Peak Muscle Activity Research Articles

Comparison of muscle activation during quadrupedal movement training and traditional bodyweight exercises

Quadrupedal movement training (QMT) is a unique form of bodyweight training shown to improve flexibility, FMS scores, and proprioception, however, little is known about its muscle activation characteristics. Therefore, the purpose of this study was to compare surface EMG (sEMG) activity of muscles of the trunk, upper, and lower extremity during QMT movements and common traditional bodyweight exercises (TRA). Twenty (males n = 9) participants (age: 27.5 ± 10.8 yrs, height: 169.0 ± 7.0 cm, mass: 66.6 ± 10.9 kg) were prepped and fitted with sEMG electrodes on their right-side bicep brachii, medial deltoid, triceps brachii, pectoralis major, latissimus dorsi, rectus abdominus, rectus femoris and bicep femoris. Following completion of maximal voluntary isometric contraction (MVIC) tests for normalization, participants performed 4 repetitions of 8 QMT exercises (from the Animal Flow™ system) and 3 TRA exercises (pushup, squat and forearm plank) in random order. The pooled peak muscle activations of all QMT exercises resulted in moderate (21–40% MVIC) to very high (>60% MVIC) peak muscle activation levels for each muscle group with significantly higher (p > 0.05) muscle activation for the biceps (47.72 ± 21.41%), deltoid (66.58 ± 11.39%), and latissimus dorsi (62.81 ± 18.14%) than the pushup (23.31 ± 16.95, 45.63 ± 18.59, 29.17 ± 20.58% respectively) and significantly higher activation of the bicep femoris (41.89 ± 13.83%) than the squat (17.79 ± 11.12%). TRA (pushup) showed significantly higher activation of the triceps and pectoralis. There were no differences in rectus femoris or rectus abdominus. Muscle activation levels during QMT are comparable to or higher than common traditional bodyweight exercises and therefore may be an appealing strategy for training multiple muscle groups simultaneously.

Muscle recruitment during gait in individuals with unilateral transfemoral amputation due to trauma compared to able-bodied controls.

Individuals with transfemoral lower limb amputations walk with adapted gait. These kinetic and kinematic compensatory strategies will manifest as differences in muscle recruitment patterns. It is important to characterize these differences to understand the reduced endurance, reduced functionality, and progression of co-morbidities in this population. This study aims to characterize muscle recruitment during gait of highly functional individuals with traumatic transfemoral amputations donning state-of-the-art prosthetics compared to able-bodied controls. Inverse dynamic and static optimisation methods of musculoskeletal modelling were used to quantify muscle forces of the residual and intact limb over a gait cycle for 11 individuals with traumatic transfemoral amputation and for 11 able-bodied controls. Estimates of peak muscle activation and impulse were calculated to assess contraction intensity and energy expenditure. The generalized estimation equation method was used to compare the maximum values of force, peak activation, and impulse of the major muscles. The force exhibited by the residual limb's iliacus, psoas major, adductor longus, tensor fasciae latae and pectineus is significantly higher than the forces in these muscles of the intact contralateral limb group and the able-bodied control group (p < 0.001). These muscles appear to be recruited for their flexor moment arm, indicative of the increased demand due to the loss of the plantar flexors. The major hip extensors are recruited to a lesser degree in the residual limb group compared to the intact limb group (p < 0.001). The plantar flexors of the intact limb appear to compensate for the amputated limb with significantly higher forces compared to the able-bodied controls (p = 0.01). Significant differences found in impulse and peak activation consisted of higher values for the limbs (residual and/or intact) of individuals with transfemoral lower limb amputations compared to the able-bodied controls, demonstrating an elevated cost of gait. This study highlights asymmetry in hip muscle recruitment between the residual and the intact limb of individuals with transfemoral lower limb amputations. Overall elevated impulse and peak activation in the limbs of individuals with transfemoral amputation, compared to able-bodied controls, may manifest in the reduced walking endurance of this population. This demand should be minimised in rehabilitation protocols.

Neuromuscular adaptations to perturbation-based balance training using treadmill belt accelerations do not transfer to an obstacle trip in older people: A cross-over randomised controlled trial

BackgroundThis study examined (i) adaptations in muscle activity following perturbation-based balance training (PBT) using treadmill belt-accelerations or PBT using walkway trips and (ii) whether adaptations during treadmill PBT transfer to a walkway trip. MethodsThirty-eight older people (65+ years) undertook two PBT sessions, including 11 treadmill belt-accelerations and 11 walkway trips. Surface electromyography (EMG) was measured bilaterally on the rectus femoris (RF), tibialis anterior (TA), semitendinosus (ST) and gastrocnemius medial head (GM) during the first (T1) and eleventh (T11) perturbations. Adaptations (within-subjects - 1st vs 11th perturbations for treadmill and walkway PBT) and their transfer (between-subjects – 1st walkway trip after treadmill PBT vs 1st walkway trip with no prior training) effects were examined for the EMG parameters. ResultsTreadmill PBT reduced post-perturbation peak muscle activation magnitude (left RF, TA, ST, right RF, ST, GM), onset latency (right TA), time to peak (right RF) and co-contraction index (knee muscles) (P < 0.05). Walkway PBT reduced post-trip onset latencies (right TA, ST), peak magnitude (left ST, right GM), time to peak (right RF, ST) and pre-perturbation muscle activity (right TA) (P < 0.05). Those who undertook treadmill PBT were not different to those without prior training during the first walkway trip (P > 0.05). ConclusionsBoth treadmill and walkway PBT induced earlier initiation and peak activation of right limb muscles responsible for the first recovery step. Treadmill PBT also reduced co-contraction of the knee muscles. Adaptations in muscle activity following treadmill PBT did not transfer to a walkway trip.

Changing the Mandibular Position in Rowing: A Brief Report of a World-Class Rower.

We investigated the acute biophysical responses of changing the mandibular position during a rowing incremental protocol. A World-class 37-year-old male rower performed two 7 × 3 min ergometer rowing trials, once with no intraoral splint (control) and the other with a mandibular forward repositioning splint (splint condition). Ventilatory, kinematics and body electromyography were evaluated and compared between trials (paired samples t-test, p ≤ 0.05). Under the splint condition, oxygen uptake was lower, particularly at higher exercise intensities (67.3 ± 2.3 vs. 70.9 ± 1.5 mL·kg-1·min-1), and ventilation increased during specific rowing protocol steps (1st-4th and 6th). Wearing the splint condition led to changes in rowing technique, including a slower rowing frequency ([18-30] vs. [19-32] cycles·min-1) and a longer propulsive movement ([1.58-1.52] vs. [1.56-1.50] m) than the control condition. The splint condition also had a faster propulsive phase and a prolonged recovery period than the control condition. The splint reduced peak and mean upper body muscle activation, contrasting with an increase in lower body muscle activity, and generated an energetic benefit by reducing exercise cost and increasing rowing economy compared to the control condition. Changing the mandibular position benefited a World-class rower, supporting the potential of wearing an intraoral splint in high-level sports, particularly in rowing.

Effects of Neurodynamics Along With Conventional Exercises on Sciatica Patients: A Single-Blinded Randomized Clinical Trial.

Introduction Sciatica refers to a pain that travels along the course of the sciatic nerve. Patients also often experience paresthesia along with the pain in thighs, which may further radiate to the legs. Most commonly, compression of the lumbosacral nerve root is the cause of this syndrome. Neurodynamics and conventional exercises are considered effective treatment procedures for sciatica. This study aims to find out the efficacy of neurodynamics along with conventional exercises and conventional exercises alone. Methods A total of 58 patients with sciatica aged between 30 and 60 years of both genders were included in the study and randomly divided into a neurodynamic group (n=29) and a conventional group (n=29). Pre-test data were collected before the interventions, and post-test data were collected on the 14th day. The 101 numeric pain rating scale (NPRS) was used to measure data of sciatic pain, the patient-specific functional scale (PSFS) was used to measure the health-related quality of life (HRQL), and a surface electromyography (EMG) biofeedback instrument was used to measure the peak and average muscle activation of the biceps femoris muscle. Results The pre-post data analysis of the neurodynamics and conventional group showed significant (p<0.05) improvement in 101 NPRS, PSFS, and peak EMG values. Insignificant (p>0.05) improvements were seen in average EMG values in the conventional group, and significant (p<0.05) improvement were seen in the neurodynamic group. Between-group analysis showed insignificant (p>0.05) differences in 101 NPRS as well as peak and average EMG values and showed significant (p<0.05) differences in PSFS values. Conclusion Neurodynamics with conventional exercises can help in reducing pain, improving muscle activation of the biceps femoris, and elevating the HRQL of the patient.

Effect of Wearable Passive Back Support Exoskeleton on the Peak Muscle Activation of the Erector Spinae Muscles During Lifting

Effect of Wearable Passive Back Support Exoskeleton on the Peak Muscle Activation of the Erector Spinae Muscles During Lifting

Quadriceps and Hamstrings Activation Peaks Earlier as Athletes Repeatedly Hop, but There are Differences Depending on ACL Reconstruction Technique.

After Anterior Cruciate Ligament Reconstruction (ACLR) athletes face the challenge of regaining their previous competitive level while avoiding re-injury and early knee joint cartilage degeneration. Quadriceps and hamstrings strength reductions and neuromuscular alterations potentially related to risk of re-injury are present after ACLR and relate to deficits in muscle activation. Cross-sectional laboratory study. To examine quadriceps and hamstrings muscle activation during repeated hops in healthy pivoting-sport athletes and those who had undergone ACLR (bone-tendon-bone and semitendinosus graft) who had met functional criteria allowing return to training. Surface electromyography (SEMG) was recorded from vastus medialis and lateralis and medial and lateral hamstrings bilaterally during 30 seconds' repeated hopping in male athletes on average eight months after ACLR surgery (5-12 months). All patients underwent hamstring (HS) (n=24) or bone-tendon-bone (BTB) reconstruction (n=20) and were compared to healthy controls (n=31). The SEMG signals were normalized to those obtained during maximal voluntary isometric contraction. A significant time shift in peak muscle activation (earlier) was seen for: vastus medialis and vastus lateralis activation in the control group, in the BTB group's healthy (but not injured) leg and both legs of the HS group. A significant time shift in peak muscle activation was seen for lateral hamstrings (earlier) in all but the BTB group's injured leg and the medial hamstrings in the control group only. Lower peak activation levels of the vastus lateralis (p\<0.001) and vastus medialis (p\<0.001) were observed in the injured compared to healthy legs and lower peak lateral hamstrings activity (p\<0.009) in the injured leg compared to control leg. Decline in medial hamstring peak activation (p\<0.022) was observed between 1st and 3rd phase of the hop cycle in all groups. Repeated hop testing revealed quadriceps and hamstring activation differences within ACLR athletes, and compared to healthy controls, that would be missed with single hop tests. 3.

Electrical Impedance Tomography for Real-Time Monitoring of Muscle Activity in Robot-Assisted Rehabilitation

This work looks at how Electrical Impedance Tomography (EIT) can be used in robot-assisted rehabilitation to make it easier to watch how muscle activity changes in real time. Quantitative methods are used in this study to look into how well EIT works, including full analyses and comparisons with common tracking methods like Electromyography (EMG). Both EIT and EMG are used to record the participants' mean and peak muscle activation levels as they do a set of Upper Limb, Lower Limb, and Full Body exercises. The study's findings show that EIT is incredibly flexible when it comes to capturing complex patterns of muscle activation across a wide range of rehabilitation routines. Each participant's involvement is shown by different patterns of muscle activation, and these patterns can be seen across different types of exercise. We can learn a lot about how muscles work during rehabilitation by measuring their mean and peak activation levels. This helps us see how well EIT works as a tracking tool. A very important step in validating EIT is to compare it to EMG readings. This shows how consistent and accurate EIT is in real-time monitoring situations. The high level of agreement between the two methods shows that EIT is a reliable alternative to standard monitoring methods, providing an easy to use and non-invasive way to measure muscle activity. The results of this study are even stronger because they include quantitative analyses and a detailed look at system performance data. We carefully check things like signal-to-noise ratio, reconstruction accuracy, and reliability, which shows how strong and dependable the combined EIT system is. These metrics are important for showing how well the system can measure things accurately and reliably in changing rehabilitation situations. This study adds to the growing amount of research on EIT uses in rehabilitation by showing that it can be a useful tool for keeping track of real-time muscle activity. This study opens the door for EIT to be widely used in rehabilitation by showing how muscle activation changes over time and proving its effectiveness against well-known methods. This will eventually lead to better patient outcomes and more effective rehabilitation.

Lightweight active back exosuit reduces muscular effort during an hour-long order picking task

Occupational back exoskeletons and exosuits aim to reduce low back injuries in the workplace. For these technologies to be adopted, it is important that they provide biomechanical benefits to the wearer and do not disrupt job performance. To address this challenge, here we developed a lightweight, soft, active back exosuit that can autonomously control virtual impedance to apply differing assistance during lowering and lifting. In usability tests, participants rated the exosuit as easy to learn and use and reported feeling confident while wearing it. In an experiment involving an hour-long order picking task we demonstrated that the exosuit reduced peak and median muscle activations in the back by 18% and 20%, respectively. Despite the complexity of the movements required, such as walking, bending, and navigating around obstacles while lifting boxes from under a rack, our controller demonstrated impressive robustness with only 14 mistriggers out of 9600 lifts (0.1%). The results of this research suggest that active exosuit technology has the potential to be a highly usable solution to aid warehouse workers in real-world settings.

The acute effects of a stretching and conditioning exercise protocol for the lower limbs on gait performance- a proof of concept and single-blind study.

Due to improvement in movement performance, post-activation performance enhancement (PAPE) may open new possibilities to improve gait performance. However, no study has attempted to translate this phenomenon into walking. Therefore, the study aimed to test whether acute stretching followed by a conditioning exercise can improve subsequent gait performance in healthy adults. Can an exercise protocol subsequently improve gait performance? Sixteen individuals walked four 10-m trials (in each period) before and after 7 min of an exercise protocol composed of stretching (focusing on the lower limb) and a conditioning exercise (standing calf-raise wearing a vest of 20 kg). Gait spatialtemporal parameters and muscle activity of tibialis anterior and gastrocnemius medialis and lateralis muscles were obtained by a 3D-motion system and wireless electromyography, respectively. Before and after the exercise protocol, kinematic and muscle activity parameters were compared by a one-way ANOVA and the Wilcoxon signed-rank test, respectively. After the exercise protocol, the participants walked with a faster step velocity (p < 0.018) and with a lower step duration (p < 0.025). Also, higher peak muscle activity (p < 0.008) and low-frequency (p < 0.034) activation of the anterior tibial muscle after the exercise protocol were observed. In conclusion, the protocol improves the stability and the muscles' efficiency during gait, contributing to a new approach to enhancing gait rehabilitation programs.

Evaluation of a passive arm-support exoskeleton for surgical team members: Results from live surgeries

Background: Musculoskeletal symptoms and injuries adversely impact the health of surgical team members and their performance in the operating room (OR). Though ergonomic risks in surgery are well-recognized, mitigating these risks is especially difficult. In this study, we aimed to assess the impacts of an exoskeleton when used by OR team members during live surgeries. Methods: A commercial passive arm-support exoskeleton was used. One surgical nurse, one attending surgeon, and five surgical trainees participated. Twenty-seven surgeries were completed, 12 with and 15 without the exoskeleton. Upper-body postures and muscle activation levels were measured during the surgeries using inertial measurement units and electromyography sensors, respectively. Postures, muscle activation levels, and self-report metrics were compared between the baseline and exoskeleton conditions using non-parametric tests. Results: Using the exoskeleton significantly decreased the percentage of time in demanding postures (>45° shoulder elevation) for the right shoulder by 7% and decreased peak muscle activation of the left trapezius, right deltoid, and right lumbar erector spinae muscles, by 7%, 8%, and 12%, respectively. No differences were found in perceived effort, and overall scores on usability ranged from “OK” to “excellent.” Conclusions: Arm-support exoskeletons have the potential to assist OR team members in reducing musculoskeletal pain and fatigue indicators. To further increase usability in the OR, however, better methods are needed to identify the surgical tasks for which an exoskeleton is effective.

How to activate the glutes best? Peak muscle activity of acceleration-specific pre-activation and traditional strength training exercises.

Isometric training and pre-activation are proven to enhance acceleration performance. However, traditional strength training exercises do not mirror the acceleration-specific activation patterns of the gluteal muscles, characterized by ipsilateral hip extension during contralateral hip flexion. Therefore, the aim of the study was to determine gluteal muscle activity of acceleration-specific exercises compared to traditional strength training exercises. In a cross-sectional study design, thepeak electromyographic activity of two acceleration-specific exercises was investigated and compared to two traditional strength training exercises each for the gluteus maximus and medius. Twenty-four participants from various athletic backgrounds (13 males, 11 females, 26years, 178cm, 77kg) performed four gluteus maximus [half-kneeling glute squeeze (HKGS), resisted knee split (RKS), hip thrust (HT), split squat (SS)] and four gluteus medius [resisted prone hip abduction (RPHA), isometric clam (IC), side-plank with leg abduction (SP), resisted side-stepping (RSS)] exercises in a randomized order. The RKS (p = 0.011, d = 0.96) and the HKGS (p = 0.064, d = 0.68) elicited higher peak gluteus maximusactivity than the SS with large and moderate effects, respectively. No significant differences (p > 0.05) were found between the HT, RKS and HKGS.The RPHA elicited significantly higher gluteus medius activity with a large effect compared to RSS (p < 0.001, d = 1.41) and a moderate effect relative to the SP (p = 0.002, d = 0.78). The acceleration-specific exercises effectively activate the gluteal muscles for pre-activation and strength training purposes and might help improve horizontal accelerationdue to their direct coordinative transfer.

Vertebral level specific modulation of paraspinal muscle activity based on vestibular signals during walking.

Evoking muscle responses by electrical vestibular stimulation (EVS) may help to understand the contribution of the vestibular system to postural control. Although paraspinal muscles play a role in postural stability, the vestibulo-muscular coupling of these muscles during walking has rarely been studied. This study aimed to investigate how vestibular signals affect paraspinal muscle activity at different vertebral levels during walking with preferred and narrow step width. Sixteen healthy participants were recruited. Participants walked on a treadmill for 8min at 78steps/min and 2.8 km/h, at two different step width, either with or without EVS. Bipolar electromyography was recorded bilaterally from the paraspinal muscles at eight vertebral levels from cervical to lumbar. Coherence, gain, and delay of EVS and EMG responses were determined. Significant EVS-EMG coupling (P < 0.01) was found at ipsilateral and/or contralateral heel strikes. This coupling was mirrored between left and right relative to the midline of the trunk and between the higher and lower vertebral levels, i.e. a peak occurred at ipsilateral heel strike at lower levels, whereas it occurred at contralateral heel strike at higher levels. EVS-EMG coupling only partially coincided with peak muscle activity. EVS-EMG coherence slightly, but not significantly, increased when walking with narrow steps. No significant differences were found in gain and phase between the vertebral levels or step width conditions. In summary, vertebral level specific modulation of paraspinal muscle activity based on vestibular signals might allow a fast, synchronized, and spatially co-ordinated response along the trunk during walking. KEY POINTS: Mediolateral stabilization of gait requires an estimate of the state of the body, which is affected by vestibular afference. During gait, the heavy trunk segment is controlled by phasic paraspinal muscle activity and in rodents the medial and lateral vestibulospinal tracts activate these muscles. To gain insight in vestibulospinal connections in humans and their role in gait, we recorded paraspinal surface EMG of cervicalto lumbar paraspinal muscles, and characterized coherence, gain and delay between EMG and electrical vestibular stimulation, during slow walking. Vestibular stimulation caused phasic, vertebral level specific modulation of paraspinal muscle activity at delays of around 40ms, which was mirrored between left, lower and right, upper vertebral levels. Our results indicate that vestibular afference causesfast, synchronized, and spatially co-ordinated responses of the paraspinal muscles along the trunk, that simultaneously contribute to stabilizing the centre of mass trajectory and to keeping the head upright.

Correlation of 3D Morphometric Changes, Kinematics, and Muscle Activity During Smile.

Knowing the morphological, kinematic, and electrophysiological parameters of the smile in healthy individuals may contribute to evaluating, planning, and monitoring the smile reanimation. This study aimed to determine the correlation between 3D morphometric changes, movement kinematics, and muscle activity in the facial soft tissue of healthy individuals. In this cohort study, 20 volunteers were selected from healthy individuals with no facial disorders. During smiling, three-dimensional face scanning, facial motion capture, and surface electromyography (sEMG) were performed. The average displacement, velocity, and acceleration during facial movements were measured. The mean change in 3D surface morphometry and activation of the zygomaticus major were determined. The volunteers, comprising 10 males and 10 females, had a mean age of 24 ± 10 years; for female, mean age was 23 ± 5 years and for men 26 ± 13 years. Significant correlations were found between kinematic and morphometric data (r = 0.51, p < 0.001), sEMG and morphometric (r = 0.50, p < 0.001) data, and sEMG and kinematic data (r = 0.49, p < 0.002). The maximum acceleration occurred during approximately 65% of the muscle activation time and 64% of the peak muscle activation value. Additionally, the maximum velocity was reached at around 73% of the muscle activation time and 67% of the peak muscle activation value. Furthermore, the maximum displacement values were observed at approximately 88% of the muscle activation time and 76% of the peak muscle activation value. The findings may provide insights into the smile's functional parameters, contribute to understanding facial muscle-related disorders, and aid in improving the diagnosis and treatment of the smile. NA Laryngoscope, 134:3112-3119, 2024.

Treadmill running: how long before soft-tissue vibrations reach a steady state?

The aim of this study was to determine whether a steady state was reached over time in soft-tissue vibrations (STV) when running with different midsole hardness. Kinematics, kinetics and electromyography changes were also investigated in an attempt to be as comprehensive as possible. Forty-five physically active adults (17 females) with experience in treadmill running performed an 8.5 minutes trial at a self-selected speed with soft, medium and hard midsoles. STV of gastrocnemius muscle, kinetics, kinematics and electromyographic activity of gastrocnemius muscle and tibialis anterior were recorded for 30 seconds at minutes 0, 2, 4, 6 and 8. No time effects were found for STV, passive peak, loading rate and leg muscle activity. No significant footwear × time interactions were observed, suggesting that familiarisation is independent of midsole hardness. The fastest adjustments were an increase of foot inversion and active peak within the first 4 minutes respectively before reaching a steady state. Step frequency and vertical stiffness decreased and plateaued at minute 6. Duty factor and contact time increased whereas flight time decreased during the entire running trial. Results indicate that a familiarisation to midsole hardness is not needed for STV reliable measurements. Depending on the other biomechanical parameters assessed, we recommend at least a 6-minute running trial and a longer running trial for contact and flight times assessment.

Relationship Between Knee Frontal Plane Projection Angle and Lower Limb Muscle Activity in Female Athletes.

Anterior cruciate ligament injuries are directly related to the control of dynamic knee valgus in the landing of a jump, and this is mainly due to the correct activation and neuromuscular function of the lower-extremity muscles. The aim of the study is to assess the relationship between lower limb muscle activity during a single-legged drop jump and knee frontal plane projection angle (FPPA). A correlation study. Thirty healthy collegiate female athletes were included in the study. Main outcomes measures were peak knee FPPA and muscle activity (% of maximal voluntary isometric contraction). Peak knee FPPA during a single-legged drop jump test was identified using a 2-dimensional motion analysis system. Muscle activity was assessed using a surface electromyograph for gluteus maximus, gluteus medius, biceps femoris, semitendinosus, vastus medialis quadriceps, vastus lateralis quadriceps, medial gastrocnemius, and lateral gastrocnemius. All variables were assessed for both dominant and nondominant limbs. A correlation analysis between peak knee FPPA and muscle activity was performed. Statistical significance was set at P <.05. A mean peak knee FPPA of 14.52° and 13.38° was identified for dominant and nondominant limb single-legged drop jump test, respectively. Muscle activity (% of maximal voluntary isometric contraction) for muscles assessed ranged from 43.97% to 195.71% during the single-legged drop jump test. The correlation analysis found no significant correlation between any of the muscles assessed and peak knee FPPA during the single-legged drop jump test (Pearson coefficient between -.3 and .1). There is no association between muscle activity from the lower limb muscles and the knee FPPA during a single-legged drop jump in female athletes. Thus, different muscle properties should be assessed in order to understand such an important movement as the knee FPPA during a jump.

Contribution of Trunk Rotation and Abdominal Muscles to Sprint Kayak Performance.

Over the past two decades the importance of trunk contribution to sporting performance has been highlighted through the expanse of literature concerning core stability and strength. However, the role of trunk motion and the abdominal muscles are yet to be established during sprint kayak performance. The purpose of this study was to determine the associations among trunk rotation, kayak velocity, and abdominal muscle activity during on-water sprint kayaking. Eight international paddlers completed five 150 m sprint trials. During each trial peak muscle activation (peak root-mean-squared electromyogram) of the latissimus dorsi, rectus abdominus, external obliques and rectus femoris for ipsilateral (stroke side) and contralateral (opposite side) were recorded as the paddler passed through a 5-m calibrated volume, in conjunction with upper and lower trunk rotation and kayak velocity. Results indicated a significant strong negative relationship between lower trunk rotation and peak velocity (r = -0.684, p < 0.05). Furthermore, a significant strong positive relationship (p < 0.05) with mean velocity was identified for the contralateral rectus abdominus and multiple significant associations between the rectus femoris, rectus abdominus and external obliques during the paddle stroke. Findings indicate that limiting the rotation of the lower trunk will increase both the peak and the mean velocity, with the rectus abdominus, external oblique and rectus femoris combining to assist in this process. Training should therefore focus on developing the strength of these muscle groups to enhance performance.

Validation of a musculoskeletal model for simulating muscle mechanics and energetics during diverse human hopping tasks.

Computational musculoskeletal modelling has emerged as an alternative, less-constrained technique to indirect calorimetry for estimating energy expenditure. However, predictions from modelling tools depend on many assumptions around muscle architecture and function and motor control. Therefore, these tools need to continue to be validated if we are to eventually develop subject-specific simulations that can accurately and reliably model rates of energy consumption for any given task. In this study, we used OpenSim software and experimental motion capture data to simulate muscle activations, muscle fascicle dynamics and whole-body metabolic power across mechanically and energetically disparate hopping tasks, and then evaluated these outputs at a group- and individual-level against experimental electromyography, ultrasound and indirect calorimetry data. Comparing simulated and experimental outcomes, we found weak to strong correlations for peak muscle activations, moderate to strong correlations for absolute fascicle shortening and mean shortening velocity, and strong correlations for gross metabolic power. These correlations tended to be stronger on a group-level rather than individual-level. We encourage the community to use our publicly available dataset from SimTK.org to experiment with different musculoskeletal models, muscle models, metabolic cost models, optimal control policies, modelling tools and algorithms, data filtering etc. with subject-specific simulations being a focal goal.

What differences exist between the lead and trail wrist in extensor carpi ulnaris activity and golf swing joint kinematics in sub-elite golfers?

ABSTRACT This study assessed the lead and trail arm peak and average extensor carpi ulnaris (ECU) muscle activity in association with tri-planar angular velocities of the lead and trail wrists during the golf swing. Fifteen sub-elite, male right-handed golfers (M age = 34.7 years ±13.3, M handicap = 1.5 ± 2.2) were recruited to execute five shots each with their pitching wedge, 7-iron and driver clubs in an indoor golf simulator. Surface electromyography (EMG) sensors were placed over the ECU muscle belly and inertial measurement unit sensors were placed bi-laterally on the distal forearm and dorsum of the hand. There was a statistically greater recruitment of the trail ECU muscle during the downswing (p < 0.001) for all clubs. The lead ECU muscle was recruited more during the backswing (p < 0.001) and follow through (p < 0.024) phases. There were statistically different tri-planar movement patterns between the lead and trail wrist throughout all three phases of the golf swing. No significant relationships were found between downswing EMG data and clubhead kinematics at impact. In conclusion, differing wrist kinematics and associated muscle activity may contribute to the asymmetrical injury pattern seen clinically.

Errors in Augmented Reality Interactions Affected Muscular Loads in the Neck and Shoulders

The use of augmented reality (AR) head-mounted displays is becoming increasingly prevalent due to their ability to provide interactive experiences with high degrees of freedom. However, AR interactions have been shown to be associated with increased biomechanical loads in the neck and shoulders. This repeated-measures study evaluated the effects of interaction errors on neck and shoulder biomechanical loads during AR tasks. Twenty participants performed two standardized AR tasks (omni-directional pointing and cube placing) with and without AR interaction errors. During the tasks, neck and shoulder angles and muscle activity were collected. The results showed that the presence of errors led to increased neck extension and shoulder flexion angles. Peak muscle activity in the shoulders (anterior and medial deltoids) also increased with errors. These findings highlight the importance of reducing interaction errors in AR interfaces to minimize risks of musculoskeletal discomfort and injuries in the neck and shoulders