Synergistic Muscles Research Articles

Gender- and Muscle-Specific Responses During Fatiguing Exercise.

Hill, EC, Housh, TJ, Smith, CM, Schmidt, RJ, and Johnson, GO. Gender- and muscle-specific responses during fatiguing exercise. J Strength Cond Res 32(5): 1471-1478, 2018-The purpose of the present investigation was to examine potential gender-related differences in electromyographic (EMG) and mechanomyographic (MMG) responses during submaximal, concentric, isokinetic, forearm flexion muscle contractions. Twelve men and 12 women performed concentric peak torque trials before (pretest) and after (posttest) a fatiguing exercise bout that consisted of 50 submaximal (65% of concentric peak torque), concentric, isokinetic (60°·s), forearm flexion muscle contractions. Surface EMG and MMG signals were simultaneously recorded from the biceps brachii and brachioradialis muscles. There was a gender-related difference in the decline in absolute concentric peak torque for the men (23.8%) vs. women (18.5%) that was eliminated when covaried for differences in pretest concentric peak torque values. During the fatiguing exercise bout, EMG amplitude(AMP) increased and EMG mean power frequency (MPF) decreased for both genders and muscles. There were, however, muscle- and gender-specific increases, decreases, and no changes for MMG AMP and MMG MPF. The gender-related difference for the posttest decline in concentric peak torque was associated with differences in muscle strength which may have resulted in greater blood flow occlusion in the men than the women. The muscles with the most pronounced fatigue-induced neuromuscular responses were the biceps brachii in men and the brachioradialis in women. These findings may be related to gender differences in the usage patterns of synergistic muscles during a fatiguing task.

T80. Alteration of intermuscular coherence in synergistic muscle pairs during actual elbow flexion contractions after cervical spinal cord injury

Introduction During isometric contractions, the level of antagonist muscles activation is increased in people with cervical spinal cord injury (cSCI) in comparison to healthy participants. This alteration of antagonists activation after cSCI has been primarily associated with a lower cortical control of the spinal mechanisms – especially reciprocal inhibition – regulating agonists-antagonists co-activation. Through time-frequency intermuscular coherence analysis, which is likely to reflect the strength of the common neural drive across multiple muscles, this study investigates the influence of a cSCI on the common neural drive regulating the activity of agonist and antagonist muscles pairs. Methods The EMG of elbow flexors (biceps brachii, brachioradialis) and elbow extensors (long and short heads of the triceps brachii) was recorded while 8 participants with cSCI (SCI group) and 10 able-bodied participants (AB group) performed 21 isometric 6-s elbow isometric flexion contractions at 3 force levels (20%, 40% and 60% of MVC). The magnitude of intermuscular coherence between the EMG signals from elbow flexors (AGO-AGO), elbow extensors (ANTAGO-ANTAGO) and all possible pairs of elbow flexors-extensors (AGO-ANTAGO) was quantified in alpha (8–12 Hz), beta (15–30 Hz) and gamma (35–60 Hz) frequency bands. The magnitude of the intermuscular coherence and the mean net joint torque produced around the elbow joint were analyzed over a 2-s stable force production window for all contractions. The effects of the Force level and Group were tested using adequate statistical tests according to the distribution of the dependent variables. Results Results revealed that the net joint torque significantly increased with the Force level in both groups with no significant Group difference. In the beta-band, AGO-ANTAGO intermuscular coherence magnitude was significantly lower in the SCI group than in the AB group. In the gamma-band, the ANTAGO-ANTAGO intermuscular coherence magnitude significantly increased concomitantly with the Force level in both groups. No significant intermuscular coherence was found in the alpha-band, whatever the group and the muscle pair. Conclusion The alteration of AGO-ANTAGO intermuscular coherence magnitude in the beta-band after cSCI could reflect reduced common neural drive influencing the spinal inhibitory mechanisms. This finding may suggest lower common drive to agonist-antagonist muscle pairs in SCI participants, which could take part in the alteration of antagonist muscles co-activation. Increased ANTAGO-ANTAGO coherence magnitude with the force level revealed in the gamma-band could be related to the Piper rhythm phenomenon, which contributes to synchronize muscle activations to gain in efficiency, especially at high force levels. Despite lower intermuscular coupling between agonist and antagonist muscles, our results taken together support that the central mechanisms controlling the modulation of the force level are preserved during actual contractions after cSCI.

Hip and trunk muscles activity during nordic hamstring exercise.

The nordic hamstring exercise (NHE) is a dynamic lengthening hamstring exercise that requires trunk and hip muscles activation. Thigh muscles activation, specifically hamstring/quadriceps contractions has been previously examined during NHE. Trunk and hip muscles activity have not been enough studied. The aim of this study was to analyze of hip and trunk muscles activity during NHE. Surface electromyography (EMG) and kinematic data were collected during NHE. Ten healthy men with the age range of 21–36 years performed two sets of two repetitions with downward and upward motions each of NHE. EMG activity of fifteen trunk and hip muscles and knee kinematic data were collected. Muscle activity levels were calculated through repeated measure analysis of variance in downward and upward motions, through Paired t-test between downward and upward motions and gluteus maximus to erector spine activity ratio (Gmax/ES ratio) using Pearson correlation analyses were evaluated. Semitendinosus and biceps femoris muscles activity levels were the greatest in both motions and back extensors and internal oblique muscles activity were greater than other muscles (P<0.05). The decreased Gmax/ES ratio was significantly related to peak knee extension angle in downward (r=0.687) and upward motions (r=0.753) (P<0.05). These findings indicate the importance of synergistic muscles and trunk muscles coactivation in eccentric and concentric hamstrings contractions. It could be important for early assessment of subjects with hamstring injury risk.

Neck muscle biomechanics and neural control.

The mechanics, morphometry, and geometry of our joints, segments, and muscles are fundamental biomechanical properties intrinsic to human neural control. The goal of our study was to investigate whether the biomechanical actions of individual neck muscles predict their neural control. Specifically, we compared the moment direction and variability produced by electrical stimulation of a neck muscle (biomechanics) to the preferred activation direction and variability (neural control). Subjects sat upright with their head fixed to a six-axis load cell and their torso restrained. Indwelling wire electrodes were placed into the sternocleidomastoid (SCM), splenius capitis (SPL), and semispinalis capitis (SSC) muscles. The electrically stimulated direction was defined as the moment direction produced when a current (2-19 mA) was passed through each muscle's electrodes. Preferred activation direction was defined as the vector sum of the spatial tuning curve built from root mean squared electromyogram when subjects produced isometric moments at 7.5% and 15% of their maximum voluntary contraction (MVC) in 26 three-dimensional directions. The spatial tuning curves at 15% MVC were well defined (unimodal, P < 0.05), and their preferred directions were 23°, 39°, and 21° different from their electrically stimulated directions for the SCM, SPL, and SSC, respectively ( P < 0.05). Intrasubject variability was smaller in electrically stimulated moment directions compared with voluntary preferred directions, and intrasubject variability decreased with increased activation levels. Our findings show that the neural control of neck muscles is not based solely on optimizing individual muscle biomechanics but, as activation increases, biomechanical constraints in part dictate the activation of synergistic neck muscles. NEW & NOTEWORTHY Biomechanics are an intrinsic part of human neural control. In this study, we found that the biomechanics of individual neck muscles cannot fully predict their neural control. Consequently, physiologically based computational neck muscle controllers cannot calculate muscle activation schemes based on the isolated biomechanics of muscles. Furthermore, by measuring biomechanics we showed that the intrasubject variability of the neural control was lower for electrical vs. voluntary activation of the neck muscles.

Altered muscle synergies during gait in individuals with knee osteoarthritis

Purpose: While there are well documented differences in gait between symptomatic knee osteoarthritis (OA) as compared to healthy older adults the mechanism for how these altered movement patterns occur are not well characterized. Quantification of synergistic muscle activation patterns in knee OA may provide insight to the altered control of movement that may result from joint pain, inactivity, or changes in joint structure, and contribute to the decline in physical function. It has been proposed that movement may be controlled through synergistic activation of muscle groups working as a single functional unit. Quantification of these groupings (aka muscle synergies) can provide insight into neural control of movement by describing not only which muscles are coactivating, but also how they work together to carry out functional movements. In both cerebral palsy and stroke, fewer synergies were needed to describe movements, compared to healthy or unaffected limbs, suggesting a simplified control pattern due to co-contraction. In addition, differences found in the make-up of the muscle synergies throughout movement tasks suggest less coordinated movement with more severe pathologies. The purpose of our study is to quantify differences in muscle synergies between individuals with symptomatic knee OA and healthy older adults. We hypothesize that due to cocontraction, there will be fewer muscle synergies in individuals with knee OA compared to healthy older adults, and that the contribution of these synergies will differ throughout the gait cycle. Methods: After IRB approval, 17 healthy older adults (HA) and 17 symptomatic knee OA were enrolled. Participants walked on a treadmill at a preferred pace and following a 2 minute warm-up EMG was collected at 2000 Hz on 8 leg muscles. EMG signals were then filtered, rectified, and normalized to the gait cycle for 9 total strides for each individual. Mean data for each individual was then concatenated to form one group matrix for OA and one for HA in order to account for individual characteristics within groups in synergy analysis. Muscle synergies were extracted using non-negative matrix factorization (NMF) in both HA and OA. Variance accounted for (VAF = 1-SSE/SSTE) was calculated to determine the number of synergies needed to describe >90% of variance in muscle activation and used to test for differences in complexity of movement between groups. Differences in the contribution of individual muscles to each synergy was determined via visual inspection and then the activation of similar synergies at 0, 30, and 66% of the gait cycle (approx. heel-strike(HS), peak knee flexion(pKF), and toe-off(TO) respectively) were compared using one-way ANOVA's. Results: To account for >90% variability, 4 synergies were needed in the OA group (VAF = 93.4%), while only 3 were needed in the HA group (VAF = 92.4%). In order to easily compare between groups 4 synergies were used to describe both OA and HA (VAF = 96.9%). At HS, activation of synergy C (Fig.1) for OA (0.10 ± 0.21) was significantly higher compared to HA (0.06 ± 0.04, P = 0.001). At pKF, activation of synergy B was significantly higher in OA (0.08 ± 0.04) compared to HA (0.05 ± 0.02, P = 0.010). No difference was found between activation of synergies at TO. Conclusions: In contrast to our hypothesis a greater number of synergies were needed to account for >90% variance in the EMG for the OA group compared to the HA group, suggesting that control patterns in OA are not less complex. The differences in the contributions of the VL, VM and MH to synergy B along with greater activations of synergies B and C at pKF and HS respectively in OA suggests in agreement with the hypothesis that there is greater co-activation of the quadriceps and hamstrings in gait. A strong synergistic relationship between the quadriceps and hamstrings in OA may be related to either pain or joint instability and warrants further analysis to understand the contributing factors.

Myomodulation with Injectable Fillers: An Innovative Approach to Addressing Facial Muscle Movement.

Consideration of facial muscle dynamics is underappreciated among clinicians who provide injectable filler treatment. Injectable fillers are customarily used to fill static wrinkles, folds, and localized areas of volume loss, whereas neuromodulators are used to address excessive muscle movement. However, a more comprehensive understanding of the role of muscle function in facial appearance, taking into account biomechanical concepts such as the balance of activity among synergistic and antagonistic muscle groups, is critical to restoring facial appearance to that of a typical youthful individual with facial esthetic treatments. Failure to fully understand the effects of loss of support (due to aging or congenital structural deficiency) on muscle stability and interaction can result in inadequate or inappropriate treatment, producing an unnatural appearance. This article outlines these concepts to provide an innovative framework for an understanding of the role of muscle movement on facial appearance and presents cases that illustrate how modulation of muscle movement with injectable fillers can address structural deficiencies, rebalance abnormal muscle activity, and restore facial appearance.Level of Evidence V This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Myomodulation with Injectable Fillers: An Innovative Approach to Addressing Facial Muscle Movement

Consideration of facial muscle dynamics is underappreciated among clinicians who provide injectable filler treatment. Injectable fillers are customarily used to fill static wrinkles, folds, and localized areas of volume loss, whereas neuromodulators are used to address excessive muscle movement. However, a more comprehensive understanding of the role of muscle function in facial appearance, taking into account biomechanical concepts such as the balance of activity among synergistic and antagonistic muscle groups, is critical to restoring facial appearance to that of a typical youthful individual with facial esthetic treatments. Failure to fully understand the effects of loss of support (due to aging or congenital structural deficiency) on muscle stability and interaction can result in inadequate or inappropriate treatment, producing an unnatural appearance. This article outlines these concepts to provide an innovative framework for an understanding of the role of muscle movement on facial appearance and presents cases that illustrate how modulation of muscle movement with injectable fillers can address structural deficiencies, rebalance abnormal muscle activity, and restore facial appearance.Level of Evidence VThis journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

Infrared Laser Improves Collagen Organization in Muscle and Tendon Tissue During the Process of Compensatory Overload.

The photobiomodulation using the low-level laser therapy (LLLT) exerts a positive modulating effect on the synthesis of collagen in skeletal muscles and tendons. However, few studies have addressed this effect during the compensatory overload. Evaluate the effect of infrared laser on the deposition and organization of collagen fibers in muscle and tendon tissue during compensatory overload of the plantar muscle in rats. Wistar rats were submitted to bilateral ablation of the synergist muscles of the hind paws and divided in groups: Control, Hypertrophy, and Hypertrophy (H)+LLLT (780 nm, 40 mW, 9.6 J/cm2 and 10 s/point, 8 points, total energy 3.2 J, daily), evaluated at 7 and 14 days. Muscle cuts were stained with Picrosirius-Red and hematoxylin-eosin and tendon cuts were submitted to birefringence for determination of collagen distribution and organization. After 7 days an increase was observed in the area between beam muscles in H+LLLT (25.45% ± 2.56) in comparison to H (20.3% ± 3.31), in mature fibers and fibrilis in H+LLLT (29346.88 μm2 ± 2182.56; 47602.8 μm2 ± 2201.86 respectively) in comparison to H (26656.5 μm2 ± 1880.46; 45630.34 μm2 ± 2805.82 respectively) and in the collagen area in H+LLLT (2.25% ± 0.19) in comparison to H (2.0% ± 0.15). However, after 14 days a reduction was observed in the area between beam muscles in H+LLLT (13.88% ± 2.54) in comparison to H (19.1% ± 2.61), in fibrils and mature fibers in H+LLLT (17174.1 μm2 ± 2563.82; 32634.04 μm2 ± 1689.38 respectively) in comparison to H (55249.86 μm2 ± 1992.65; 44318.36 μm2 ± 1759.57) and in the collagen area in H+LLLT (1.76% ± 0.16) in comparison to H (2.09 ± 0.27). A greater organization of collagen fibers in the tendon was observed after 7 and 14 days in H+LLLT groups. Infrared laser irradiation induces an improvement in collagen organization in tendons and a reduction in the total area of collagen in muscles during compensatory atrophy following the ablation of synergist muscles.

Surface electromyographic amplitude does not identify differences in neural drive to synergistic muscles.

Surface electromyographic (EMG) signal amplitude is typically used to compare the neural drive to muscles. We experimentally investigated this association by studying the motor unit (MU) behavior and action potentials in the vastus medialis (VM) and vastus lateralis (VL) muscles. Eighteen participants performed isometric knee extensions at four target torques [10, 30, 50, and 70% of the maximum torque (MVC)] while high-density EMG signals were recorded from the VM and VL. The absolute EMG amplitude was greater for VM than VL ( P < 0.001), whereas the EMG amplitude normalized with respect to MVC was greater for VL than VM ( P < 0.04). Because differences in EMG amplitude can be due to both differences in the neural drive and in the size of the MU action potentials, we indirectly inferred the neural drives received by the two muscles by estimating the synaptic inputs received by the corresponding motor neuron pools. For this purpose, we analyzed the increase in discharge rate from recruitment to target torque for motor units matched by recruitment threshold in the two muscles. This analysis indicated that the two muscles received similar levels of neural drive. Nonetheless, the size of the MU action potentials was greater for VM than VL ( P < 0.001), and this difference explained most of the differences in EMG amplitude between the two muscles (~63% of explained variance). These results indicate that EMG amplitude, even following normalization, does not reflect the neural drive to synergistic muscles. Moreover, absolute EMG amplitude is mainly explained by the size of MU action potentials. NEW & NOTEWORTHY Electromyographic (EMG) amplitude is widely used to compare indirectly the strength of neural drive received by synergistic muscles. However, there are no studies validating this approach with motor unit data. Here, we compared between-muscles differences in surface EMG amplitude and motor unit behavior. The results clarify the limitations of surface EMG to interpret differences in neural drive between muscles.

Differing structural properties of foods affect the development of mandibular control and muscle coordination in infants and young children

The development of chewing is an essential motor skill that is continually refined throughout early childhood. From a motor control perspective, the advancement of textures is dependent upon the fit between a child's oral anatomic and motor system and food properties. The purpose of this exploratory study is to identify age-related changes in chewing motor coordination and control and to determine if these changes are associated with the differing structural properties of solid foods, as well as to explore the role of explanatory variables such as the emergence of teeth and bite force. The masticatory muscle coordination (i.e., coupling of synergistic and antagonistic muscle pairs) and control (i.e., speed, displacement, chewing rate, duration, and number of chews) of fifty children were assessed cross-sectionally at five ages: 9-, 12-, 18-, 24-, and 36-months using electromyography (EMG) and 3D optical motion capture while children ate three foods that had differing structural properties. The results of this study found that children made gains in their chewing motor control (decreased duration of chewing sequences and lateral jaw displacement) and coordination (improved jaw muscle coupling) throughout this period. The structural differences in foods also affected chewing performance at all ages. These preliminary findings suggest that some solid textures are better adapted for immature mandibular control than others and that the development of chewing is a protracted process that may be impacted by the emergence of teeth and changes to bite force.

Mechanical Coupling Between Muscle-Tendon Units Reduces Peak Stresses.

The presence of mechanical linkages between synergistic muscles and their common tendons may distribute forces among the involved structures. We review studies, using humans and other animals, examining muscle and tendon interactions and discuss the hypothesis that connections between muscle bellies and within tendons may serve as a mechanism to distribute forces and mitigate peak stresses.

Correlation between diaphragm thickness and respiratory synergist muscle activity according to severity of chronic obstructive pulmonary disease.

[Purpose] This study aims to analyze the effect that moderate to severe chronic obstructive pulmonary disease (COPD) has on the respiratory synergist muscles. The results will provide basic data that can be used in the clinical management of COPD. [Subjects and Methods] The subjects in the study were 47 male patients with COPD between 55 and 70 years old who were treated in a medical institution located in Jeollanam-do Province, South Korea, from October 2015 to December 2016. Measurements were analyzed to determine the correlation between the diaphragm thickness and the respiratory synergist muscle activity in patients with mild COPD. [Results] The results showed that there was a negative correlation between the diaphragm thickness and the sternocleidomastoid muscle and between the diaphragm thickness and the scalene muscle; however, there was a positive correlation between the diaphragm thickness and the external intercostal. For patients with severe COPD, negative correlations were found between the diaphragm thickness and the sternocleidomastoid muscle and between the diaphragm thickness and the scalene muscle. [Conclusion] The mechanical deformation of the thoracic cage caused by severe COPD reduces the lung capacity of patients and, thus, increases the difficulty in breathing. As the disease worsens, the patients tend to maintain ventilation using the respiratory synergist muscles. Thus, offering early and aggressive treatment and a respiration rehabilitation program to patients with COPD can help to reduce the actions of the respiratory synergist muscles to ensure normal breathing.

Neuromechanical coupling within the human triceps surae and its consequence on individual force-sharing strategies.

Little is known about the factors that influence the coordination of synergist muscles that act across the same joint, even during single-joint isometric tasks. The overall aim of this study was to determine the nature of the relationship between the distribution of activation and the distribution of force-generating capacity among the three heads of the triceps surae [soleus (SOL), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL)]. Twenty volunteers performed isometric plantarflexions, during which the activation of GM, GL and SOL was estimated using electromyography (EMG). Functional muscle physiological cross-sectional area (PCSA) was estimated using imaging techniques and was considered as an index of muscle force-generating capacity. The distribution of activation and PCSA among the three muscles varied greatly between participants. A significant positive correlation between the distribution of activation and the distribution of PCSA was observed when considering the two bi-articular muscles at intensities ≤50% of the maximal contraction (0.51<r<0.62). Specifically, the greater the PCSA of GM compared with GL, the stronger bias of activation to the GM. There was no significant correlation between monoarticular and biarticular muscles. A higher contribution of GM activation compared with GL activation was associated with lower triceps surae activation (-0.66<r<-0.42) and metabolic cost (-0.74<r<-0.52) for intensities ≥30% of the maximal contraction. Considered together, an imbalance of force between the three heads was observed, the magnitude of which varied greatly between participants. The origin and consequences of these individual force-sharing strategies remain to be determined.

Correlation between pulmonary functions and respiratory muscle activity in patients with forward head posture.

[Purpose] The purpose of this study is to determine the effect that secondary postural deformities and chronic postural abnormalities have on lung capacity, as well as correlate the activity of the respiratory muscles. The results provide basic objective data about the forward head posture and respiratory muscle activity that can be used in clinical situations. [Subjects and Methods] The subjects used in this study were 24 patients aged 25 to 35 years old who visited a hospital in Jeollanam-do Province, Korea, between September 2015 and January 2016. The patients were diagnosed with forward head posture because the vertical line between the acromion process and the external acoustic meatus was at least 5 cm. We measured the craniovertebral angle, pulmonary functions, and respiratory muscle activity of the subjects for correlation analysis. [Results] A positive correlation was found between the craniovertebral angle and the forced vital capacity (r=0.63), while a negative correlation was found between the craniovertebral angle and the sternocleidomastoid muscle (r=–0.77). The craniovertebral angle and the anterior scalene muscle showed a negative correlation (r=–0.65). There were positive correlations between the forced vital capacity and the sternocleidomastoid muscle (r=0.71), and between the forced vital capacity and the anterior scalene muscle (r=0.59). [Conclusion] Severe forward head posture increased the activities of the sternocleidomastoid muscles and the anterior scalene muscles, and decreased the forced vital capacity. Thus, it is necessary to develop more efficient interventions for managing forward head posture based on pulmonary function and the activity of the respiratory synergist muscles.

Effects of antagonistic and synergistic muscles’ co-activation on mechanics of activated spastic semitendinosus in children with cerebral palsy

ObjectivesMost activities involve co-activation of several muscles and epimuscular myofascial force transmission (EMFT) can affect their mechanics. This can be relevant for spastic muscles of cerebral palsy (CP) patients. Isometric spastic semitendinosus (ST) forces vs. knee angle (KA-FST) data were collected intra-operatively to test the following hypotheses: (i) Inter-antagonistic EMFT elevates FST, (ii) changes the shape of KA-FST characteristics, (iii) reduces the muscle’s joint range of force exertion (Range-FST) and (iv) combined inter-antagonistic and synergistic EMFT further changes those effects. Methods11 limbs of 6 patients with CP (mean (SD) = 7.7 (4.7) years; GMFCS levels = II–IV) were tested in 3 conditions from 120° to full extension: ST activated (I) exclusively, (II) simultaneously with an antagonist, and (III) with added activation of synergists. ResultsCondition II increased FST (e.g., peak force = 87.6 N (30.5 N)) significantly (by 33.6%), but condition III caused no further change. No condition changed the muscle’s wide Range-FST (100.7° (15.9°)) significantly. Therefore, only the first hypothesis was confirmed. ConclusionsCo-activating its antagonist elevates forces of activated spastic ST substantially, but does not change its joint range of force exertion. Added activation of its synergists causes no further effects. Therefore, EMFT effects in CP can be relevant and need to be tested in other knee flexors.

Функциональные нарушения мышечного тонуса и их коррекция методом динамической мышечно-фасциальной мобилизации у спортсменов

Objective: efficacy evaluation of the method of dynamic musculofascial mobilization for restoration of myostatic reflex in athletes and sport veterans with musculofascial pain syndrome. Materials and Methods: 60 athletes and sport veterans aged from 20 to 50 years old with functional disorders of muscle tone, accompanied by myofascial pain syndrome and deformations of the contours of the body participated in the study. Questionnaires and examination scales clinically appropriated in neurology were used to assess the degree of clinical disorders. We examined and treated 36 patients with signs of humeroscapular periarthrosis, epicondylitis of the elbow, gonarthrosis and coxarthrosis of the 1-2 stage and 24 patients with vertebrogenic radicular neural symptoms. All patients were treated by dynamic musculofascial mobilization (DMFM) by deep mechanical effect on muscles and the fascial intermuscular septums during active contraction of patient’s agonistic and synergistic muscles. Results: 52 patients had complete recovery of physical activity with restoration of myostatic reflex of all muscle groups. 8 patients had the satisfactory result of treatment. Approximately half of treated patients during the 2 nd session had recovery of muscle tone of all previously identified hypotonic muscles. Conclusions: application of DMFM promotes active restoration of the myostatic reflex, reduction in the number of treatment sessions and their duration. The method of exposure is maximally simplified and can be performed by a specially trained nursing staff in terms of sports competitions.

Motor module activation sequence and topography in the spinal cord during air‐stepping in human: Insights into the traveling wave in spinal locomotor circuits

Coordinated locomotor muscle activity is generated by the spinal central pattern generators (CPGs), which are modulated by peripheral and supraspinal inputs. The CPGs would consist of multiple motor modules generating basic muscle activity, which are distributed rostrocaudally along the spinal cord. To activate the motor modules in proper sequence, rostrocaudally traveling waves of activation in the spinal cord are important mechanisms in the CPGs. The traveling waves of activation have been observed in nonhuman vertebrates. However, they have not yet been confirmed during human locomotion. Although, rostrocaudal wave‐like activations in the spinal cord were observed during walking in humans in a previous study, the propagation shifted rostrally toward the upper lumbar segments at foot contact. Here, using an air stepping task to remove the foot‐contact interactions, we examined whether the traveling wave mechanism exists in the human spinal circuits based on the activation sequence of motor modules and their topography. We measured electromyographic activity of lower leg muscles during the air‐stepping task. Then, we extracted motor modules (i.e., basic patterns of sets of muscle activations: muscle synergies) from the measured muscle activities using nonnegative matrix factorization method. Next, we reconstructed motoneuron (MN) activity from each module activity based on myotomal charts. We identified four types of motor modules from muscle activities during the air‐stepping task. Each motor module represented different sets of synergistic muscle activations. MN clusters innervating each motor module were sequentially activated from the rostral to caudal region in the spinal cord, from the initial flexion to the last extension phase during air‐stepping. The rostrocaudally sequential activation of MN clusters suggests the possibility that rostrocaudally traveling waves exist in human locomotor spinal circuits. The present results advance the understanding of human locomotor control mechanisms, and provide important insights into the evolution of locomotor networks in vertebrates.

Architectural Properties of Sloth Forelimb Muscles (Pilosa: Bradypodidae)

Tree sloths have reduced skeletal muscle mass, and yet they are able to perform suspensory behaviors that require both strength and fatigue resistance to suspend their body mass for extended periods of time. The muscle architecture of sloths is hypothesized to be modified in ways that will enhance force production to compensate for this reduction in limb muscle mass. Our objective is to test this hypothesis by quantifying architecture properties in the forelimb musculature of the brown-throated three-toed sloth (Bradypus variegatus: N = 4). We evaluated architecture from 52 forelimb muscles by measuring muscle moment arm (r m), muscle mass (MM), belly length (ML), fascicle length (LF), pennation angle (θ), and physiological cross-sectional area (PCSA), and these metrics were used to estimate isometric force, joint torque, and power. Overall, the musculature becomes progressively more pennate from the extrinsic to intrinsic regions of the forelimb, and the flexors are more well developed than the extensors as predicted. However, most muscles are indicative of a mechanical design for fast joint rotational velocity instead of large joint torque (i.e., strength), although certain large, parallel-fibered shoulder (e.g., m. latissimus dorsi) and elbow (e.g., m. brachioradialis) flexors are capable of producing appreciable torques by having elongated moment arms. This type of functional tradeoff between joint rotational velocity and mechanical advantage is further exemplified by muscle gearing in Bradypus that pairs synergistic muscles with opposing LF/r m ratios in each functional group. These properties are suggested to facilitate the slow, controlled movements in sloths. In addition, the carpal/digital flexors have variable architectural properties, but their collective PCSA and joint torque indicates the capability for maintaining grip force and carpal stability while distributing load from the manus to the shoulder. The observed specializations provide a basis for understanding sustained suspension in sloths.

Muscle Shear Moduli Changes and Frequency of Alternate Muscle Activity of Plantar Flexor Synergists Induced by Prolonged Low-Level Contraction.

During prolonged low-level contractions, synergist muscles are activated in an alternating pattern of activity and silence called as alternate muscle activity. Resting muscle stiffness is considered to increase due to muscle fatigue. Thus, we investigated whether the difference in the extent of fatigue of each plantar flexor synergist corresponded to the difference in the frequency of alternate muscle activity between the synergists using muscle shear modulus as an index of muscle stiffness. Nineteen young men voluntarily participated in this study. The shear moduli of the resting medial and lateral gastrocnemius muscles (MG and LG) and soleus muscle (SOL) were measured using shear wave ultrasound elastography before and after a 1-h sustained contraction at 10% peak torque during maximal voluntary contraction of isometric plantar flexion. One subject did not accomplish the task and the alternate muscle activity for MG was not found in 2 subjects; therefore, data for 16 subjects were used for further analyses. The magnitude of muscle activation during the fatiguing task was similar in MG and SOL. The percent change in shear modulus before and after the fatiguing task (MG: 16.7 ± 12.0%, SOL: −4.1 ± 13.9%; mean ± standard deviation) and the alternate muscle activity during the fatiguing task (MG: 33 [20–51] times, SOL: 30 [17–36] times; median [25th–75th percentile]) were significantly higher in MG than in SOL. The contraction-induced change in shear modulus (7.4 ± 20.3%) and the alternate muscle activity (37 [20–45] times) of LG with the lowest magnitude of muscle activation during the fatiguing task among the plantar flexors were not significantly different from those of the other muscles. These results suggest that the degree of increase in muscle shear modulus induced by prolonged contraction corresponds to the frequency of alternate muscle activity between MG and SOL during prolonged contraction. Thus, it is likely that, compared with SOL, the alternate muscle activity of MG occurs more frequently during prolonged contraction due to the greater increase in fatigue of MG induced by the progression of a fatiguing task.

"Discrete peaks" of excitability and map overlap reveal task-specific organization of primary motor cortex for control of human forearm muscles.

The primary motor cortex (M1) presents a somatotopic organization of body parts, but with overlap between muscle/movement representations. This distinct but overlapping M1 organization is believed to be important for individuated control and movement coordination, respectively. Discrete peaks of greater excitability observed within M1 might underpin organization of cortical motor control. This study aimed to examine interactions between M1 representations of synergist and antagonist forearm muscles, compare regions of greater excitability during different functional tasks, and compare characteristics of M1 representation recorded using surface and fine-wire (fw ) electrodes. Transcranial magnetic stimulation (TMS) was applied over M1 for mapping the representation of 4 forearm muscles (extensor carpi radialis brevis [ECRB], extensor digitorum communis, flexor carpi radialis, and flexor digitorum superficialis) during three tasks: rest, grip, and wrist extension in 14 participants. There are three main findings. First, discrete areas of peak excitability within the M1 representation of ECRBfw were identified during grip and wrist extension suggesting that different M1 areas are involved in different motor functions. Second, M1 representations of synergist muscles presented with greater overlap of M1 representations than muscles with mainly antagonist actions, which suggests a role in muscle coordination. Third, as larger normalized map volume and overlap were observed using surface than fine-wire electrodes, data suggest that cross-talk from adjacent muscles compromised interpretation of recordings made with surface electrodes in response to TMS. These results provide a novel understanding of the spatial organization of M1 with evidence of "functional somatotopy." This has important implications for cortical control of movement. Hum Brain Mapp 38:6118-6132, 2017. © 2017 Wiley Periodicals, Inc.