Muscle Activation Patterns Research Articles

The effect of bolus properties on muscle activation patterns and TMJ loading during unilateral chewing

Mastication is a vital human function and uses an intricate coordination of muscle activation to break down food. Collection of detailed muscle activation patterns is complex and commonly only masseter and anterior temporalis muscle activation are recorded. Chewing is the orofacial task with the highest muscle forces, potentially leading to high temporomandibular joint (TMJ) loading. Increased TMJ loading is often associated with the onset and progression of temporomandibular disorders (TMD). Hence, studying TMJ mechanical stress during mastication is a central task. Current TMD self-management guidelines suggest eating small and soft pieces of food, but patient safety concerns inhibit in vivo investigations of TMJ biomechanics and currently no in silico model of muscle recruitment and TMJ biomechanics during chewing exists. For this purpose, we have developed a state-of-the-art in silico model, combining rigid body bones, finite element TMJ discs and line actuator muscles. To solve the problems regarding muscle activation measurement, we used a forward dynamics tracking approach, optimizing muscle activations driven by mandibular motion. We include a total of 256 different combinations of food bolus size, stiffness and position in our study and report kinematics, muscle activation patterns and TMJ disc von Mises stress. Computed mandibular kinematics agree well with previous measurements. The computed muscle activation pattern stayed stable over all simulations, with changes to the magnitude relative to stiffness and size of the bolus. Our biomedical simulation results agree with the clinical guidelines regarding bolus modifications as smaller and softer food boluses lead to less TMJ loading. The computed mechanical stress results help to strengthen the confidence in TMD self-management recommendations of eating soft and small pieces of food to reduce TMJ pain.

Masticatory Muscles Activation and TMJ Space During Asymmetrically Loaded Jaw Closing

Masticatory muscle activation and temporomandibular joint (TMJ) load generated during asymmetrically loaded jaw closing are largely unknown. Two different strategies were developed to explain how the central nervous system (CNS) generates muscle activation patterns during motion: minimization of joint load (MJL) vs. minimization of muscle effort (MME). The aim of the present study was to investigate, experimentally, the neuromuscular strategy selected by the CNS to coordinate jaw closing in reaction to the application of an external asymmetric load. Masticatory muscle activation was measured with electromyography (EMG) and the minimum intra-articular distance (MID) was assessed by dynamic stereometry to infer joint loading. Ten healthy subjects performed jaw-closing movements against an asymmetric mandibular load set from 0.0 to 2.0 kg in 0.5-kg steps. Recordings were analyzed by exploratory and graphical statistical tools. Moreover, the observed differences in MID and EMG among the various mandibular loads were tested using non-parametric tests for repeated measures data. The ipsilateral-contralateral differences in MID and EMG of the anterior temporalis showed a significant increase (p < 0.001, p = 0.01) with increasing asymmetrical load with both joints being most heavily loaded at 1 kg. EMG signals of the masseter did not change significantly with increasing load. This study is the first to have analyzed the changes in the TMJ intra-articular space during asymmetrically loaded jaw-closing movements, not only three dimensionally and dynamically, but also combined with EMG. Asymmetrical load affected the TMJ space and masticatory muscle activation patterns, primarily resulting in an increased activation of the anterior temporalis muscle. This might suggest the involvement of a control mechanism to protect the joints from overloading. However, the results do not fully support the hypothesis of MJL nor the MME strategy.

Sensorimotor adaptation of locomotor synergies to gravitational constraint

This study investigates the impact of gravity on lower limb muscle coordination during pedaling. It explores how pedaling behaviors, kinematics, and muscle activation patterns dynamically adapts to changes in gravity and resistance levels. The experiment was conducted in parabolic flights, simulating microgravity, hypergravity (1.8 g), and normogravity conditions. Participants pedaled on an ergometer with varying resistances. The goal was to identify potential changes in muscle synergies and activation strategies under different gravitational contexts. Results indicate that pedaling cadence adjusted naturally in response to both gravity and resistance changes. Cadence increased with higher gravity and decreased with higher resistance levels. Muscular activities were characterized by two synergies representing pull and push phases of pedaling. The timing of synergy activation was influenced by gravity, with a delay in activation observed in microgravity compared to other conditions. Despite these changes, the velocity profile of pedaling remained stable across gravity conditions. The findings strongly suggest that the CNS dynamically manages the shift in body weight by finely tuning muscular coordination, thereby ensuring the maintenance of a stable motor output. Furthermore, electromyography analysis suggest that neuromuscular discharge frequencies were not affected by gravity changes. This implies that the types of muscle fibers recruited during exercise in modified gravity are similar to those used in normogravity. This research has contributed to a better understanding of how the human locomotor system responds to varying gravitational conditions, shedding light on the potential mechanisms underlying astronauts’ gait changes upon returning from space missions.

Development and validation of a novel ankle joint musculoskeletal model.

An improved understanding of contact mechanics in the ankle joint is paramount for implant design and ankle disorder treatment. However, existing models generally simplify the ankle joint as a revolute joint that cannot predict contact characteristics. The current study aimed to develop a novel musculoskeletal ankle joint model that can predict contact in the ankle joint, together with muscle and joint reaction forces. We modelled the ankle joint as a multi-axial joint and simulated contact mechanics between the tibia, fibula and talus bones in OpenSim. The developed model was validated with results from experimental studies through passive stiffness and contact. Through this, we found a similar ankle moment-rotation relationship and contact pattern between our study and experimental studies. Next, the musculoskeletal ankle joint model was incorporated into a lower body model to simulate gait. The ankle joint contact characteristics, kinematics, and muscle forces were predicted and compared to the literature. Our results revealed a comparable peak contact force and the same muscle activation patterns in four major muscles. Good agreement was also found in ankle dorsi/plantar-flexion and inversion/eversion. Thus, the developed model was able to accurately model the ankle joint and can be used to predict contact characteristics in gait.

Teres minor deficiency does not predict clinically inferior external rotation after reverse total shoulder arthroplasty: a 2-year matched cohort study

BackgroundCurrent teaching maintains that reverse total shoulder arthroplasty (RTSA) is unlikely to restore external rotation (ER) without a functional posterior rotator cuff, specifically the teres minor (TM). This study compared restoration of ER in TM-deficient (TMD) with TM-intact (TMI) shoulders after RTSA. MethodsAll patients who underwent lateralized RTSA using an onlay prosthesis with no adjunct tendon transfers between January 2014 and July 2020 and with 2-year follow-up were identified. Preoperative imaging review identified patients with TMD, and propensity score matching was used to create a control group of equal size. TMD was divided into three subgroups: 1) atrophy; 2) fracture/malunion/nonunion (proximal humerus); and 3) endoprosthesis. Primary outcome measures were active ER range of motion (ROM) measured at the side, ΔER ROM from baseline, ER strength, and American Shoulder and Elbow Surgeons subscore question, “can you reach back of head.” ResultsThirty-nine patients with TMD shoulders (atrophy: n = 15; fracture n = 14; endoprosthesis: n = 10) were matched with 39 patients with TMI shoulders. Although TMD was associated with reduced baseline ER ROM (13.6 vs. 28.8; P = .004), the TMD group achieved greater ΔER ROM 2 years after RTSA (24.6 vs. 10.3; P = .014) and demonstrated comparable 2-year ER ROM (38.6 vs. 40.7; P = .484). The TMD group had a higher rate of ER weakness (12% vs. 0%; P = .044) but no difference in ability to reach back of head (unable: 24% vs. 20%; P = .686) or patient-reported functional scores (2-year American Shoulder and Elbow Surgeons: 76.2 vs. 74.8; P = .793). ConclusionThis study suggests that patients with an insufficient or absent teres minor can achieve satisfactory ER ROM and function after lateralized RTSA similar to their TMI peers. Future study will seek to identify muscle activation patterns of the shoulder girdle that allow TMD patients to overcome this insufficiency to perform activities requiring ER.

Intermuscular coherence reveals that affective emotional pictures modulate neural control mechanisms during the initiation of arm pointing movements.

Several studies in psychology provided compelling evidence that emotions significantly impact motor control. Yet, these evidences mostly rely on behavioral investigations, whereas the underlying neurophysiological processes remain poorly understood. Using a classical paradigm in motor control, we tested the impact of affective pictures associated with positive, negative or neutral valence on the kinematics and patterns of muscle activations of arm pointing movements performed from a standing position. The hand reaction and movement times were measured and electromyography (EMG) was used to measure the activities from 10 arm, leg and trunk muscles that are involved in the postural maintenance and arm displacement in pointing movements. Intermuscular coherence (IMC) between pairs of muscles was computed to measure changes in patterns of muscle activations related to the emotional stimuli. The hand movement time increased when an emotional picture perceived as unpleasant was presented as compared to when the emotional picture was perceived as pleasant. When an unpleasant emotional picture was presented, beta (β, 15-35 Hz) and gamma (γ, 35-60 Hz) IMC decreased in the recorded pairs of postural muscles during the initiation of pointing movements. Moreover, a linear relationship between the magnitude of the intermuscular coherence in the pairs of posturo-focal muscles and the hand movement time was found in the unpleasant scenarios. These findings reveal that emotional stimuli can significantly affect the content of the motor command sent by the central nervous system to muscles when performing voluntary goal-directed movements.

Electromyography of paraspinal muscles during self-corrective positions in adolescent idiopathic scoliosis.

Self-corrective exercise is commonly used in the training protocol of patients with adolescent idiopathic scoliosis (AIS). The muscle activation pattern during symmetrical and overcorrection exercises is then explored to guide the treatment. To compare the paraspinal muscle activity during three self-corrective positions and the habitual standing in AIS. Thirty-three adolescents with double curved scoliosis were examined. The curve type and Cobb's angle were determined from their whole spine X-ray. They adopted habitual standing, symmetrical correction and two overcorrected positions (O1 and O2). The surface electromyography (EMG) was monitored on both sides of paraspinal muscles at the apex areas of scoliotic curves. The EMG ratio between sides was inferred as the corrective effect. All three self-correction positions produced greater EMG ratios compared with the habitual standing. The greatest EMG ratios were observed during the O1 position at the thoracic curve and the habitual standing at the lumbar curve. Participants with different subtypes of curves exhibited similar patterns of EMG ratios. From the biomechanical viewpoint, all three self-corrective positions possibly provided therapeutic effects for the scoliotic body regardless of the subtype of scoliosis curves. The O1 position seemed to be most effective for the adjusting activation of thoracic paraspinal muscles. The symmetrical corrective position is otherwise recommended for adjusting the lumbar muscle activation.

A new methodological approach to characterize selective motor control in children with cerebral palsy.

Despite being a primary impairment in individuals with cerebral palsy (CP), selective motor control (SMC) is not routinely measured. Personalized treatment approaches in CP will be unattainable without the ability to precisely characterize the types and degrees of impairments in motor control. The objective of this study is to report the development and feasibility of a new methodological approach measuring muscle activation patterns during single-joint tasks to characterize obligatory muscle co-activation patterns that may underly impaired SMC. Muscle activation patterns were recorded during sub-maximal voluntary isometric contraction (sub-MVIC) tasks at the hip, knee, and ankle with an interactive feedback game to standardize effort across participants. We calculated indices of co-activation, synergistic movement, mirror movement, and overflow (indices range 0-2, greater scores equal to greater impairment in SMC) for each isolated joint task in 15 children - 8 with typical development (TD) (mean age 4.7 ± 1.0 SD years) and 7 with CP (mean age 5.8 ± 0.7 SD years). Indices were compared with Mann-Whitney tests. The relationships between the indices and gross motor function (GMFM-66) were examined with Pearson's r. Mean indices were higher in the CP vs. the TD group for each of the six tasks, with mean differences ranging from 0.05 (abduction and plantarflexion) to 0.44 (dorsiflexion). There was great inter-subject variability in the CP group such that significant group differences were detected for knee flexion mirroring (p = 0.029), dorsiflexion coactivation (p = 0.021), and dorsiflexion overflow (p = 0.014). Significant negative linear relations to gross motor function were found in all four indices for knee extension (r = -0.56 to -0.75), three of the indices for ankle dorsiflexion (r = -0.68 to -0.78) and in two of the indices for knee flexion (r = -0.66 to -0.67), and ankle plantarflexion (r = -0.53 to -0.60). Indices of coactivation, mirror movement, synergy, and overflow during single-joint lower limb tasks may quantify the type and degree of impairment in SMC. Preliminary concurrent validity between several of the indices of SMC and gross motor function was observed. Our findings established the feasibility of a new methodological approach that quantifies muscle activation patterns using electromyography paired with biofeedback during single-joint movement.

Pushing forward: exploring the impact of the sitting position on muscle activation patterns and force generation during paralympic sit-cross-country skiing.

Paralympic cross-country sit-skiing is a discipline of the Paralympic Winter Games where athletes use a specialized sledge. Athletes are classified into different groups according to their functional abilities. The double poling technique is used to push the sledge forward and generate speed. Different sitting positions in the sledge are used based on the individual impairment. To date there is no data available on the effects of these different positions on muscle activation patterns. The aim of this study was to analyze the muscle activation patterns of the trunk and upper body muscles in relation to the poling force. Nine Able-bodied athletes were tested on a treadmill at submaximal speed in three sitting positions for 4 min in a flat and uphill condition. Sitting positions included a "knee-high" position, a "knee-low" position, and a "neutral" position with the sitting platform parallel to the ground. Unilateral pole forces and surface EMG from three trunk muscles, two upper limb muscles, and one lower limb muscle were recorded simultaneously on the dominate side. Data were segmented into individual cycles and mean values and standard deviations calculated for each subject and condition. Statistical analyses, including a Friedman test and Bonferroni correction, were applied to examine significant differences across different sitting positions. Our findings demonstrate that while certain muscle groups such as the erector spinae and triceps show consistent patterns of activation across different sitting positions, there is considerable variability among individual athletes, suggesting individualized strategies for task execution. Overall, force application was most efficient in the "knee low" position with 691.33 ± 148.83 N and least efficient in the "knee high" position with 582.81 ± 115.11 N. Testing impaired athletes will be the next step in understanding the neurophysiological aspects of the poling movement. This experimental protocol provides a basis for understanding the movement of paralympic cross-country sit-skiing in greater depth.

Effect of Corrective Exercises on Posture, Upper Extremity Muscle Activity, and Shoulder Kinematics in Male Handball Players With Upper Cross Syndrome

Background and Aims Abnormal posture and alterations in movement and muscle activity patterns have been reported in people with upper cross syndrome (UCS). These changes can lead to imbalance in muscle activation, altered movement patterns, and biomechanical changes. The present study aims to investigate the effect of corrective exercises on posture, upper extremity muscle activity, and shoulder kinematics in male handball players with UCS. Methods This quasi-experimental study was conducted on 30 male handball players with UCS who were randomly divided into exercise (n=15) and control (n=15) groups. The variables including upper extremity muscle activation patterns, shoulder kinematics, forward head posture, forward shoulder posture, and kyphosis were evaluated before and after intervention. Should kinematics and activation patterns of upper extremity muscles (supraspinatus, lumbar erector spinae, upper trapezius, middle trapezius, latissimus dorsi, pectoralis major) were recorded using electromyography and motion analyzer. The angles of forward head and forward shoulder were assessed using photographic method taken from lateral view, and Kyphosis angle was measured using a flexible ruler before and after exercises. The exercise group performed the comprehensive corrective exercises for 8 weeks (3 sessions per week), but the control group did not receive any intervention. To analyze the data, two-way analysis of variance and Bonferroni test were used. The significant level was set at 0.05. Results Forward head posture (P=0.001), forward shoulder posture (P=0.003), and kyphosis (P=0.002) showed significant improvements in the exercise group compared to the control group from pretest to post-test phase. In the preparatory and throw phases (slow and fast throwing), higher activities of supraspinatus, lumbar erector spinae, upper trapezius, middle trapezius, latissimus dorsi, and pectoralis major were observed in the exercise group compared to the control group (P=0.05). Moreover, in the preparatory and throw phases, higher range of motion of shoulder flexion, forward flexion of shoulder, internal rotation of shoulder, external rotation of shoulder, and shoulder abduction were observed in the exercise group compared to the control group (P=0.05). Conclusion Corrective exercises can significantly alter shoulder kinematics and upper extremity muscle activity patterns in male handball players with UCS, which can be used in future studies to prevent UCS in handball players during throwing the ball.

Kinetics, Kinematics, and Muscle Activity Patterns During Back Squat With Different Contributions of Elastic Resistance.

Performing back squats with elastic bands has been widely used in resistance training. Although research demonstrated greater training effects obtained from adding elastic bands to the back squat, little is known regarding the optimal elastic resistance and how it affects neuromuscular performance. This study aimed to compare the force, velocity, power, and muscle activity during back squats with different contributions of elastic resistance. Thirteen basketball players performed 3 repetitions of the back squat at 85% of 1-repetition maximum across 4 conditions: (1)total load from free weightand (2)20%, (3)30%, and (4)40% of the total load from elastic band and the remaining load from free weight. The eccentric and concentric phases of the back squat were divided into upper, middle, and bottom phases. In the eccentric phase, mean velocity progressively increased with increasing elastic resistance, and muscle activity of the vastus medialis and rectus femoris significantly increased with the largest elastic resistance in the upper phase (P ≤ .036). In the concentric phase, mean power (P ≤ .021) and rate of force development (P ≤ .002) significantly increased with increasing elastic resistance. Furthermore, muscle activity of the vastus lateralis and vastus medialis significantly improved with the largest elastic resistance in the upper phases (P ≤ .021). Velocity, power, rate of force development, and selective muscle activity increased as the elastic resistance increased in different phases during the back-squat exercise.

Precise sensors in detecting stress in workers in the industry: A review

Stress in the work environment has an impact on worker welfare and industrial productivity. This paper reviews the use of precision sensors in detecting workers’ physiological responses to stress in industry. The focus is on sensors that measure heart rate, sweat rate, body temperature, muscle activity and sleep patterns. The wearable sensor is the main highlight. Despite implementation challenges, precision sensors offer the potential for real-time monitoring to create healthier and more productive work environments.

Electromyographic Insights and Simulations of Core Training in Compression Tights: Implications for Performance and Wearable Ergonomic

In exploring the performance-enhancing effects of compression sportswear, this study investigates its impact on trunk muscle activation during core stability training, with a particular focus on the biomechanical implications of this relationship. This research posits the existence of an Equilibrium Point of Motion (EPM) and employs surface Electromyography (EMG) to measure muscular responses in the Erector Spinae (ES), External Oblique (EO), and Rectus Abdominis (RA) during exercises performed with and without compression wear. Results revealed that compression garments significantly augment root mean square (RMS) values for ES and EO muscles, suggesting differential muscle activation patterns. Further, the application of OpenSim modeling of full-body musculoskeletal mechanics facilitated a novel analysis of muscle forces and activations, enhancing the understanding of sportswear functionality in an ergonomic context. This approach uncovered significant correlations between actual and simulated muscle activations, particularly for the ES and EO during a gluteal bridge exercise. These insights contribute to the development of ergonomically-engineered sportswear aimed at optimizing athletic performance and provide a valuable reference for future sportswear design and research.

Ab. No. 170 Impact of Dynamic Postural Exercises on Electromyographic Activity, Co-Contraction and Joint Position Sense in Upper Cross Syndrome: A Pilot Study

Introduction: A greater prevalence with no strong rehabilitation program for Upper Crossed Syndrome (UCS) accompanied the purpose to find out the efficacy of dynamic postural exercise developed on the basis of identification of muscle activation pattern in UCS.This will help in effective management of patients suffering from UCS. Methods: 14 subjects with diagnosed UCS were randomly allocated to experimental and control groups (N=14; n=7). Participants were asked to perform 4 exercises (YTWL) using elastic resistance band during which amplitude of muscle activation and cocontraction ratio with Surface electrodes using 4 channel electromyographic system were measured.12 muscles of both side (Upper, middle and lower trapezius, serratus anterior, pectoralis major, anterior scalene) were assessed. The intervention of experimental group consisted of seven exercises. Both groups were given hot pack, TENS and cervical AROM exercises. The intervention was prescribed for three days a week for 8 weeks. Cervical kinesthesia was measured using joint position sense error (JPSE) test. All the outcome variables were recorded at the baseline and after 8 weeks. Result: Statistically significant difference (p≤0.05) of mean amplitude in pre-post values of experimental group as well as between group were found. Between group analysis of UT:LT, SC:AS contraction ratio and joint position sense also found to be significant(p≤0.05). Conclusion: There was a significant improvement in mean amplitude and cocontraction of cervicothoracic muscles in Dynamic Postural Exercise group. Kinesthesia also improved in experimental group. Implications: A focused rehabilitation program for UCS will help in improving the quality of life and functional efficacy.

Embodied Harmony: Examining Yoga's Fundamental Links via Electromyographical Analysis of Pose and Trunk Muscle Activity

The present study, "Embodied Harmony: Investigating Core Connections in Yoga through Electromyographical Exploration of Postures and Trunk Muscle Activity," explores the complex interplay between trunk muscle activation patterns and yoga postures. The research examines how various yoga positions activate and alter core musculature using electromyography (EMG) as a tool. The results are intended to contribute to a better understanding of the physiological elements of yoga practice, shedding light on efficient training methods and possible therapeutic uses for those looking to strengthen and stabilize their core.

Exploring the Influence of Structured Familiarization to an Adjustable, Passive Load-Bearing Exoskeleton on Oxygen Consumption and Lower Limb Muscle Activation During Walking.

Walking patterns are modified during load carriage, resulting in an increased activation of lower limb muscles and energy expenditure. Negative effects of load carriage could be minimized by wearing an exoskeleton, but evidence on the effects are conflicting. The objectives of this study were to describe the influence of an adjustable, passive load-bearing exoskeleton on the metabolic cost of walking (MCW) and associated muscle activations, and to explore changes in MCW after a familiarization process. Thirteen participants walked on a treadmill with a 22.75 kg payload at six preselected speeds (from 0.67 to 1.56 m/s) under three walking conditions: 1) without exoskeleton (NoExo); 2) with exoskeleton before familiarization (ExoPre); and 3) with exoskeleton after familiarization (ExoPost). Metabolic data was normalized to walking speed to provide MCW. Multi-muscle surface electromyography (EMG) was time and amplitude normalized to the gait cycle to provide muscle activation patterns. The familiarization occurred over three weeks including exposure to the exoskeleton. Differences in MCW and muscle activations were compared using a nonparametric analysis of longitudinal data. There were statistically significant increases in MCW for all speeds in the ExoPre and ExoPost conditions compared the NoExo. The average muscle activation showed an increase during ExoPre and ExoPost for the three speeds evaluated. Post-hoc analysis showed no significant effect of the familiarization period on metabolic data. In conclusion, a first exposure to the adjustable exoskeleton increased MCW and muscle activations, but the familiarization process did not provide any benefits toward a reduction in MCW or reduction in muscle activations at all speeds evaluated.

Validation and Analysis of an Integrated Device for Recording Bite Force and Masseter Muscle Activity in Dentate Participants: An Observational Study

Introduction: The success of any prosthetic rehabilitation depends on acceptable occlusion and muscle coordination. Occlusal therapy should be an integral part of restorative and prosthetic treatment. A thorough diagnosis of bite force and muscle activity is required to ensure the patient’s masticatory function and comfort. The current system of digitisation lacks devices for the simultaneous evaluation of muscle activity and occlusal bite force, representing a significant limitation in understanding and managing restorative and rehabilitation therapy. Aim: To assess the efficacy of an ingeniously designed integrated device that records occlusal bite force and muscle activity. Materials and Methods: An observational study was conducted among 112 healthy volunteers in the Department of Prosthodontics at Sri Ramachandra Dental College and Hospital, Chennai, Tamil Nadu, India, for a period of one month and 45 days, from February 5, 2024 to March 20, 2024. The study aimed to validate the efficacy of a device designed to record bite force and muscle action potential simultaneously. The device consists of two key components: a square Forcesensitive Resistor (FSR) that records changes in resistance in response to applied force and a MyoWare 2.0 muscle sensor with Arduino (Advancer Technologies) for measuring the electrical activity of muscles. Study participants, aged between 21 and 35 years, were seated in an upright position. Muscle activity was recorded with surface electrodes placed on the masseter region, following Surface Electromyography for the Non Invasive Assessment of Muscles (SENIAM) guidelines, while a ground electrode was placed on the neck. Maximum Bite Force (MBF) was measured by placing intraoral pressure sensors, with recordings taken in maximum intercuspation three times, spaced one minute apart for each recording. Both muscle activity and bite force were recorded simultaneously. The Pearson’s correlation coefficient was used to evaluate the correlation between bite forces and muscle action potential with standard average values. Results: The results revealed a strong positive correlation between the masseter muscle activity action potential and the bite force values of the right molar (r=0.964, p&lt;0.001), left molar (r=0.980, p&lt;0.001) and incisor (r=0.550, p=0.002). Conclusion: The device synergistically records muscle activation patterns and bite force distribution, displaying the values in an integrated digital interface. The results of the study reveal that this device can serve as a diagnostic tool in prosthodontic treatment planning.

Ergonomic evaluation of upper extremities muscle activity pattern during 60-min smartphone texting.

Smartphone usage has increased rapidly in the last decade due to rapid technological advancements. This extensive usage of smartphones led to physiological problems and musculoskeletal disorders (MSD) due to inappropriate postures. Past studies have reported the effects/discomfort of smartphone usage for short periods, ranging from 3-20 min, which does not represent the current era of smartphone dependency (approximately 7-hr/day). This study was performed on fifty-four participants aged 20-28 with 1-hr smartphone texting in a sitting posture. Flexion angles, both sides (dominant and non-dominant) muscle activity (maximum voluntary contraction %) at sternocleidomastoid (SCM), upper-trapezius (TRP), extensor digitorum (EDM) and abductor pollicis brevis (APB) muscles, and subjective discomfort were analyzed. After 1-hr smartphone texting, the muscle activity at eight upper extremities: SCM (24.80%), TRP (29.45%), EDM (14.44%) and APB (19.87%) significantly (p < 0.001) increased by 1.5-1.9 times with 27.4±3.18° and 82.94±7.03° head and lower-arm flexion angles, respectively. The mechanical loads on the cervical spine increased by 4.6 times, and subjective discomfort by 3 times. Maintaining the same posture for a long duration causes postural stress, muscular imbalances, and discomfort, leading to MSD with increased cervical intervertebral disc pressure.

Neuromuscular basis of Drosophila larval rolling escape behavior.

When threatened by dangerous or harmful stimuli, animals engage in diverse forms of rapid escape behaviors. In Drosophila larvae, one type of escape response involves C-shaped bending and lateral rolling followed by rapid forward crawling. The sensory circuitry that promotes larval escape has been extensively characterized; however, the motor programs underlying rolling are unknown. Here, we characterize the neuromuscular basis of rolling escape behavior. We used high-speed, volumetric, Swept Confocally Aligned Planar Excitation (SCAPE) microscopy to image muscle activity during larval rolling. Unlike sequential peristaltic muscle contractions that progress from segment to segment during forward and backward crawling, muscle activity progresses circumferentially during bending and rolling escape behavior. We propose that progression of muscular contraction around the larva's circumference results in a transient misalignment between weight and the ground support forces, which generates a torque that induces stabilizing body rotation. Therefore, successive cycles of slight misalignment followed by reactive aligning rotation lead to continuous rolling motion. Supporting our biomechanical model, we found that disrupting the activity of muscle groups undergoing circumferential contraction progression leads to rolling defects. We use EM connectome data to identify premotor to motor connectivity patterns that could drive rolling behavior and perform neural silencing approaches to demonstrate the crucial role of a group of glutamatergic premotor neurons in rolling. Our data reveal body-wide muscle activity patterns and putative premotor circuit organization for execution of the rolling escape response.

Muscle activation and coordinated movements of infant rolling

Rolling is a critical step of infant development, encouraging muscle coordination and enabling independent exploration. Understanding muscle activity during infant rolling movements on a flat surface is necessary to more fully characterize how the rolling milestone is achieved. The purpose of this study was to determine infants’ muscle activation throughout roll initiation for six previously established coordinated movements. Thirty-eight healthy infants (age: 6.5 ± 0.7 months; 23M/15F) were enrolled in this IRB-approved in-vivo biomechanics study. Surface electromyography sensors recorded muscle utilization from the erector spinae, abdominal muscles, quadriceps, and hamstrings while infants rolled. Each rolling movement was categorized as one of six roll types, and the mean muscle activity was analyzed. All roll types required initial activation of all measured muscle groups. Movements featuring axial rotation of the torso relative to the pelvis required highly active erector spinae muscles. Movements featuring trunk and hip flexion required highly active abdominal muscles. Infants used distinct coordinated muscle activations to achieve the six different roll types on a flat surface. A foundational understanding of the different muscle activation patterns required during infant rolling will provide crucial insight into motor development. This study quantified muscle coordination required of infants to achieve rolling on a firm flat surface. Previous research indicates that the mechanical environment in which an infant is placed impacts muscle activity and body position during normal lying. Therefore, future work should explore if mechanical environments that differ from a flat and firm surface also influence these coordinated movements and muscle activations.