ratios remained consistent across loads, while UT/LT ratios varied significantly, being notably lower at 3 kg compared to 0 kg and 1 kg. Similarly, UT/SA ratios differed significantly among loads, being notably lower at 3 kg and 1 kg compared to 0 kg. WKPUP with 3 kg demonstrated significantly higher SA and LT activity compared to KPUP and WKPUP 1 kg. The lowest UT/LT ratio was observed during the WKPUP 3 kg, suggesting its effectiveness for optimizing muscle activation balance during KPUP exercises. These findings may inform the development of exercise protocols aimed at improving scapular stabilization.

Normal values of scapular muscle activity ratio during arm elevation and the relationship to muscle strength and sex difference.

The normal value of the scapular muscle activity ratio during arm elevation is not clear. To obtain normal values of the scapular muscle activity ratio during arm elevation in healthy individuals. This cross-sectional study enrolled 47 healthy people. The participants performed shoulder flexion and lowered task with 90-degree movements every 2 seconds. Muscle activities of scapular muscles were measured. For normalization, the maximum isometric contraction of the shoulder flexion was measured at 90∘ (reference contraction). The integrated electromyographic value (IEMG) obtained during the task was normalized by IEMG during the reference contraction and the relative IEMG value was calculated. Then, the scapular muscle activity ratio was computed. The relationship between muscle strength and other factors was also investigated. The median values for upper trapezius/serratus anterior and upper trapezius/lower trapezius were often approximately 1, and that for upper trapezius/middle trapezius was often between 1 and 2. The shoulder flexion isometric strength and scapular muscle activity ratio showed significant negative correlations in multiple phases. Normal values for upper trapezius/serratus anterior and upper trapezius/lower trapezius during arm elevation and lowering were generally 1. Low muscle strength may contribute to an abnormal scapular muscle activity balance.

Masticatory performance is influenced by masticatory muscle activity balance and the cumulative occlusal contact area

ObjectiveTo investigate the influence of masticatory muscle activity balance, occlusal contact area balance and the area of occlusal contact on masticatory performance in healthy dentate adults. DesignThis cross-sectional study included ninety-three healthy subjects with complete dentition. Surface electromyography (sEMG) was used to record bilateral anterior temporalis activity and masseter muscle activity during maximum voluntary clenching and while chewing a test food. Seven levels of area of occlusal contact and near contact (ACNC) were registered and calculated cumulatively. The percentage overlapping coefficients were calculated for both muscle groups at maximum voluntary clenching and chewing and all levels of ACNC. Masticatory performance was measured by determining the median particle size of frankfurter sausage after 15 chewing cycles. Pearson’s correlation and stepwise multiple linear regression analyses were used to assess the correlations between variables and the influence of the variables on masticatory performance, respectively, at the 0.05 level of significance. ResultsMuscle balance during clenching and chewing, all near contact levels of cumulative ACNC and ACNC balance correlated negatively with median particle size (P < 0.05). The model based on stepwise multiple linear regression analysis showed muscle balance during clenching and cumulative ACNC at < 250 μm influenced median particle size. ConclusionMasticatory muscle activity balance during maximum voluntary clenching and the cumulative amount of near contact area were associated with masticatory performance, suggesting the amount of occlusal contact area—as well the balance of masticatory muscle activity—play a role in masticatory performance.

Effects of In-Shoe Midsole Cushioning on Leg Muscle Balance and Co-Contraction with Increased Heel Height During Walking.

The midsole is an essential assembly of footwear for retaining the shape of the shoe, delivering support to the foot, and serving as a cushioning and stability device for walking. To improve leg muscle balance and muscle co-contraction, we propose a new midsole design for high heels with different hardness levels at the forefoot region. Five healthy women participated in the study, with a mean ± SD age of 21.80 ± 4.09 years, and duration of high-heeled shoe wear of 5.20 ± 4.09 years. Two midsole conditions, control and multiple-hardness midsole (MHM), with heel heights of 2 (flat), 5, and 8 cm were used. The main outcome measures were to examine the acute effects of MHM by electromyography on muscle activity balance and co-contraction at varying heel heights during shuttle walk. Use of the MHM significantly reduced the muscle activity ratio between the medial and lateral gastrocnemius muscles ( P = .043) during push-off to heel strike with a heel height of 5 cm (-22.74%) and heel strike to midstance with a heel height of 8 cm (-22.26%). The increased co-contraction indices of the tibialis anterior-peroneus longus muscles (14.35% with an 8-cm heel height) and tibialis anterior-soleus muscles (15.18% with a 5-cm heel height) are significant ( P = .043), with a large effect size ( d = 0.8). These results deliver important implications in advancing the engineering of MHM design without changing the in-shoe volume to enhance leg muscle balance and co-contraction during walking.

Muscle Synergies Control during Hand-Reaching Tasks in Multiple Directions Post-stroke.

Purpose: A muscle synergies model was suggested to represent a simplifying motor control mechanism by the brainstem and spinal cord. The aim of the study was to investigate the feasibility of such control mechanisms in the rehabilitation of post-stroke individuals during the execution of hand-reaching movements in multiple directions, compared to non-stroke individuals.Methods: Twelve non-stroke and 13 post-stroke individuals participated in the study. Muscle synergies were extracted from EMG data that was recorded during hand reaching tasks, using the NMF algorithm. The optimal number of synergies was evaluated in both groups using the Variance Accounted For (VAF) and the Mean Squared Error (MSE). A cross validation procedure was carried out to define a representative set of synergies. The similarity index and the K-means algorithm were applied to validate the existence of such a set of synergies, but also to compare the modulation properties of synergies for different movement directions between groups. The similarity index and hierarchical cluster analysis were also applied to compare between group synergies.Results: Four synergies were chosen to optimally capture the variances in the EMG data, with mean VAF of 0.917 ± 0.034 and 0.883 ± 0.046 of the data variances, with respective MSE of 0.007 and 0.016, in the control and study groups, respectively. The representative set of synergies was set to be extracted from movement to the center of the reaching space. Two synergies had different muscle activation balance between groups. Seven and 17 clusters partitioned the muscle synergies of the control and study groups. The control group exhibited a gradual change in the activation in the amplitude in the time domain (modulation) of synergies, as reflected by the similarity index, whereas the study group exhibited consistently significant differences between all movement directions and the representative set of synergies. The study findings support the existence of a representative set of synergies, which are modulated to execute movements in different directions.Conclusions: Post-stroke individuals differently modulate the activation of synergies to different movement directions than do non-stroke individuals. The conclusion was supported by different muscle activation balances, similarity values and different classifications of synergies among groups.

Thumb-Rest Position and its Role in Neuromuscular Control of the Clarinet Task

Musicians spend long hours of practice and performance to master their instrument. Clarinet players support their roughly 2-lb instrument on the right-hand thumb, which results in cumulative static loading of the arm. This posture in turn can cause discomfort and, in some cases, evolve into debilitating overuse injuries and pain throughout the right upper limb. Altering the thumb-rest position has been proposed as a way to alleviate this discomfort, although no quantitative research has been conducted on this issue. The purpose of this study was to address the impact of thumb-rest position on the neuromuscular control of holding the clarinet. Surface electromyographic recordings of superficial muscles that control the right thumb, wrist, and arm were taken during realistic playing tasks. Twenty clarinetists performed 10 held notes and 10 exercises on the three different thumb-rest positions. The notes and exercises were chosen to isolate specific elements of playing. We hypothesized that a high thumb-rest position would result in a significantly different balance of muscle activity than traditional and low thumb-rest positions. The patterns of muscle activity recorded among clarinetists were idiosyncratic, but for all players these patterns were influenced by the note(s) played and thumb-rest position, and thus the hypothesis was partially supported. Muscles that acted on the thumb and wrist were most influenced by thumb-rest position. These results support the notion that adjustment of thumb-rest position may be a useful way to alleviate discomfort in the supporting limb but must be evaluated for each individual.

FMS: Relationship between muscul activity in deep squat ans trunk stability pushup

Aims and Objectives:Motor control is described as the internal control and regulation processes which facilitate movements. Scientists divide motor control into the function of stability and the movement to maintain balance in locomotion. The FMS is used to analyze the motor behavior of muscle slings on the one hand, and to estimate injury risk on the other hand. Yet, the true extent of the FMS’ diagnostic information remains unclear. The low intensity level of the FMS items causes low tension within the motor network. Based on Hennemen’s size principle, this is a clear indicator for the activation of slow-twitch fibers in the muscle. A possible relationship between movement and stability function of muscle slings has yet to be examined. Therefore, the aim of this investigation was to shed light on the motor behavior of dynamic and isometric muscle activity as well as the examination of average muscle activity when performing the items deep squat (DS) and trunk stability pushup (TSPU).Materials and Methods:Data from 16 collegiate athletes (22.1±1.5yrs) with various sports histories was analyzed. The data analysis was based on Kendall’s tau correlation coefficient. The items DS and TSPU were rated via an ordinal ranking system ranging from 0 (pain) to 3 (adequate). Muscle activity was recorded with a new EMG device at a rate of 25 Hz (Myontec Ltd, Kuopio, Finland). In a concurrent pilot study the reliability of this device was examined with a progressive loaded squat protocol (50 up to 125% BW). It indicated almost perfect reliability for the quad/ham balance, quadriceps distribution (r< 0.9, CV:3-5%) and high reliability for the hamstrings (r >0.8, CV:<10%).Results:Strong relationships between the quad/ham balance (r=0.7, p<0.01) and quadriceps distribution (r=0.6, p<0.03) in DS and TSPU were identified. The connection between hamstring muscle activity balance was low (r< 0.2, p>0.5). In both items, the muscle contractions were dominated by the activation of the quadriceps (79% vs. 21% hamstrings). Additionally, the average muscle activity was 4 times higher in a loaded squat (100% BW) than it was in DS. Generally, DS was rated as follows: score 3 (3 times) and score 2 (13 times). For the item TSPU score 3 was given 14 times and score 2 was given 2 times.Conclusion:The relationship between dynamic and static motor behavior of the quadriceps supports the connection between the stabilizing and movement function of muscle slings. The low intensity corresponds with the slow EMG activity in DS, which is an indicator for the activation of mainly slow twitch muscle fibers. This scientific innovation is relevant for practitioners as it establishes the diagnostic value of the FMS. Based on this evidence, the FMS provides information with regards to low tension motor behavior. It is unlikely that this information is specific enough to estimate injury risk or performance because when it comes to return to sport decisions, it is also important to obtain information of motor control associated with fast-twitch fibers.

Electromyography activity of selected trunk muscles during cardiopulmonary resuscitation

BackgroundUnderstanding trunk muscle activity during chest compression may improve cardiopulmonary resuscitation (CPR) training strategies of CPR or prevent low back pain. This study investigates the trunk muscle activity pattern of chest compression in health care providers to determine the pattern alternation during chest compression. MethodsThirty-one experienced health care providers performed CPR for 5 minutes at a frequency of 100 compressions per minute. An electromyography (EMG) system was used to record muscle activity in the first minute, the third minute, and the fifth minute. Electrodes were placed bilaterally over the pectoralis major, latissimus dorsi, rectus abdominis, erector spinae, and gluteus maximus. We calculated the root mean square (RMS) value and maximal amplitude of the EMG activity, median frequency, and delivered force. ResultsThe maximal amplitude of EMG of the pectoralis major, erector spinae, and rectus abdominis showed large muscle activity above 45% of maximal voluntary contraction under chest compression. There were no significant differences in the RMS value of one chest compression cycle (RMS100%) and median frequency for all muscles at the first, third, and fifth minutes. Only gluteus maximus showed significant imbalance. The EMG ratios (erector spinae/rectus abdominis; erector spinae/gluteus maximus) increased significantly over time. The delivered force, compression depth, and number of correct depth decreased significantly over time. ConclusionWe suggest that the muscle power training for the pectoralis major, erector spinae, and rectus abdominis could be helpful for health care providers. Keeping muscle activity balance of bilateral gluteus maximus and maintaining the same level of EMG ratios might be the keys to prevent low back pain while performing CPR.

Kettlebell swing targets semitendinosus and supine leg curl targets biceps femoris: an EMG study with rehabilitation implications

BackgroundThe medial hamstring muscle has the potential to prevent excessive dynamic valgus and external rotation of the knee joint during sports. Thus, specific training targeting the medial hamstring muscle seems...

Heterogeneous activity level of jaw-closing and -opening muscles and its association with arousal levels during sleep in the guinea pig

Exaggerated jaw motor activities during sleep are associated with muscle symptoms in the jaw-closing rather than the jaw-opening muscles. The intrinsic activity of antagonistic jaw muscles during sleep remains unknown. This study aims to assess the balance of muscle activity between masseter (MA) and digastric (DG) muscles during sleep in guinea pigs. Electroencephalogram (EEG), electroocculogram, and electromyograms (EMGs) of dorsal neck, MA, and DG muscles were recorded with video during sleep-wake cycles. These variables were quantified for each 10-s epoch. The magnitude of muscle activity during sleep in relation to mean EMG activity of total wakefulness was up to three times higher for MA muscle than for DG muscle for nonrapid eye movement (NREM) and rapid-eye-movement (REM) sleep. Although the activity level of the two jaw muscles fluctuated during sleep, the ratio of activity level for each epoch was not proportional. Epochs with a high activity level for each muscle were associated with a decrease in deltaEEG power and/or an increase in heart rate in NREM sleep. However, this association with heart rate and activity levels was not observed in REM sleep. These results suggest that in guinea pigs, the magnitude of muscle activity for antagonistic jaw muscles is heterogeneously modulated during sleep, characterized by a high activity level in the jaw-closing muscle. Fluctuations in the activity are influenced by transient arousal levels in NREM sleep but, in REM sleep, the distinct controls may contribute to the fluctuation. The above intrinsic characteristics could underlie the exaggeration of jaw motor activities during sleep (e.g., sleep bruxism).