Timing Of Muscle Activity Research Articles

Increased hip adductor activation during sit-to-stand improves muscle activation timing and rising-up mechanics in individuals with hemiparesis

Long sit-to-stand (STS) time has been identified as a feature of impaired functional mobility. The changes in biomechanics of STS performance with simultaneous hip adductor contraction have not been studied, which may limit indications for use of hip adductor activation during STS training. Ten individuals with hemiplegia (mean age 61.8years, injury time 29.8±15.2months) performed the STS with and without squeezing a ball between two legs. The joint moments, ground reaction force (GRF), chair reaction force and movement durations and temporal index of electromyography were calculated from the control condition for comparison with those from the ball squeezing condition. Under the squeeze condition, reduced peak vertical GRF during the ascension phase with increased loading rate was observed in the nonparetic limb, and the peak knee extensor moment occurred earlier in the paretic. Earlier activation of tibialis anterior and gluteus maximus, and gluteus medius were found in squeeze STS. Squeezing a ball between limbs during STS increased the contraction timing of tibialis anterior, gluteus maximus, gluteus medius, and soleus as well as a more symmetric rising mechanics encourage the use of squeezing a ball between limbs during STS for individuals with hemiparesis.

Effect of muscle activation on dynamic responses of neck of pilot during emergency ejection: a finite element study.

To determine the effect of muscle activation on the dynamic responses of the neck of a pilot during simulated emergency ejections. A complete finite element model of the pilot's head and neck was developed and dynamically validated. Three muscle activation curves were designed to simulate different activation times and levels of muscles during pilot ejection: A is the unconscious activation curve of the neck muscles, B is the pre-activation curve, and C is the continuous activation curve. The acceleration-time curves obtained during ejection were applied to the model, and the influence of the muscles on the dynamic responses of the neck was investigated by analyzing both angles of rotation of the neck segments and disc stresses. Muscle pre-activation reduced fluctuations in the angle of rotation in each phase of the neck. Continuous muscle activation caused a 20% increase in the angle of rotation compared to pre-activation. Moreover, it resulted in a 35% increase in the load on the intervertebral disc. The maximum stress on the disc occurred in the C4-C5 phase. Continuous muscle activation increased both the axial load on the neck and the posterior extension angle of rotation of the neck. Muscle pre-activation during emergency ejection has a protective effect on the neck. However, continuous muscle activation increases the axial load and rotation angle of the neck. A complete finite element model of the pilot's head and neck was established and three neck muscle activation curves were designed to investigate the effects of muscle activation time and level on the dynamic response of the pilot's neck during ejection. This increased insights into the protection mechanism of neck muscles on the axial impact injury of the pilot's head and neck.

Mawangdui-Guidance Qigong Exercise for patients with chronic non-specific low back pain: Study protocol of a randomized controlled trial.

Worldwide, there is a high frequency of chronic non-specific low back pain (CNLBP), which is a significant public health concern. The etiology is complicated and diverse, and it includes a number of risk factors such as diminished stability and weak core muscles. Mawangdui-Guidance Qigong has been employed extensively to bolster the body in China for countless years. However, the effectiveness of treating CNLBP has not been assessed by a randomized controlled trial (RCT). In order to verify the results of the Mawangdui-Guidance Qigong Exercise and examine its biomechanical mechanism, we intend to perform a randomized controlled trial. Over the course of 4 weeks, 84 individuals with CNLBP will be randomly assigned to receive either Mawangdui-Guidance Qigong Exercise, motor control exercise, or medication (celecoxib). Electromyographic data, including muscle activation time, iEMGs, root mean square value (RMS) and median frequency (MF), will be the main outcomes. The Japanese Orthopedic Association (JOA) Score, the Mcgill Pain Questionnaire (MPQ), beta-endorphin, and substance P are examples of secondary outcomes. At the start of treatment and 4 weeks later, all outcomes will be evaluated. SPSS version 20.0 (SPSS Inc., Chicago, IL, USA) will be used for all of the analysis. The prospective findings are anticipated to offer an alternative treatment for CNLBP and provide a possible explanation of the mechanism of Mawangdui-Guidance Qigong Exercise on CNLBP. The Sichuan Regional Ethics Review Committee on Traditional Chinese Medicine has given the study approval (Approval No. 2020KL-067). It has also registered at the website of China Clinical Trial Center Registration. The application adheres to the Declaration of Helsinki's tenets (Version Edinburgh 2000). Peer-reviewed papers will be used to publicize the trial's findings. ClinicalTrials.gov, identifier ChiCTR2000041080.

Comparison of Functional Outcomes between Supervised Rehabilitation and Telerehabilitation in Female Patients with Patellofemoral Pain Syndrome during the COVID-19 Pandemic.

Patellofemoral pain syndrome (PFPS) is a common cause of anterior knee pain, and therapeutic exercises are recommended. During the COVID-19 pandemic, despite recommendations on the importance of telerehabilitation, insufficient studies have investigated functional outcomes between supervised rehabilitation and telerehabilitation in patients with PFPS. This study aimed to compare the muscle strength, muscle activation time, and patient-reported outcomes between supervised rehabilitation and telerehabilitation in female patients with PFPS. A total of 61 patients (supervised, n = 30; telerehabilitation, n = 31) participated. Muscle strength and activation time of the quadriceps and hamstrings were measured using an isokinetic device. Hip muscle strength was evaluated using a hand-held dynamometer. Patient-reported outcomes were measured using the visual analog scale (VAS) for pain, Kujala Anterior Knee Pain Scale (AKPS) for functional ability, and Tampa scale for kinesiophobia (TSK-11). No significant differences were found in muscle strength, muscle activation time, or patient-reported outcomes of the involved knees between the two groups (p > 0.05). In addition, the rate of change in all parameters did not significantly differ between the two groups (p > 0.05). Telerehabilitation, such as a home-exercise program supervised by physical therapists, may be as effective as supervised rehabilitation in improving functional outcomes in female patients with PFPS.

Comparing the Timing of Electromyographic Activity of Selected Lumbar-Pelvic Muscles During a Cross-cutting Maneuver in Football Players With Athletic Groin Pain and Healthy Peers

Background and Aims Athletic groin pain (AGP) is one of the most common injuries among athletes. It causes the use of compensatory mechanisms to adjust pain and affects lumbar-pelvic and hip movements, which leads to prolonging the pain healing process. This study aims to compare the timing of electromyographic activity in selected lumbar-pelvic muscles during a cross-cutting maneuver in football players with AGP and healthy peers. Methods In this quasi-experimental study, 28 football players in the second division league of Iran participated in two groups of control (n=14) and AGP (n=14). The timing of electromyography activity in the gluteus medius, adductor longus, rectus abdominis, multifidus, and transverse abdominis/internal oblique during a cross-cutting maneuver was recorded bilaterally with a one-minute interval since the time of foot-ground contact in two groups. Results The time for the onset of activity in the gluteus medius muscle in the dominant foot (P=0.033) and in the multifidus muscle in the opposite foot (P= 0.023) for the AGP group was significantly delayed in compared to the control group; however, the rectus abdominis muscle in the dominant foot was activated significantly earlier and before the heel contact with the ground (P=0.001). Conclusion It seems that AGP changes the timing of electromyographic muscle activity in football players. These changes and compensatory mechanisms may put the athletes at the potential risk of lower limb injuries. It is recommended to find solutions to reduce the effects of AGP and the resulting changes.

Hindlimb muscle spindles inform preparatory forelimb coordination prior to landing in toads.

Animals move across a wide range of surface conditions in real-world environments to acquire resources and avoid predation. To effectively navigate a variety of surfaces, animals rely on several mechanisms including intrinsic mechanical responses, spinal-level central pattern generators, and neural commands that require sensory feedback. Muscle spindle Ia afferents play a critical role in providing sensory feedback and informing motor control strategies across legged vertebrate locomotion, which is apparent in cases where this sensory input is compromised. Here, we tested the hypothesis that spindle Ia afferents from hindlimb muscles are important for coordinating forelimb landing behavior in the cane toad. We performed bilateral sciatic nerve reinnervations to ablate the stretch reflex from distal hindlimb muscles while allowing for motor neuron recovery. We found that toads significantly delayed the onset and reduced the activation duration of their elbow extensor muscle following spindle Ia afferent ablation in the hindlimbs. However, reinnervated toads achieved similar elbow extension at touchdown to that of their pre-surgery state. Our results suggest that while toads likely tuned the activation timing of forelimb muscles in response to losing Ia afferent sensation from the hindlimbs they were likely able to employ compensatory strategies that allowed them to continue landing effectively with reduced sensory information during take-off. These findings indicate muscle spindle Ia afferents may contribute to tuning complex movements involving multiple limbs.

IMPACTO DO FORTALECIMENTO DO CORE NA APTIDÃO FÍSICA EM JOVENS PRATICANTES DE JUDÔ

ABSTRACT Introduction To master judo skills, athletes must maintain maximum flexibility, agility, speed, and endurance. It is known that strength training can improve athletes’ competitive abilities and physical conditioning. Still, there is no consensus in the literature about the impacts of the CORE strengthening on the physical fitness of young judo practitioners. Objective Analyze the influence that CORE strengthens on the physical fitness of young judo practitioners. Methods 18 young athletes were randomly divided into a control training group, with routine activities, and an experimental training group, in which a protocol of core strengthening was also inserted. The article uses mathematical statistics to analyze the relationship between the physical conditioning of judo athletes and the structural characteristics of their technical training. Results No significant differences were identified between the two groups regarding muscle activation time or amplitude changes in the electrocardiogram (P>0.05). There was a significant difference in the results of the two groups in the static suspension test (P<0.05). The level of forearm endurance in the elite judokas group was higher than that in the common judo group(P<0.05). There is no apparent interaction between the forearm strength data (P>0.05). Conclusion It was found that strengthening the CORE can help improve the physical fitness of young judo athletes. More attention is recommended to young judo athletes by inserting CORE strengthening in their regular training. Evidence Level II; Therapeutic Studies - Investigating the result.

Coordination strategies of lower limb muscles during curve-turning tasks in preschool children

BackgroundPreschoolers are within their critical time in motion development; while muscles are the fundamental units in motion control and by monitoring activated intensity and duration of muscles, preschooler’s motor ability which would disclose their potential pathogenesis quality can be objectively and quantitatively assessed. Although a large number of studies were available on this issue, questions still being there: what are the patterns and characteristics of lower limb muscles when they are facing with the curve walking(CW) tasks; and then how individual muscle or muscle groups coordinated while turning curves. Our purpose of this study is first to portray the patterns and characteristics of lower limb muscles of healthy preschoolers while CW and then to insight their muscles’ coordination mechanism and "neuro-musculo-skeletal" feedback during motion. Method35 healthy preschoolers and 35 healthy adults’ lower limbs surface electromyography (sEMG) were collected while left and right CW and four muscle groups (Tibialis Anterior, Lateral Gastrocnemius, Rectus Femoris, and Biceps Femoris) were recorded. sEMG variables such as Muscle Activation Time, Total Duration of Activity Time, Average Muscle Activation Rate and Average Rate of Change were calculated. Paired sample t-test was used to explore the differences of sEMG variables between preschoolers and adults when turning curves. ResultsPreschoolers would adjust the gait by changing the activation time and activation rate to fulfill the curve turning tasks; but they also showed variations in coordination mechanism when contrasting with the adults group. Those findings in preschoolers would support to build muscles’ coordination mechanism and further insight to neuro-muscular skeletal feedback regulation. ConclusionAlthough preschoolers performed good enough to switching gait from normal walking to CW, but gaps in their abilities were still apparent when compared to adults. Hence, with the help of highly recognizable muscle coordination mechanism in CW, motor dysfunction in lower limbs of preschool children can be effectively identified.

Lower-limbs’ muscle coordination mechanism of healthy preschoolers while walking across obstacles

Research backgroundThe obstacle-crossing task is a complex gait task, it requires an advance predict of the obstacle for posture adjustment and accurate control of bilateral legs to ensure crossing the obstacles successfully. By monitoring the activated intensity and duration of muscles in this process, preschoolers' motor ability could be assessed objectively and quantitatively, as well as disclose their potential pathogenesis quality eventually. Scientific questionwhat are the patterns and characteristics of lower limb muscles when they are facing the obstacle-crossing walking (OW) tasks, and how they coordinate their individual muscle or muscle groups of lower-limbs muscles while walking across obstacles? Thereby, the purpose of this study was first to portray the patterns and characteristics of lower limb muscles of healthy preschoolers while OW motion and second to assess the muscles’ coordination mechanism. Method35 healthy preschoolers and 35 healthy adults’ lower limbs' surface electromyography (sEMG) were collected while left and right OW and four muscle groups (Tibialis Anterior, Lateral Gastrocnemius, Rectus Femoris, and Biceps Femoris) were recorded. sEMG variables such as Muscle Activation Time, Total Duration of Activity Time, Average Muscle Activation Rate, and Average Rate of Change were calculated. The paired sample-t-test was used to explore the differences of sEMG variables between preschoolers and adults when obstacle-crossing. ResultsPreschoolers would adjust the gait by changing the activation time and activation rate to fulfill the obstacle crossing tasks, but they also showed variations by contrasting to adults. Further, synergy between muscles in leg and thigh were also found. ConclusionAlthough preschoolers performed well enough to finish the OW tasks, ability gaps were still apparent when compared to adults. Hence, with the help of a deeply recognizable muscle coordination mechanism in OW, motor dysfunction in the lower limbs of preschool children can be effectively identified.

Muscle activation timing and knee biomechanics during single leg hop in subjects with and without anterior cruciate ligament reconstruction: a case study

The Single Leg Hop test (SLHT) is commonly performed to determine readiness to return to sport (RTS) after anterior cruciate ligament (ACL) injury and reconstruction [1]. Usually, the between-limb symmetry of hop distance is considered as a criterion to clear the athletes to RTS. However, athletes may pass this criterion despite ongoing biomechanical and neuromuscular deficits. Several works developed an instrumented approach of the SLHT to assess biomechanical parameters associated to ACL injury risk [1]. Although it is known that muscle pre-activation timing during landing can be altered in patients with ACL reconstruction (ACLR) [2], thus exposing them to a reinjury risk, very few studies have related biomechanical parameters with electromyographic (EMG) signals of the involved muscles. The aim of this preliminary study is to assess muscle pre-activation timing prior to SLHT landing in both ACLR and HC athletes and to associate this information with ACL injury-related kinematic and kinetic parameters. Two male soccer athletes (Tegner Activity Score ≥ 6) participated in the study, one healthy (HC) and one with ACLR (12 months before the test; injured limb: left). They performed three SLHT landing on a force plate (AMTI, USA, 1000 Hz) after standardized warm-up. The 3D trajectories of 52 markers were measured by an optoelectronic system (Vicon, 200 Hz) [3]. Eight wireless bipolar EMG electrodes (MiniWave, Cometa, Italy) were placed on Vastus Medialis (VM), Vastus Laterialis (VL), Semitendinous (ST) and Biceps femoris (BF) on both limbs according to the SENIAM guidelines [4]. All instruments were electronically synchronized. Foot-force plate contact was identified by setting a threshold of 20 N on the vertical GRF (vGRF) [5]. EMG onset prior to landing was identified according to [2]. A set of ACL injury risk-related parameters were then extracted: peak vGRF (vGRF peak ), peak knee flexion and abduction moment (KMflex peak KMabd peak ), and knee flexion at initial contact (KflexIC). Also, for each SLHT, the hop distance was assessed (SLH dist ). The Limb Symmetry Index (LSI) was then calculated for each parameter. For each athlete and each limb, the SLH with the greater hopping distance was considered for further data processing. Muscle pre-activation timing was shorter in ACLR subject than HC in all muscles (Table 1). ACLR subject also showed higher values in peak knee moments, especially in the injured limb, as well as greater asymmetry for most of the investigated parameters, especially knee angles and moments. In the ACLR subject, the lower muscle pre-activation timing prior to landing may lead to an uncoordinated movement and to a deficit in muscle force generation to stabilize the joint, thus increasing knee injury risk [2]. This timing was even shorter in the injured limb. From a biomechanical point of view, a greater asymmetry was found in the ACLR subject with respect to the HC in both kinematic and kinetic parameters. On the contrary, hop distance LSI did not show any clear difference between the two participants. These results corroborate the hypothesis that evaluating only hop distance is reductive.

Recruitment frequency of gastrocnemius lateralis in people with Parkinson’s disease during locomotion

Motor impairments are one of the most disabling symptoms related to Parkinson's disease (PD) and negatively affect quality of life [1]. Recently aberrant motor control in this population was investigated by means of surface electromyography (sEMG) in terms of timing of muscle activation [2]. Yet, insights on the recruitment frequency during gait are still lacking. Therefore, this study aims to characterize muscle recruitment frequency in PD with respect to healthy controls during walking. Twenty-five people with PD (age = 64 ± 10 years; BMI =26±3) and ten able bodied subjects (age = 62±6 years; BMI =28±3) were included and underwent sEMG while walking on a 8 m walkaway at BiomovLab (University of Padova, Italy). Three bilateral strides per subject were considered (105 strides in total). Electrical activity of gastrocnemius lateralis (GL) was recorded. To identify onset and offset of the muscle activation, the wavelet-based algorithm presented in [3] was adopted. Then, each signal was digitized in accordance with the detected activation timing (0 = no activation detected, 1 = activation detected) and used to provide activation maps [4] for both the assessed populations. The following Fig. 1 reports the activation map of GL activation for PD and control populations in function of the number of subjects of the specific population where muscular activity is observed. Horizontal bars are grey-level coded, according to the number of subjects of the population where a GL activity is detected; black = activity detected in all subjects, white = activity never detected. PD population presents a very frequent GL activity (close to 100%) between 35% and 55% of the gait cycle, as expected. A relatively poor activity is detected in the other gait cycle phases. Although GL in PD is more frequently recruited in the same gait cycle phase of controls (≈ 70%), healthy subjects displayed more homogeneous GL activity over the whole gait cycle. These outcomes seem to suggest that PD patients are characterized by a reduced ability to adapt to gait-related needs compared to age- matched control subjects.

Quantification of the Swallowing Mechanism Through Muscle Synergy Analysis.

Decreased swallowing function increases the risk of choking and aspiration pneumonia. Videofluoroscopy and computed tomography allow for detailed observation of the swallowing movements but have radiation risks. Therefore, we developed a method using surface electromyography (sEMG) to noninvasively assess swallowing function without radiation exposure. A 44-channel flexible sEMG sensor was used to measure the sEMG signals of the hyoid muscles during swallowing in 14 healthy young adult and 14 elderly subjects. Muscle synergy analysis was performed to extract the muscle synergies from the sEMG signals, and the three synergies were extracted from the hyoid muscle activities during the swallowing experiments. The experimental results showed that the three synergies represent the oral, early pharyngeal, and late pharyngeal swallowing phases and that swallowing strength is tuned by the strength of the muscle activities, whereas swallowing volume is controlled by adjusting muscle activation timing. In addition, the timing of the swallowing reflex is slower in elderly individuals. The results confirm that the proposed approach successfully quantifies swallowing function from sEMG signals, mapping the signals to the swallowing phases.

SEMG Analysis of Upper Limb Muscles during Backhand Smash Using Badminton Rackets of Different Stiffness

The analysis of racket stiffness effect on muscle activity during movement associated with badminton is essential for a better understanding of which badminton racket is better for the athletes to use. The present study aimed to evaluate the effect of racket stiffness on muscle activity and activation time of the upper limb muscles—biceps (Bicp), lateral head (TLat) and long head (TLong) of the triceps—when performing the backhand smash (BH) movement using two rackets with different levels of stiffness. A group of 6 volunteers, with an average age of 21.8 (±4.5) years, and an average badminton practice time of 10.7 (±5.3) years, performed 10 valid repetitions of the movement with each racket, and the muscle activity was collected using surface electromyography. Observing the results shows that the most excited muscle in the BH smash, in terms of (%MVC), is the TLat, regardless of the stiffness of the racket, which shows 56.9% for the Duora 33 and about 68.9% for the Duora 88, comparing with the Bicp and the TLong, respectively. Also, it was observed that the more rigid racket (Duora 88) showed a higher muscular activity for the Bicp and TLat muscles.

Surface Electromyographic Activity of the Rectus Abdominis and External Oblique during Isometric and Dynamic Exercises.

Exercises for the abdominal muscles are widely used in athletic activities for strength training and prevention of low back disorders. The timing and volume of muscle activation for various movements have not yet been clarified. The purpose of this research was to evaluate the surface electromyographic activity from the upper (RAU) and lower part (RAL) of the rectus abdominis and the external oblique (EO) muscles during eleven abdominal muscle strength training exercises. Thirty-five healthy male university students with a subspecialty in soccer participated in the study. They performed exercises involving isometric, concentric, and eccentric muscle contractions. The electromyographic recordings were amplified by a factor of 1000, rectified, and integrated. Mean integrated values were calculated by dividing the elapsed time for the five repetitions, to provide the mean integrated electromyographic values for each exercise. Leg movements from a long lying position showed higher activity of the rectus abdominis, compared to the EO (p < 0.001). The dynamic sit-ups showed an obvious dominant activity of the EO, compared to the rectus abdominis (p < 0.001). During eccentric exercise, higher activity was found in the RAU, compared to the RAL (p < 0.001). The results could serve as a basis for improving the design and specification of training exercises. Pre-exercises should be performed before testing abdominal muscle strength.

Do Compression Pants Influence Muscle Oscillation, Muscle Activation Time, And Oxygen Consumption During Running?

Do Compression Pants Influence Muscle Oscillation, Muscle Activation Time, And Oxygen Consumption During Running?

Feasibility of a Novel Video Game-Based Electromyography Biofeedback System in Patients With Knee Osteoarthritis.

A novel virtual game system Knee Biofeedback Rehabilitation Interface for game-based home therapy (KneeBright) was developed for strength training using integrated electromyography biofeedback of the quadriceps muscle to control the game. The study aimed to compare the KneeBright and electromyography biofeedback interface among patients with knee osteoarthritis. Controlled before and after design. Nineteen patients with knee osteoarthritis took part in this laboratory-based study. Exercise sessions took place on 2 separate days. During session 1, participants used a conventional electromyography biofeedback system while performing 3 sets of lower body exercises with emphasis on maximal muscle activation, endurance, and precision. During session 2, participants used the KneeBright game to match the exercise sets in the first session. For both sessions, knee extension torque during the isometric muscle activation exercises and time to voluntary additional exercise were recorded. Patient engagement was assessed using the technology acceptance model and System Usability Score questionnaires. The peak knee extension torque produced during the control exercise session and the KneeBright exercise session were positively correlated. Knee extension torque generated during KneeBright game exercise sessions was increased by an average of 25% compared to the control sessions (2.14 vs 1.77N·m/kg, P = .02). The mean technology acceptance model score for the KneeBright system was 3.4/5 and the mean System Usability Score was 79, both indicating positive patient engagement. Patients using the KneeBright game produced greater knee torque than patients using the conventional system, had positive levels of engagement, and exercised longer with the KneeBright game.

Tiempos de activación muscular frente a una desestabilización en pacientes con enfermedad de Parkinson en etapas iniciales

ObjectivesParkinson's disease (PD) generates a high incidence of falls, however, there is little evidence of instabilities in the initial stages. This investigation sought to compare the muscle activation times in patients with initial PD against a postural disturbance vs. a control group. Materials and methodsThe electromyographic activity (EMG) of 10 patients with PD in early stages (61.3 ±3.8 years) and a control group of 10 adults (62.2 ±3.0 year) was evaluated. The participants were subjected to a surface disturbance, which generated a stabilization response. The test was performed under 2conditions: eyes open (OA) v/s eyes closed (OC). Trunk (spinal erector) and lower extremity (soleus, tibialis anterior, femoral biceps, femoral rectus, adductor magnus, gluteus medius) muscle activation time was analyzed using surface EMG. ResultsThe PD group showed faster response times compared to the control group in the soleus muscle in OC (P=.04). This same muscle showed differences when comparing OA vs. OC only in the PD group (P=.04), showing a shorter response time in the OC condition. When comparing the spinal erector muscle, the PD group showed slower response times in the OA (P=.02) and OC (P=.04) conditions compared to the control group. ConclusionsMuscle activation times show that people with PD respond slower in the trunk muscles, while activation times decrease at the distal level. In the early stages, the slower responses at the trunk level could explain the onset of instability postural in these patients.

Males and females have different muscle activity patterns during gait after ACL injury and reconstruction

Kinematic and kinetic changes following anterior cruciate ligament (ACL) rupture and reconstruction (ACLR) have been fundamental to the understanding of mechanical disrupted load as it contributes to the development of posttraumatic osteoarthritis. These analyses overlook the potential contribution of muscle activity as it relates to the joint loading environment. Males and females classified as non-copers present with unique knee kinematics and kinetics after ACL injury. The purpose of this study was to perform sex-specific analyses in these individuals to explore muscle activity timing during gait after ACL rupture. Thirty-nine participants (12 females, 27 males) were enrolled. Muscle activity during gait was evaluated before and after pre-operative physical therapy, and six months after ACLR. Surface electromyography data were evaluated to determine timing (e.g., the time the muscle activity begins (‘On’) and ends (‘Off’)) for seven muscles: vastus lateralis and medialis (VL, VM), lateral and medial hamstrings (LH, MH), lateral and medial gastrocnemius (LG, MG), and soleus (SOL). General linear models with generalized estimating equations detected the effects of limb and time for muscle activity timing. Males presented with more limb asymmetries before and after pre-operative PT in the VL On (p < 0.001) and Off (p = 0.007), VM On and Off (p < 0.001), and MH off (p < 0.001), but all limb differences resolved by six months post ACLR. Changes in muscle activity in males were pervasive over time in both limbs. Females presented with no interlimb differences pre-operatively, and only involved limb VL off (p = 0.027) and VM off (p = 0.003) and the LH off in both limbs (p < 0.038) changed over time. Our data indicate that inter-limb differences in muscle activity across time points and changes in muscle activity timing over the course of physical therapy were sex specific. Males presented with more inter-limb differences in muscle activity across time points, and females presented with fewer asymmetries before and after pre-operative physical therapy. These data support that sex-specific adaptations should be taken into consideration when assessing biomechanical changes after ACLR.

The effect of vibration on kinematics and muscle activation during cycling

ABSTRACT Vibration has the potential to compromise performance in cycling. This study aimed to investigate the effects of vibration on full-body kinematics and muscle activation time series. Nineteen male amateur cyclists (mass 74.9 ± 5.9 kg, body height 1.82 ± 0.05 m, Vo2max 57 ± 9 ml/kg/min, age 27 ± 7 years) cycled (216 ± 16 W) with (Vib) and without (NoVib) vibration. Full-body kinematics and muscle activation time series were analysed. Vibration did not affect lower extremity joint kinematics significantly. The pelvic rotated with vibration towards the posterior direction (NoVib: 22.2 ± 4.8°, Vib: 23.1 ± 4.7°, p = 0.016, d = 0.20), upper body lean (NoVib: 157.8 ± 3.0°, Vib: 158.9 ± 3.4°, p = 0.001, d = 0.35) and elbow flexion (NoVib: 27.0 ± 8.2°, Vib: 29.4 ± 9.0°, p = 0.010, d = 0.28) increased significantly with vibration. The activation of lower extremity muscles (soleus, gastrocnemius lat., tibialis ant., vastus med., rectus fem., biceps fem.) increased significantly during varying phases of the crank cycle due to vibration. Vibration increased arm and shoulder muscle (triceps brachii, deltoideus pars scapularis) activation significantly over almost the entire crank cycle. The co-contraction of knee and ankle flexors and extensors (vastus med. – gastrocnemius lat., vastus med. – biceps fem., soleus – tibialis ant.) increased significantly with vibration. In conclusion vibrations influence main tasks such as propulsion and upper body stabilization on the bicycle to a different extent. The effect of vibration on the task of propulsion is limited due to unchanged lower body kinematics and only phase-specific increases of muscular activation during the crank cycle. Additional demands on upper body stabilization are indicated by adjusted upper body kinematics and increased muscle activation of the arm and shoulder muscles during major parts of the cranking cycle.

Investigation of variation factors in EMG measurement of swallowing: instruction can improve EMG reproducibility.

Variability in swallowing electromyography (EMG) has been reported to occur due to individual differences, even in studies with appropriate control of factors affecting EMG such as food type, properties, and posture. The increased variability broadens the confidence intervals of measures obtained from EMG, such as time and amplitude, and makes it difficult to detect differences in muscle activity. This makes it impossible to detect slight changes in swallowing function at an early stage, which is required for clinical examination. In this study, we focused on the tipper type and dipper type of oral swallows, which differ in the timing of muscle activity. The frequency of occurrence of both types varies between participants, and both types could occur in the same participant. In this study, we measured swallowing EMG wherein participants were instructed to swallow with a tipper and a dipper. The results showed that there was a significant difference in the between-participant duration between these two types of swallows. Within-participant variability was significantly lower in the tipper-dipper instruction condition compared to the baseline condition, which assumed a mixture of tipper-dipper swallowing. These results demonstrate that instructions on swallowing method are effective in improving the reproducibility of EMG.