Muscle Activation Characteristics Research Articles

Muscle Activity Characteristics of the Pronator Teres during Throwing in Baseball Pitchers: A Pilot Study.

The pronator teres muscle is a major dynamic stabilizer of elbow valgus stress during throwing. This study aims to investigate pronator teres muscle activation during breaking ball pitching in baseball pitchers. Twelve male college baseball players with more than eight years of baseball experience were included in this study. A wireless surface electromyography (EMG) system was used to measure the activation of the forearm muscles and record EMG data during fastball and curveball pitching. Peak pronator teres muscle activation during curveball pitching was greater than that during fastball pitching (p = 0.03). There was no difference in the muscle activation of the other forearm muscles (p > 0.05). These results indicate that increased muscle activity in the pronator teres may contribute to stiffness and induce pronator teres syndrome or medial elbow injuries related to the overuse of the pronator teres, especially during curveball pitching. Controlling curveball throws contributes to player coaching and conditioning for the prevention of elbow joint disorders and pronator teres syndrome.

Altering muscle activity in the lower extremities by bipedal landing with different drop tasks and shoes

BACKGROUND: The ability of the lower-extremity muscle activation directly affects the performance and in turn interacts with the loading conditions of the muscle itself. However, systematic information concerning the characteristics of lower-extremity muscle during landings is lacking. In particular, the landing height and shoes are also important factors based on the actual situation, which could further contribute to understanding the neuromuscular activity and how biochemical response of the body tissues to double-leg drop landings. OBJECTIVE: The study was to investigate the effects of landing tasks on the activation of lower-extremity muscles and explore the relationship among movement control, landing heights, shoe cushioning, and muscle activities. METHODS: Twelve male basketball players were recruited to perform drop jump (DJ) and passive landing (PL) from three heights (30, 45, and 60 cm) while wearing highly-cushioned basketball shoes (HC) and less-cushioned control shoes (LC). EMG electrodes were used to record the activities of the target muscles (rectus femoris, vastus lateralis, biceps femoris, tibialis anterior, and lateral gastrocnemius) during the landing tasks. RESULTS: Pre- and post-activation activity of the lower-extremity muscles significantly decreased during PL compared with those during DJ (p< 0.05). No significant shoe effects on the characteristics of muscle activation and coactivation during DJ movements were observed. However, the participants wearing LC showed significantly higher muscle post-activation (p< 0.05) at the three drop heights during PL compared with those wearing HC. Coactivation of the ankle muscles was higher in LC than in HC during 30-cm PL (p< 0.05). CONCLUSIONS: The activation patterns of lower-extremity muscles can be significantly influenced by landing types. Highly-cushioned basketball shoes would help reduce the risk of injuries by appropriately tuning the muscles during the PL.

Examination of hip function and muscle activity during clam exercise.

[Purpose] Clam exercise is commonly used to strengthen hip abductor muscles. This study aimed to classify the directions of greater trochanter movement during clam exercise and examine whether this classification reveals any differences in the characteristics of muscle activities. [Participants and Methods] Twenty healthy male participants were included and were divided into three groups according to the direction of greater trochanter movements during clam exercise: diagonally upward, backward, and upward. Muscle activity of the gluteus medius, gluteus maximus, tensor fascia lata, and external oblique was measured during clam exercise, along with the direction of greater trochanter movement and maximum muscle strength in the clam exercise limb position. [Results] In the diagonally upward group, the gluteus medius muscles showed higher activity than the other three muscles, and their activity was higher in the diagonally upward and backward groups than in the upward group. [Conclusion] The tension and action vector of the muscles changed due to differences in the direction of the greater trochanter movement caused by the movement pattern of each participant. The muscle activity around the hip joint changes with the direction of greater trochanter movement during clam exercise.

Relationship between muscle activity characteristics and physical therapy parameters during posterior gait assistance with knee-ankle-foot orthosis in severe acute stroke hemiplegic patients

Relationship between muscle activity characteristics and physical therapy parameters during posterior gait assistance with knee-ankle-foot orthosis in severe acute stroke hemiplegic patients

Influence of forward head posture on muscle activation pattern of the trapezius pars descendens muscle in young adults

Forward head posture (FHP) is a serious problem causing head and neck disability, but the characteristics of muscle activity during long-term postural maintenance are unclear. This study aimed to investigate a comparison of electromyography (EMG) activation properties and subjective fatigue between young adults with and without habitual FHP. In this study, we examined the changes in the spatial and temporal distribution patterns of muscle activity using high-density surface EMG (HD-SEMG) in addition to mean frequency, a conventional measure of muscle fatigue. Nineteen male participants were included in the study (FHP group (n = 9; age = 22.3 ± 1.5 years) and normal group (n = 10; age = 22.5 ± 1.4 years)). Participants held three head positions (e.g., forward, backward, and neutral positions) for a total of 30 min each, and the EMG activity of the trapezius pars descendens muscle during posture maintenance was measured by HD-SEMG. The root mean square (RMS), the modified entropy, and the correlation coefficient were calculated. Additionally, the visual analogue scale (VAS) was evaluated to assess subjective fatigue. The RMS, VAS, modified entropy, and correlation coefficients were significantly higher in the FHP group than in the normal group (p < 0.001). With increasing postural maintenance time, the modified entropy and correlation coefficient values significantly decreased, and the mean frequency and VAS values significantly increased (p < 0.001). Furthermore, the forward position had significantly higher RMS, correlation coefficient, modified entropy, and VAS values than in the neutral position (p < 0.001). The HD-SEMG potential distribution patterns in the FHP group showed less heterogeneity and greater muscle activity in the entire muscle and subjective fatigue than those in the normal group. Excess muscle activity even in the neutral/comfortable position in the FHP group could potentially be a mechanism of neuromuscular conditions in this population.

Muscle Activity During Scapular Muscle Exercises With Multijoint Compound Movement: Analysis Using Fine-Wire and Surface Electrodes.

Improvements in motor control of the scapular muscles are important for the prevention and rehabilitation of shoulder and elbow injuries in overhead athletes. To clarify scapular muscle activity during multijoint compound movement exercises using fine-wire and surface electrodes. Descriptive laboratory study. Sixteen healthy men performed 5 types of exercises (cat and dog, trunk rotation, A-exercise, T-exercise, and Y-exercise). Muscle activity was measured as percentage of maximum voluntary isometric contraction (%MVIC) by using fine-wire electrodes in the rhomboid major (Rhom) and using surface electrodes in the upper (UT), middle (MT), and lower (LT) trapezius and serratus anterior (SA) muscles. The Rhom/UT, MT/UT, LT/UT, and SA/UT muscle activity ratios were calculated. One-way analysis of variance was used to compare the %MVIC and muscle activity ratios between exercises. There was no significant difference in Rhom activity between the exercises (34.6-54.2%MVIC; P = .25). LT activity was significantly greater in the trunk rotation (58.0 ± 24.6%MVIC) and Y-exercise (63.2 ± 40.1%MVIC) than in the cat and dog scapular retraction (19.6 ± 9.3%MVIC) and A-exercise (28.2 ± 14.2%MVIC) (P < .05). SA activity was significantly greater in the cat and dog scapular protraction (26.7 ± 11.0%MVIC) and Y-exercise (25.6 ± 19.3%MVIC) than in the other exercises (P < .05). The SA/UT activity ratio in the cat and dog scapular protraction exercise (9.64 ± 8.48) was significantly higher than in the other exercises (P < .05). All the exercises were effective for activating the Rhom. The trunk rotation and Y-exercise were effective for activating the LT, and the cat and dog scapular protraction exercise was effective for activating the SA while suppressing the UT. These results enable exercise selection based on muscle activity characteristics (moderate [20%-50%MVIC] and high [>50%MVIC] levels contribute to muscle activation) to prevent and rehabilitate shoulder and elbow injuries.

Do individuals with knee osteoarthritis walk with distinct knee biomechanics and muscle activation characteristics? An investigation of knee osteoarthritis, hip osteoarthritis, and asymptomatic groups

BackgroundBiomechanical markers including reductions in sagittal plane kinematics and moments, increases in knee adduction moments (KAM), and altered muscle activations have been identified as hallmark indicators of knee osteoarthritis (OA). However, it remains unknown whether these features of knee OA gait are exclusive to the diseased joint. Research questionTo determine whether specific gait outcomes previously linked to symptomatic medial compartment knee OA are unique to knee OA by concurrently investigating a group of asymptomatic individuals and those with hip OA. Methods16 individuals with moderate medial compartment knee OA, 16 individuals with moderate hip OA, and 16 asymptomatic controls were recruited. Participants walked on a treadmill while segment kinematics and ground reaction forces were recorded. Sagittal plane kinematics and sagittal and frontal plane moments were calculated. Surface electromyograms were recorded from lateral and medial hamstrings and gastrocnemius and vastus lateralis and medialis. Discrete variable analysis was used to investigate knee joint mechanics and muscle activation ratios. Analysis of Variance models using Bonferroni corrections determined between group differences (α = 0.0167). ResultsSagittal plane knee kinematics and moments were statistically similar among all groups (p > 0.0167). No differences were found for peak KAM and impulse between knee OA and asymptomatic groups (p > 0.0167) but peak KAM (p = 0.006 and impulse (p = 0.001) were greater in the knee OA group compared to hip OA. The hip OA group had a lower KAM impulse (p < 0.0167) compared to the knee OA and asymptomatic groups. A greater LH:MH activation ratio (p < 0.0167) was found in the knee OA group compared to hip OA and asymptomatic groups. No other activation ratio differences were found (p > 0.0167). SignificanceMedial and lateral hamstring muscle activation levels may provide utility as a knee OA gait biomarker compared to biomechanical outcomes, quadriceps and gastrocnemius activation, when differentiating knee OA from asymptomatic and hip OA cohorts.

Abnormal synergies and associated reactions post-hemiparetic stroke reflect muscle activation patterns of brainstem motor pathways.

Individuals with moderate-to-severe post-stroke hemiparesis cannot control proximal and distal joints of the arm independently because they are constrained to stereotypical movement patterns called flexion and extension synergies. Accumulating evidence indicates that these synergies emerge because of upregulation of diffusely projecting brainstem motor pathways following stroke-induced damage to corticofugal pathways. During our recent work on differences in synergy expression among proximal and distal joints, we serendipitously observed some notable characteristics of synergy-driven muscle activation. It seemed that: paretic wrist/finger muscles were activated maximally during contractions of muscles at a different joint; differences in the magnitude of synergy expression occurred when elicited via contraction of proximal vs. distal muscles; and associated reactions in the paretic limb occurred during maximal efforts with the non-paretic limb, the strength of which seemed to vary depending on which muscles in the non-paretic limb were contracting. Here we formally investigated these observations and interpreted them within the context of the neural mechanisms thought to underlie stereotypical movement patterns. If upregulation of brainstem motor pathways occurs following stroke-induced corticofugal tract damage, then we would expect a pattern of muscle dependency in the observed behaviors consistent with such neural reorganization. Twelve participants with moderate-to-severe hemiparetic stroke and six without stroke performed maximal isometric torque generation in eight directions: shoulder abduction/adduction and elbow, wrist, and finger flexion/extension. Isometric joint torques and surface EMG were recorded from shoulder, elbow, wrist, and finger joints and muscles. For some participants, joint torque and muscle activation generated during maximal voluntary contractions were lower than during maximal synergy-induced contractions (i.e., contractions about a different joint), particularly for wrist and fingers. Synergy-driven contractions were strongest when elicited via proximal joints and weakest when elicited via distal joints. Associated reactions in the wrist/finger flexors were stronger than those of other paretic muscles and were the only ones whose response depended on whether the non-paretic contraction was at a proximal or distal joint. Results provide indirect evidence linking the influence of brainstem motor pathways to abnormal motor behaviors post-stroke, and they demonstrate the need to examine whole-limb behavior when studying or seeking to rehabilitate the paretic upper limb.

Finite element human body models with active reflexive muscles suitable for sex based whiplash injury prediction.

Previous research has not produced a satisfactory resource to study reflexive muscle activity for investigating potentially injurious whiplash motions. Various experimental and computational studies are available, but none provided a comprehensive biomechanical representation of human response during rear impacts. Three objectives were addressed in the current study to develop female and male finite element human body models with active reflexive neck muscles: 1) eliminate the buckling in the lower cervical spine of the model observed in earlier active muscle controller implementations, 2) evaluate and quantify the influence of the individual features of muscle activity, and 3) evaluate and select the best model configuration that can be used for whiplash injury predictions. The current study used an open-source finite element model of the human body for injury assessment representing an average 50th percentile female anthropometry, together with the derivative 50th percentile male morphed model. Based on the head-neck kinematics and CORelation and Analyis (CORA) tool for evaluation, models with active muscle controller and parallel damping elements showed improved head-neck kinematics agreement with the volunteers over the passive models. It was concluded that this model configuration would be the most suitable for gender-based whiplash injury prediction when different impact severities are to be studied.

Characteristics of Lower Extremity Muscle Activation in Response to Change in Inclination while Walking on a Treadmill

Treadmill walking is a popular form of exercise that offers many benefits to its users, such as improvements in cardiovascular health and gait patterns. Few research studies have explored muscle activation of various lower extremity joints at different levels of inclination on a treadmill. Therefore, this study aims to further characterize muscle activation during gait in healthy individuals in response to changes in treadmill inclination at a constant speed. Twenty healthy participants (24.5 ± 4.3 years of age) were recruited for this study. Participants were instructed to walk on a treadmill at six different inclines (0%, 3%, 6%, 9%, 12%, and 15%) while maintaining a constant speed of 3.4 mph. Muscle activation of the tibialis anterior (TA), gastrocnemius (GA), gluteus maximus (GMAX), gluteus medius (GMED), vastus medialis (QUADS), and biceps femoris (HS) were collected using surface EMG. There were slight differences in muscle activation between the muscle groups during the various intervals. However, there were no significant differences between muscle groups. The results revealed that the extensor muscles (GA, HS, and GMAX) of the lower extremity showed trends of longer activation periods with an increase in inclination. This study found that as inclination increases, activation of the extensor muscles of the lower extremity also increases while walking on a treadmill. The findings of this study will serve as a baseline for research to compare populations with known gait impairments, such as individuals with HIV, post-stroke, or the elderly, to better understand EMG analysis leading to gait deviations or abnormalities with neuromuscular activation.

Towards Evaluating Pitch-Related Phonation Function in Speech Communication Using High-Density Surface Electromyography

Pitch, as a sensation of the sound frequency, is a crucial attribute toward constructing a natural voice for communication. Producing intelligible sounds with normal pitches depend on substantive interdependencies among facial and neck muscles. Clarifying the interrelations between the pitches and the corresponding muscular activities would be helpful for evaluating the pitch-related phonating functions, which would play a significant role both in training pronunciation and in assessing dysphonia. In this study, the speech signals and the high-density surface electromyography (HD sEMG) signals were synchronously acquired when phonating [a:], [i:], and [ә:] vowels with increasing pitches, respectively. The HD sEMG energy maps were constructed based on the root mean square values to visualize spatiotemporal characteristics of facial and neck muscle activities. Normalized median frequency (nMF) and root-mean square (nRMS) were correspondingly extracted from the speech and sEMG recordings to quantitatively investigate the correlations between sound frequencies and myoelectric characteristics. The results showed that the frame-wise energy maps built from sEMG recordings presented that the muscle contraction strength increased monotonously across pitch-rising, with left-right symmetrical distribution for the face/neck. Furthermore, the nRMS increased at a similar rate to the nMF when there were rising pitches, and the two parameters had a significant correlation across different vowel tasks [(a:) (0.88 ± 0.04), (i:) (0.89 ± 0.04), and (ә:) (0.87 ± 0.05)]. These findings suggested the possibility of utilizing muscle contraction patterns as a reference for evaluating pitch-related phonation functions. The proposed method could open a new window for developing a clinical approach for assessing the muscular functions of dysphonia.

Gluteus Maximus Muscle Activation Characteristics During a Chair-Rise in Adults With Chronic Stroke.

A successful chair-rise is an important indicator of functional independence post-stroke. Lower extremity electromyographic analyses provide a basis for muscle activation from which clinical intervention protocols may be derived. Gluteus maximus activation during the chair-rise has not been thoroughly researched in the chronic stroke population. This study investigated the magnitude and onset of gluteus maximus activation during the chair-rise comparing adults post-stroke with healthy controls. In this cross-sectional study, adults with chronic stroke (n = 12) and healthy controls (n = 12) completed 4 natural-speed chair-rise trials. Magnitude and onset of bilateral gluteus maximus activation were measured during the movement with secondary comparative data from biceps femoris and vastus lateralis muscles. Kinetic and kinematic measurements were used to quantify chair-rise phases and movement cycle duration. Significant decreases in paretic ( P = 0.002), and nonparetic ( P = 0.001) gluteus maximus magnitudes were noted post-stroke compared with ipsilateral extremities of healthy adults. Significant gluteus maximus onset delays were noted in paretic extremities compared with nonparetic extremities post-stroke ( P = 0.009) that were not apparent in comparative muscles. Similar onset times were noted when comparing the paretic extremity post-stroke to the ipsilateral extremity of healthy controls ( P = 0.714) despite prolonged movement cycle durations in those with chronic stroke ( P = 0.001). No onset delays were evident in the biceps femoris ( P = 0.72) or vastus lateralis ( P = 0.338) muscles. Despite apparent unilateral muscle weakness post-stroke, bilateral decreases in gluteus maximus activation magnitudes and compounding onset deficits of the paretic extremity were observed during chair-rising. Further research is needed to determine whether interventions maximizing bilateral activation magnitudes and improving temporal activation congruency during chair-rising will carry over to functional gainsVideo Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A387 ).

Evaluating Electromyography and Sonomyography Sensor Fusion to Estimate Lower-Limb Kinematics Using Gaussian Process Regression

Research on robotic lower-limb assistive devices over the past decade has generated autonomous, multiple degree-of-freedom devices to augment human performance during a variety of scenarios. However, the increase in capabilities of these devices is met with an increase in the complexity of the overall control problem and requirement for an accurate and robust sensing modality for intent recognition. Due to its ability to precede changes in motion, surface electromyography (EMG) is widely studied as a peripheral sensing modality for capturing features of muscle activity as an input for control of powered assistive devices. In order to capture features that contribute to muscle contraction and joint motion beyond muscle activity of superficial muscles, researchers have introduced sonomyography, or real-time dynamic ultrasound imaging of skeletal muscle. However, the ability of these sonomyography features to continuously predict multiple lower-limb joint kinematics during widely varying ambulation tasks, and their potential as an input for powered multiple degree-of-freedom lower-limb assistive devices is unknown. The objective of this research is to evaluate surface EMG and sonomyography, as well as the fusion of features from both sensing modalities, as inputs to Gaussian process regression models for the continuous estimation of hip, knee and ankle angle and velocity during level walking, stair ascent/descent and ramp ascent/descent ambulation. Gaussian process regression is a Bayesian nonlinear regression model that has been introduced as an alternative to musculoskeletal model-based techniques. In this study, time-intensity features of sonomyography on both the anterior and posterior thigh along with time-domain features of surface EMG from eight muscles on the lower-limb were used to train and test subject-dependent and task-invariant Gaussian process regression models for the continuous estimation of hip, knee and ankle motion. Overall, anterior sonomyography sensor fusion with surface EMG significantly improved estimation of hip, knee and ankle motion for all ambulation tasks (level ground, stair and ramp ambulation) in comparison to surface EMG alone. Additionally, anterior sonomyography alone significantly improved errors at the hip and knee for most tasks compared to surface EMG. These findings help inform the implementation and integration of volitional control strategies for robotic assistive technologies.

A Comparison of the Muscle Activation, Proprioception and Anthropometric Characteristics of the Dominant and Non-dominant Wrists

Purpose: Manual asymmetry refers to tendency that is in favor of hand to perform manual tasks requiring skills, it is important in every sensory and motor function. This study aimed to compare the muscle activation, proprioception, and anthropometric characteristics of the dominant and non-dominant wrists. &#x0D; Methods: In the study, forty young individuals aged between 18-25 years, who volunteered to participate, were included. As anthropometric measurements, the upper extremity length measurement forearm length measurement, hand length measurement wrist diameter measurement, hand width, shape and digit index measurements were performed, respectively. The muscle strength of wrist flexor and extensor muscles was measured by a hand dynamometer, while their muscle activations were measured by electromyography. The arm carrying angle was evaluated by a universal goniometer. &#x0D; Results: The mean age of the individuals included in the study was 22.51 ± 0.35 years. In the right dominant individuals, when the dominant and non-dominant sides were compared, a statistically significant difference was found between flexor muscle activations, muscle strength, and hand width (p0.05). &#x0D; Conclusion: Finding the dominant side's wrist flexor muscle activations, extensor muscle strength, and hand widths better in young individuals showed that the dominant side was frequently used in daily living activities. The difference was seen that the non-dominant side would be weaker and at higher risk of deformity with increasing age and in the presence of any rheumatic, orthopedic, and neurologic diseases.

Association between masticatory muscle activity and oral conditions in young female college students.

The purpose of this study was to determine the characteristics of masticatory muscle activity and various oral condition factors, and to analyze their associations in order to improve the prevention and diagnosis of masticatory muscle-related diseases. This study included 30 Korean females (mean age of 20 years, age range of 19–21 years). Participants were instructed to complete a self-written questionnaire on factors that may affect their muscle activity. Surface electromyography was used to measure the activity of the masseter and temporalis muscles. We also observed the buccal mucosa ridge, tongue indentation, tooth cracks and fractures, and mandibular tori in the oral cavity. Spearman correlation analysis and the nonparametric Mann–Whitney U test were applied to the data. When subjects had temporomandibular disorder, the right temporalis muscle exhibited significantly lower activity (P<0.05). Those who had received orthodontic treatment within the previous 2 years showed significantly lower activity of the left masseter muscle (P<0.05). Those who had a left buccal mucosa ridge exhibited lower activity of the left masseter muscle and higher activity of the right temporalis muscle compared with those without such a ridge (P<0.05). Participants with no tongue indentation showed significantly higher activity in the left masseter muscle (P<0.05). These results indicate that there are relationships between masticatory muscle activity and various factors related to the oral condition.

Cervical Muscle Activation Characteristics and Head Kinematics in Males and Females Following Acoustic Warnings and Impulsive Head Forces.

Sex, head and neck posture, and cervical muscle preparation are contributing factors in the severity of head and neck injuries. However, it is unknown how these factors modulate the head kinematics. In this study, twenty-four (16 male and 8 female) participants experienced 50 impulsive forces to their heads with and without an acoustic warning. Female participants demonstrated a 71 ms faster (p = 0.002) muscle activation onset compared to males after warning. The magnitude of muscle activation was not significant between sexes. Females exhibited 21% (p < 0.008) greater peak angular velocity in all force directions and 18% (p < 0.04) greater peak angular acceleration in sagittal plane compared to males. Females exhibited 15% (p = 0.03) greater peak linear acceleration compared to males only in sagittal flexion. Preparation attenuated head kinematics significantly (p < 0.03) in 11 out of 18 investigated head kinematics for both sexes. A warning eliciting a startle response 420 ms prior to the impact resulted in significant attenuation of all measured head kinematics in sagittal extension (p < 0.037). In conclusion, both sex and warning type were significant factors in head kinematics. These data provide insight into the complex relationship of muscle activation and sex, and may help identify innovative strategies to reduce head and neck injury risk in sports.

Postural Balance in Individuals With Knee Osteoarthritis During Stand-to-Sit Task.

Objective: Stand-to-sit task is an important daily function, but there is a lack of research evidence on whether knee osteoarthritis (knee OA) affects the postural balance during the task. This study aimed to compare individuals with knee OA and asymptomatic controls in postural balance and identify kinematic and lower extremity muscle activity characteristics in individuals with knee OA during the stand-to-sit task.Methods: In total, 30 individuals with knee OA and 30 age-matched asymptomatic controls performed the 30-s Chair Stand Test (30sCST) at self-selected speeds. Motion analysis data and surface electromyography (sEMG) were collected while participants performed the 30sCST. To quantify postural balance, the displacement of the center of mass (CoM) and the peak instantaneous velocity of the CoM were calculated. The kinematic data included forward lean angles of the trunk and pelvic, range of motion (RoM) of the hip, knee, and ankle joints in the sagittal plane. The averaged activation levels of gluteus maximus, vastus lateralis, vastus medialis, rectus femoris, biceps femoris (BF), tibialis anterior (TA), and medial head of gastrocnemius muscles were indicated by the normalized root mean square amplitudes.Results: Compared with the asymptomatic control group, the knee OA group prolonged the duration of the stand-to-sit task, demonstrated significantly larger CoM displacement and peak instantaneous CoM velocity in the anterior-posterior direction, reduced ankle dorsiflexion RoM, greater anterior pelvic tilt RoM, and lower quadriceps femoris and muscles activation level coupled with higher BF muscle activation level during the stand-to-sit task.Conclusion: This study indicates that individuals with knee OA adopt greater pelvic forward lean RoM and higher BF muscle activation level during the stand-to-sit task. However, these individuals exist greater CoM excursion in the anterior-posterior direction and take more time to complete the task. This daily functional activity should be added to the rehabilitation goals for individuals with knee OA. The knee OA group performs reduced ankle dorsiflexion RoM, quadriceps femoris, and TA activation deficit. In the future, the rehabilitation programs targeting these impairments could be beneficial for restoring the functional transfer in individuals with knee OA.

Preliminary Assessment of Muscle Activity and Muscle Characteristics during Training with Powered Robotic Exoskeleton: A Repeated-Measures Study.

A variety of robotic exoskeletons have been developed for patients with spinal cord injuries. However, the optimal training method and period for using a robotic exoskeleton have been uncertain until now. The purpose of this study is to determine the minimum training period for using a robotic exoskeleton with minimal muscle activity by investigating the changes in muscle activity and muscle characteristics of healthy adults during robotic exoskeleton training. A total of 16 people participated in the study. The robotic exoskeleton locomotion training consisted of three 50-min sessions a week for 7 weeks. The assessment consisted of sitting, standing, wide standing, sit-to-stand, and stand-to-sit where muscle activity and muscle characteristics were measured during each motion. All measurements were performed in the first session and every five sessions. Participants showed decreased muscle activity up to 10 sessions of training in the standing position, and 15 sessions in sit-to-stand and stand-to-sit motions. Upper extremity muscles showed decreased muscle activity, tone, stiffness, and logarithmic decrement up to the 15th session. The study results show that at least 15 training sessions are required to use the robotic exoskeleton with minimal load on the musculoskeletal system, and longer training is required for patients with spinal cord injury.

Cross-sectional Study of EMG and EMG Rise During Fast and Slow Hamstring Exercises.

BackgroundHamstring injuries remain a major burden in football while the effective prevention exercise the Nordic Hamstring is poorly adopted, despite the added positive effects on performance. Better understanding of hamstring function during Nordic Hamstring compared to other exercises may provide better insight to the physiological adaptations of different types of hamstring curls.PurposeThis cross-sectional study therefore aimed to compare the Nordic Hamstring curl with a conventional prone Leg Curl at different loads, and novel high velocity Hamstring Catches; in terms of peak normalized electromyographical activity (nEMG) and rate of electromyographic rise (RER) of Biceps Femoris long head, and angular velocity of the knee.Study designCross-sectional study.MethodsOut of 28 participants enrolled, the final sample included 23 recreationally active male participants who attended a session for determining RM (repetition maximum) to establish loading (8 and 16RM for Hamstring Catches, and 8, 16 and 24RM for Leg Curl) and to familiarize themselves with the three different exercises (Nordic Hamstring, Leg Curl and Hamstring Catch), and a testing session >4 days after during which EMG data were collected during 3 repetitions of each exercise performed in a random order.ResultsThe Nordic Hamstring evoked higher RER (1091.8 nEMG/s) than Hamstring Catches (mean difference: 421 nEMG/s, p<0.0001) and Leg Curl (mean difference: 705 nEMG/s, p<0.001), and at the earliest numerical timepoint from onset of muscle contraction (the Nordic Hamstring: 6 ms; Hamstring Catches: 36-41 ms; Leg Curl: 12-14 ms). Hamstring Catches displayed high peak angular velocity (mean: 471°/s). There was no difference in peak nEMG, irrespective of load for Leg Curl (8, 16 or 24RM) or Hamstring Catches (8- or 16RM).ConclusionThe Nordic Hamstring displayed the highest level muscle activity and most explosive recruitment characteristics with early and high rate of electromyographic rise, compared to even high velocity exercises, thus providing a possible mechanism by which it may increase performance and reduce injuries.Levels of evidence3What is known about the subjectEarly phase force and muscle recruitment have been linked to both performance and hamstring-related inhibition and fatiguability. However, the potential for different hamstring exercises to elicit explosive recruitment is unknown.What this study adds to existing knowledgeEarly phase recruitment was higher and faster during the Nordic Hamstring exercise compared with conventional hamstring Leg Curl exercises with different loads and a high-velocity hamstring exercise.Clinical RelevanceThe surprisingly fast and explosive recruitment characteristics during the Nordic Hamstring exercise suggests the possibility that this exercise have the potential to improve the rate of force development and perhaps counter the effects of hamstring-related inhibition and fatigue.

Gait risk factors for disease progression differ between non-traumatic and post-traumatic knee osteoarthritis

To examine if relationships between knee osteoarthritis (OA) progression with knee moments and muscle activation during gait vary between patients with non-traumatic and post-traumatic knee OA. This longitudinal study included participants with non-traumatic (n=17) and post-traumatic (n=18) knee OA; the latter group had a previous anterior cruciate ligament rupture. Motion capture cameras, force plates, and surface electromyography measured knee moments and lower extremity muscle activation during gait. Cartilage volume change were determined over 2 years using magnetic resonance imaging in four regions: medial and lateral plateau and condyle. Linear regression analysis examined relationships between cartilage change with gait metrics (moments, muscle activation), group, and their interaction. Measures from knee adduction and rotation moments were related to lateral condyle cartilage loss in both groups, and knee adduction moment to lateral plateau cartilage loss in the non-traumatic group only [β=-1.336, 95% confidence intervals (CI)=-2.653 to-0.019]. Generally, lower levels of stance phase muscle activation were related to greater cartilage loss. The relationship between cartilage loss in some regions with muscle activation characteristics varied between non-traumatic and post-traumatic groups including for: lateral hamstring (lateral condyle β=0.128, 95%CI=0.003 to 0.253; medial plateau β=0.199, 95%CI=0.059 to 0.339), rectus femoris (medial condyle β=-0.267, 95%CI=-0.460 to-0.073), and medial hamstrings (medial plateau; β=-0.146, 95%CI=-0.244 to-0.048). Findings indicate that gait risk factors for OA progression may vary between patients with non-traumatic and post-traumatic knee OA. These OA subtypes should be considered in studies that investigate gait metrics as risk factors for OA progression.