Reaction Force Research Articles

Role of motor unit activity in flexor digitorum brevis to maintain balance during forward leaning

ABSTRACT Our purpose was to compare the influence of motor unit activity in Flexor Digitorum Brevis (FDB) and Soleus (SOL) on force fluctuations during three forward-leaning tasks. Ground reaction forces and high-density EMG signals were collected from 19 males when leaning forward at 25%, 50%, and 75% of maximal forward leaning force. EMG amplitude increased with percent of leaning and was greater for SOL than FDB, but there were no differences in force fluctuations across tasks. Differences in motor unit activity indicated that the relative contribution of the two muscles to the control of balance varied across tasks as confirmed by the association between the fluctuations in neural drive [standard deviation of the filtered cumulative spike train (SD of fCST)] and force [coefficient of variation (CoV) for force]. Specifically, the correlation values were greater for FDB at the lower target forces. Correlation analyses revealed that synaptic noise (CoV for interspike interval) was weakly correlated with the CoV for force, whereas the variability in shared synaptic input (SD of fCST) was strongly correlated with the CoV for force. This finding suggests that the relative influence of the two muscles on the fluctuations in force during forward leaning varied with task requirements.

Influences of footstrike patterns and overground conditions on lower extremity kinematics and kinetics during running: Statistical parametric mapping analysis.

This study investigated lower extremity biomechanics when running on different surfaces among runners with different footstrike patterns. Thirty rearfoot strikers (RFSs) and non-rearfoot strikers (nRFSs) ran at 3.3 m/s on a specially designed indoor track covered with three surfaces: artificial grass, synthetic rubber, and concrete. A motion capture system with ten cameras combined a force plate was used to collect marker trajectory and ground reaction force (GRF) during the running stance phase. A two-way analysis of variance with statistical parametric mapping was employed to evaluate differences in the biomechanics of the lower extremities between footstrike patterns and among running surfaces. The nRFSs exhibited significantly greater ankle inversion angles and increased inversion and internal rotation moments at midstance compared to the RFSs. Conversely, the RFSs demonstrated significantly greater knee abduction moments in late stance. Running on stiffer surfaces was associated with greater vertical GRF in late stance, as well as increased knee and hip extension moments during midstance. Furthermore, running on stiffer surfaces was associated with increased knee abduction moments, hip abduction moments, and hip external rotation moments during late stance. These findings suggested that nRFSs endure more ankle loads, while RFSs face increased knee loads. However, regardless of the footstrike pattern, runners may benefit from selecting softer surfaces to reduce the risk of injury.

The Effect of Repetitive Mechanical Perturbations on Lower Limb Symmetry in Postural Control

Background: Postural symmetry ensures balanced alignment and equal weight distribution, promoting optimal function and minimizing stress on muscles and joints. This study aimed to evaluate lower limb movement symmetry in response to mechanical perturbations. Methods: Twelve healthy young women were subjected to mechanical perturbation tests while standing on the Motek GRAIL system treadmill. Maximum values of kinematic and kinetic parameters and symmetry indices were counted to compare the responses of dominant and non-dominant limbs. Results: The study identified symmetrical and asymmetrical features in lower limb dynamics. Symmetry nearness was observed in the ankle joint angle (SI = 0.03), the hip torque (SI = 0.03), and the vertical component of the ground reaction force (SI = 0.04). However, significant asymmetries were found in the medio-lateral component of the ground reaction force (SI = 1.84), ankle torque (SI = 0.23), knee torque (SI = 0.19), hip angle (SI = 0.15), and knee angle (SI = 0.08). The anterior–posterior component of the ground reaction force (SI = 0.14) showed asymmetry but was not statistically significant. Conclusions: Perturbations impact lower limb dynamics, revealing dominance- and joint-specific asymmetries. Bilateral assessment is crucial for understanding postural control, guiding rehabilitation to restore symmetry, and reducing the risk of injuries, falls, and musculoskeletal strain, particularly in athletes and older adults. These findings emphasize the value of symmetry indices in optimizing therapy and prevention strategies.

Flexural Response of UHPC Wet Joints Subjected to Vibration Load: Experimental and Theoretical Investigation

This study aims to investigate the flexural performance of ultra-high-performance concrete (UHPC) wet joints subjected to vibration load during the early curing period. The parameters investigated included vibration amplitude (1 mm, 3 mm, and 5 mm) and vibration stage (pouring—final setting, pouring—initial setting, and initial setting—final setting). A novel simulated vibration test set-up was developed to reproduce the actual vibration conditions of the joints. The actuator’s reaction force time-history curves for the UHPC joint indicate that the reaction force is stable during the initial setting stage, and it increases linearly with time from the initial setting to the final setting, trending toward stability after 16 h of casting. Under the vibration of 3 Hz-5 mm, cracks measuring 14 cm × 0.2 mm emerge in the UHPC joint. It occurs during the stage from the initial setting to the final setting. The flexural performance of wet joint specimens after vibration was evaluated by the four-point flexural test, focusing on failure modes, load-deflection curves, and the interface opening. The results show that all specimens with joints exhibited bending failure, with cracks predominantly concentrated at the interfaces and the sides of the NC precast segment. The interfacial bond strength was reduced by vibrations of higher amplitude and frequency. Compared with the specimens without vibration, the flexural strength of specimens subjected to the vibration at 3 Hz-3 mm and 3 Hz-5 mm were decreased by 8% and 19%, respectively. However, as the amplitude and frequency decreased, the flexural strength of the specimens showed an increasing trend, as this type of vibration enhanced the compactness of the concrete. Additionally, the calculation model for the flexural strength of UHPC joints has been established, taking into account the impact of live-load vibration. The average ratio of theoretical calculation values to experimental values is 1.01, and the standard deviation is 0.04, the theoretical calculation value is relatively precise.

Relationship Between Vertical Ground Reaction Force and Acceleration from Wearable Inertial Measurement Units During Single-Leg Drop Landing After Anterior Cruciate Ligament Reconstruction

The purpose of this study was to clarify the relationship between vertical ground reaction force (VGRF) and acceleration from wearable inertial measurement units (IMUs) during single-leg drop landing after anterior cruciate ligament reconstruction (ACLR). Twenty-six participants, 42.4 ± 5.3 weeks after ACLR, performed three single-leg drop landing trials bilaterally. The peak VGRF was assessed using a force plate. The resultant acceleration was calculated using IMUs attached to the shank, thigh, and lumbar region. Univariate regression analysis was performed to examine the linear relationship between the VGRF and resultant acceleration. The limb symmetry index (LSI) of the VGRF was linearly associated with the LSI of the resultant accelerations at the shank, thigh, and lumbar sensors (R2 = 0.166, p = 0.039; R2 = 0.525, p < 0.001; and R2 = 0.250, p = 0.009, respectively). In the involved limb, only the resultant acceleration at the thigh was a significant predictor of VGRF (R2 = 0.490, p < 0.001), whereas in the uninvolved limb, the resultant accelerations at the shank, thigh, and lumbar sensors were significant predictors of VGRF (R2 = 0.245, p = 0.010; R2 = 0.684, p < 0.001; and R2 = 0.412, p < 0.001, respectively). Caution may be required when using IMUs to predict VGRF asymmetry because the coefficient of determination for predicting VGRF is lower in the involved limb than in the uninvolved limb.

Modeling and Analysis of the Turning Performance of an Articulated Tracked Vehicle That Considers the Inter-Unit Coupling Forces

The interactions between ground reaction forces and inter-unit coupling forces add complexity to the study of the turning motion of articulated tracked vehicles (ATVs). To accurately analyze the turning performance of an ATV, this study developed a steady-state steering model that captures the effects of load transfer caused by coupling and centrifugal forces. First, based on vehicle kinematics under skidding conditions, formulas that incorporate parameters for the lateral track displacement were derived to calculate the turning radii of the front and rear units. Then, the track traction forces and turning resistance moments were calculated using the shear stress–shear displacement relationship. Finally, a steady-state steering model on firm ground conditions was developed for the vehicle according to mechanical equilibrium conditions, and the model was validated using previously reported data. Analyses of the results revealed that the coupling forces provided the driving moments for the turning motion by the transfer of the centrifugal and ground reaction forces that acted on the front and rear units. During turning, the rear unit had a larger radius than the front unit, and the minimum swept radius of the ATV was dependent upon the radius of the outer track trajectory of the rear unit. Specifically, at a speed of 3.1 m/s and a steering angle of 35°, the vehicle exhibited a minimum outer swept radius of 8.8 m, requiring a turning space equivalent to a 3.1-meter-wide road. The required turning space increased as both the steering angle and speed increased.

Pain-related fear induces aberrant drop jump landing biomechanics in healthy and anterior cruciate ligament reconstructed females.

Rupture of the anterior cruciate ligament (ACL) is a prevalent and debilitating injury typically arising from aberrant biomechanics during landing or deceleration tasks. Pain-related fear, a component of kinesiophobia, has been associated with poor functional outcomes and altered movement patterns in individuals with ACL reconstruction (ACLr), however, the influence of pain-related fear on landing mechanics remains unclear. The purpose of this investigation was to examine the effects of pain-related fear on landing movement patterns in a population of ACLr and healthy females. Thirty-two females (15 recreationally active with a history of ACLr and 17 recreationally active with no history of ACLr) took part. Participants performed five trials of a drop jump (DJ) task (Baseline), underwent a pain stimulus (PS) familiarization task utilizing an electrical stimulus to induce pain-related fear, and performed a subsequent round of DJs while under threat of PS (PS-threat). Lower extremity and trunk kinematics, ground reaction force (GRF) data and muscle activation were analyzed. At baseline, ACLr participants scored higher (21 ± 5.5) on the TSK-11 compared to healthy participants (17 ± 3.4) (p = 0.007). For both groups, the PS intervention significantly increased pain-related fear (ACLr p < 0.001; Healthy p < 0.001). When comparing baseline to PS-threat trials, ACLr participants experienced a significant increase in peak GRF (p = 0.005), decreases in hip (p = 0.003) and knee (p = 0.005) flexion, decreased contact time (p = 0.006) and decreased muscle preactivation for all muscles tested (p < 0.05). Healthy participants experienced significant increases in peak GRF (p = 0.014) and decreased hip (p = 0.005) and trunk peak (p = 0.004) flexion. Pain-related fear alters landing biomechanics in healthy and ACLr females. This may implicate pain-related fear as a contributor to movement alterations commonly associated with ACL injury risk. Level III.

Autologous bone grafting combined with spheroid-based matrix-induced autologous chondrocyte implantation for osteochondral defects of the knee: Good clinical outcomes alongside abnormal postoperative gait patterns.

This study aimed to evaluate the clinical and functional outcomes of autologous bone grafting with spheroid-based matrix-induced autologous chondrocyte implantation (MABCI) for osteochondral defects of the knee by analysing pre- and postoperative patient-reported outcome measures (PROMs). Postoperative gait analysis was conducted and compared with a matched healthy control group to investigate biomechanical deviations. A total of 35 patients (m: 21, f: 14; mean defect size: 4.2 ± 2.4 cm², localisation: femoral condyle: 31, patellofemoral: 5) were analysed. The mean follow-up was 42.6 ± 22.8 months. International Knee Documentation Committee (IKDC), Knee Injury and Osteoarthritis Outcome Score (KOOS), PROMIS 29 profile, and a questionnaire on patient perception of treatment success were assessed to evaluate PROMs. 3D-instrumented gait analysis (GRAIL, Motek) was used to assess lower extremity kinematics, kinetics and vertical ground reaction forces, compared to sex-, age- and body mass index-matched healthy controls. All clinical scores showed significant improvement compared to the preoperative condition (IKDC: 73.1 ± 10.1 vs. 56.6 ± 17.2, p < 0.01; KOOS subcategories: pain 82.0 [±12.7] vs. 70.7 [±16.7] [p < 0.01], symptoms 79.1 [±20.3] vs. 68.9 [±13.9] [p < 0.01], activities of daily living 90.1 [±11.2] vs. 80.5 [±15.6] [p < 0.01], sport and recreational function: 65.3 [±19.3] vs. 51.3 [±26.29] [p < 0.01], quality of life 52.2 [±18.6] vs. 42.6 [±18.6] [p < 0.01]; numeric pain rating scale: 2.7 ± 2.0 vs. 5.0 ± 2.5, p < 0.01). The analysed patients reported a high satisfaction rate (94.3%). Self-selected walking speed was significantly lower than in healthy controls (1.17 ± 0.17 m/s vs. 0.98 ± 0.18 m/s, p < 0.01). Peak knee flexion angle (PKA) during loading response was significantly smaller (9.6° ± 7.0 vs. 17.7° ± 4.6, p < 0.01), and knee extension moment was significantly reduced (0.1 Nm/kg ± 0.2 vs. 0.4 Nm/kg ± 0.2, p < 0.01). MABCI is an effective treatment for osteochondral knee defects, showing significant improvements in all evaluated PROMs. Postoperative gait analysis revealed abnormal gait patterns, including reduced PKA and lower knee extension moment, suggesting a need for further rehabilitation to optimise functional recovery. Level III.

Synthetic data generation in motion analysis: A generative deep learning framework.

Generative deep learning has emerged as a promising data augmentation technique in recent years. This approach becomes particularly valuable in areas such as motion analysis, where it is challenging to collect substantial amounts of data. The objective of the current study is to introduce a data augmentation strategy that relies on a variational autoencoder to generate synthetic data of kinetic and kinematic variables. The kinematic and kinetic variables consist of hip and knee joint angles and moments, respectively, in both sagittal and frontal plane, and ground reaction forces. Statistical parametric mapping (SPM) did not detect significant differences between real and synthetic data for each of the biomechanical variables considered. To further evaluate the effectiveness of this approach, a long-short term model (LSTM) was trained both only on real data (R) and on the combination of real and synthetic data (R&S); the performance of each of these two trained models was then assessed on real test data unseen during training. The principal findings included achieving comparable results in terms of nRMSE when predicting knee joint moments in the frontal (R&S: 9.86% vs R: 10.72%) and sagittal plane (R&S: 9.21% vs R: 9.75%), and hip joint moments in the frontal (R&S: 16.93% vs R: 16.79%) and sagittal plane (R&S: 13.29% vs R: 14.60%). The main novelty of this study lies in introducing an effective data augmentation approach in motion analysis settings.

Prediction of Member Forces of Steel Tubes on the Basis of a Sensor System with the Use of AI

The rapid development of AI (artificial intelligence), sensor technology, high-speed Internet, and cloud computing has demonstrated the potential of data-driven approaches in structural health monitoring (SHM) within the field of structural engineering. Algorithms based on machine learning (ML) models are capable of discerning intricate structural behavioral patterns from real-time data gathered by sensors, thereby offering solutions to engineering quandaries in structural mechanics and SHM. This study presents an innovative approach based on AI and a fiber-reinforced polymer (FRP) double-helix sensor system for the prediction of forces acting on steel tube members in offshore wind turbine support systems; this enables structural health monitoring of the support system. The steel tube as the transitional member and the FRP double helix-sensor system were initially modeled in three dimensions using ABAQUS finite element software. Subsequently, the data obtained from the finite element analysis (FEA) were inputted into a fully connected neural network (FCNN) model, with the objective of establishing a nonlinear mapping relationship between the inputs (strain) and the outputs (reaction force). In the FCNN model, the impact of the number of input variables on the model’s predictive performance is examined through cross-comparison of different combinations and positions of the six sets of input variables. And based on an evaluation of engineering costs and the number of strain sensors, a series of potential combinations of variables are identified for further optimization. Furthermore, the potential variable combinations were optimized using a convolutional neural network (CNN) model, resulting in optimal input variable combinations that achieved the accuracy level of more input variable combinations with fewer sensors. This not only improves the prediction performance of the model but also effectively controls the engineering cost. The model performance was evaluated using several metrics, including R2, MSE, MAE, and SMAPE. The results demonstrated that the CNN model exhibited notable advantages in terms of fitting accuracy and computational efficiency when confronted with a limited data set. To provide further support for practical applications, an interactive graphical user interface (GUI)-based sensor-coupled mechanical prediction system for steel tubes was developed. This system enables engineers to predict the member forces of steel tubes in real time, thereby enhancing the efficiency and accuracy of SHM for offshore wind turbine support systems.

Narrow-based gait in people with Parkinson's disease: Its mechanisms explored

Background People with Parkinson's disease (PD) typically exhibit a narrow-based gait. We previously found that walking with reduced trunk rotation and obliquity led to narrow-based gait in healthy adults; a decrease in trunk motion coincided with a decrease in mediolateral extrapolated center of mass (XCoM) excursion, requiring a smaller step width to maintain a constant mediolateral margin of stability (MoS). Objective To assess whether reduced trunk motion in PD is related to narrow-based gait, without affecting mediolateral MoS. To explore the underlying mechanisms of narrow-based gait, we examined the effects of increasing arm swing (aiming to increase trunk motion), and widening steps on gait in PD. Methods Fifteen people with PD and narrow-based gait and 17 age-matched controls walked on a treadmill for three minutes at a fixed gait speed during three conditions: baseline, increased arm swing and widened step width. Step width, trunk rotation and obliquity were calculated using marker data, and XCoM excursion and MoS using ground reaction forces. Results Trunk rotation, XCoM excursion, and step width were significantly smaller in PD compared to controls, while the MoS did not differ. Increased arm swing did not substantially increase trunk motions in PD, though people with PD were able to widen their step width. Conclusions We provide further evidence for a relation between trunk motion and step width. In PD, reduced trunk motion may contribute to narrow-based gait, without affecting mediolateral MoS; future work is needed to confirm a causal relationship between reduced trunk motion and narrow-based gait in PD.

Punch Force Classification using K Means and a Data Logging System

Much research has been conducted worldwide on the recognition and monitoring of punches in martial art sports during the training process. The performance of the punching movements can be accurately analyzed based on the collected data. The current study aims to classify the punches on a punching bag using K Means based on a data logging system. Its stages are hardware design, hardware implementation, hardware testing, learning, and testing. The FSR 402 sensor was used to measure the punching force. GY6500 MPU6500 was also utilized to identify and measure the reaction force of these punches. The data were collected utilizing K Means and were subsequently tested. The results revealed that the system exhibited good performance, proven by its accuracy of 93.6%, precision of 0.933, recall of 0.934, and F1 score of 0.934. Based on these results, it seems that the classification of right and left punch forces can be efficiently carried out. This system can help users analyze the punching bag training process, and thus improve their performance.

Patients with Achilles tendinopathy use compensation strategies to reduce tendon load during rehabilitation exercises

BackgroundThis study aimed to determine differences in the Achilles tendon loading during rehabilitation exercises for Achilles tendinopathy and the ranking of these exercises, based on load, in patients with tendinopathy and controls. MethodsSixteen patients with Achilles Tendinopathy (5F & 11 M, 44.1 ± 12.9 yr) and sixteen controls (4F & 12 M, 39.4 ± 15.6 yr) performed rehabilitation exercises while 3D motion and ground reaction forces were measured. Musculoskeletal modeling was used to compute joint kinematics and estimate Achilles tendon load by summing the forces of individual triceps surae muscles. Subsequently, peak Achilles tendon loading, loading impulse, loading rate, loading indexes (a combination of the previous parameters), and joint angles at the time of peak loading were determined and compared between patients and controls. FindingsPatients with tendinopathy exhibited significantly reduced peak Achilles tendon loading compared to controls during the exercises with the highest peak loading: unilateral heel drop with flexed knee (3.66 ± 0.90BW [AT] vs. 4.65 ± 1.10BW [Control], p = 0.003, d = 0.979) and walking (3.37 ± 0.49BW [AT] vs. 3.68 ± 0.33BW [Control], p = 0.044, d = 0.742). Additionally, during the heel drop exercise, patients with tendinopathy showed reduced ankle dorsiflexion and knee flexion. The ranking of exercises by peak loading or loading index was similar for both groups but varied depending on which loading parameter was used to define Achilles tendon loading. InterpretationDuring the highest load-imposing exercises, patients with tendinopathy employ compensatory strategies to reduce the load on their Achilles tendon. Clear instructions and feedback on the patient's performance are crucial as altered exercise execution influences Achilles tendon loading.

Relationship between volleyball spike jump height and lower limb kinetics is stronger for orientation leg than rear leg

ABSTRACT The orientation and rear legs have different roles in the spike jump (SPJ) in volleyball, yet the relationship between the jump height and kinetics of each leg remains underexplored. We aimed to clarify the relationships between jump height and kinetics of the orientation and rear legs in the SPJ. This study included 18 female college volleyball players. The experimental trial comprised an SPJ with a three-step run-up. The motion and ground reaction forces were measured using eight high-speed cameras and two force plates. Kinetic variables from the last foot contact to take-off were calculated, and their relationship with jumping height was examined. The results showed that the peak joint torques for ankle plantar flexion (r = 0.562, p = 0.015), hip extension (r = 0.684, p = 0.002), and hip abduction (r = 0.670, p = 0.002) of the orientation leg were significantly positively correlated with jump height. No significant correlations were found for the rear leg, except for the hip abduction torque (r = 0.538, p = 0.021). These findings indicate that interindividual difference in jump height are more strongly related to the kinetics of the orientation leg than those of the rear leg after final rear foot contact.

Application of Wearable Insole Sensors in In-Place Running: Estimating Lower Limb Load Using Machine Learning

Musculoskeletal injuries induced by high-intensity and repetitive physical activities represent one of the primary health concerns in the fields of public fitness and sports. Musculoskeletal injuries, often resulting from unscientific training practices, are particularly prevalent, with the tibia being especially vulnerable to fatigue-related damage. Current tibial load monitoring methods rely mainly on laboratory equipment and wearable devices, but datasets combining both sources are limited due to experimental complexities and signal synchronization challenges. Moreover, wearable-based algorithms often fail to capture deep signal features, hindering early detection and prevention of tibial fatigue injuries. In this study, we simultaneously collected data from laboratory equipment and wearable insole sensors during in-place running by volunteers, creating a dataset named WearLab-Leg. Based on this dataset, we developed a machine learning model integrating Temporal Convolutional Network (TCN) and Transformer modules to estimate vertical ground reaction force (vGRF) and tibia bone force (TBF) using insole pressure signals. Our model’s architecture effectively combines the advantages of local deep feature extraction and global modeling, and further introduces the Weight-MSELoss function to improve peak prediction performance. As a result, the model achieved a normalized root mean square error (NRMSE) of 7.33% for vGRF prediction and 10.64% for TBF prediction. Our dataset and proposed model offer a convenient solution for biomechanical monitoring in athletes and patients, providing reliable data and technical support for early warnings of fatigue-induced injuries.

Symmetries of the vertical ground reaction force, contact time and area, and center of pressure during gait in female patients 3weeks post-total hip arthroplasty.

Few studies have assessed vertical ground reaction force, contact time, contact area, and center of pressure during gait in the early phase post-total hip arthroplasty. This study aimed to investigate whether these parameters are more pronounced in participants post-total hip arthroplasty compared to healthy controls. We included 22 female participants who underwent total hip arthroplasty (age, 68.9±7.2years; body mass index, 22.9±2.6kg/m2) and 11 healthy female controls (age, 50.3±7.8years; body mass index, 19.4±1.7kg/m2) as controls. Vertical ground reaction force, contact time, contact area, and center of pressure during gait were measured using a force plate. Comparisons between the affected, unaffected, and control legs were conducted using one-way analysis of variance or the Kruskal-Wallis test, with additional comparisons using independent t-tests or the Mann-Whitney U test. The first peak force was lower, the time to the first peak force and heel contact time were longer, and the contact area at the second peak force was significantly larger in the affected leg than in the unaffected leg or the right leg of the controls. These parameters were significantly more asymmetrical in the total hip arthroplasty cohort compared to the controls, with significant differences in the starting position and center of pressure length. The loading timing, magnitude, and form of plantar contact during gait were more asymmetrical in the total hip arthroplasty cohort than in healthy females. Early-phase rehabilitation post-total hip arthroplasty should address these asymmetries.

Acute effects of voluntary breathing patterns on postural control during walking.

Breathing and postural control is reported to be both neuromuscularly and mechanically interdependent. To date, the effects of voluntary abdominal and thoracic breathing (VAB and VTB) on the EMG activity of muscles involved in both respiratory and postural functions, as well as gait biomechanics related to these breathing patterns, have not been investigated in young, healthy adults. The aim of the study was to evaluate the EMG responses of neck and trunk muscles, as well as the kinematic, stability, and kinetic parameters of gait induced by VAB and VTB compared to involuntary breathing (INB). Twenty-four healthy, physically active participants (12 men and 12 females) were required to complete three two-minute walking sessions on an instrumented treadmill (e.g. devices with capacitive sensors embedded beneath the running belt) at 5.0kmh-1, first with INB and then alternatively with VAB and VTB. A respiratory inductive plethysmography unit was used to provide real-time visual feedback of the breathing pattern performed by each participant. The EMG activity of the sternocleidomastoid (SCM), upper trapezius (UT), thoracic and lumbar erector spinae (TES and LES), as well as spatiotemporal (step width, stride length, stride time, stance phase, swing phase, and cadence), stability (anteroposterior and mediolateral center of pressure trajectory), and dynamic gait parameters (vertical ground reaction forces, vGRF) were recorded during each testing condition. Our findings revealed that both voluntary breathing patterns significantly affected the EMG activity of the SCM (p<0.01) and UT (p<0.05), with the activity between these muscles, as expressed by the SCM:UT ratio, being more balanced during VAB (0.94) and VTB (1.05) compared to INB (0.73). Additionally, VAB walking led to a narrower step width (p<0.01) and reduced vGRF over the forefoot (p<0.01) compared to INB walking. Neither VAB nor VTB influenced the activation levels of the LES and TES, nor did they affect other spatiotemporal, stability, or dynamic gait parameters (p>0.05). Our findings suggest that certain gait parameters (e.g. step width, forefoot vGRFs) are primarily influenced by VAB compared to INB, likely due to the more balanced activation of the SCM and UT muscles. This balanced activation may enhance head stability and control during walking, thereby contributing to improved postural control.

The Effects of Speed on the Running Performance of a Small Two-Wheeled Lunar Rover

Small wheeled lunar rovers tend to dig into surfaces via wheel rotation, causing them to slip and get stuck on regolith. Additionally, reducing power consumption remains a longstanding challenge. This study created a small two-wheeled rover and conducted tests at various wheel rotation speeds to assess the effects of rotation speed on its running performance. Through running tests and the measurement of reaction force, the influence of different wheel rotation speeds on running performance was clarified. Running at low rotation speeds prevented slipping and sinking. Additionally, the amount of sinkage was shown to converge to a certain level even at higher rotation speeds. These findings suggest that the maximum wheel rotation speed at which the rover avoids getting stuck allows the rover to achieve running with low-power consumption.

Effect of a tailored exercise programme on kinematics and kinetic knee injury risk during different side-cutting

ABSTRACT Despite the high incidence of knee injuries reported in non-professional sports, the implementation of specific training programmes aimed at mitigating the kinematic and kinetic factors associated with these injuries remains limited. To determine the effects of a tailored exercise programme on kinematic and kinetic variables during side-cutting activities. Fifty-seven physically active participants were randomised into control group (CG; n: 28) that received no intervention, and an experimental group (EG; n: 29), that performed an individualised exercise programme that included a combination of strength, neuromuscular, proprioceptive, eccentric training and whole-body vibration (WBV) exercises. Knee, hip and trunk angles, vertical ground reaction force (VGRF), force in the antero-posterior (AP) and medio-lateral (ML) axes, acceleration, contact time and impulse were assessed during three types of side-cutting, two open manoeuvres (30º and 45º – SC30 and SC45 –respectively) and one closed manoeuvre (45º – SC45cl-). After the 12-week intervention, EG participants had lower knee extension during all side-cuttings, shorter contact time and lower acceleration, VGRF and impulse compared to CG during side-cutting manoeuvres. A tailored exercise programme could be an effective neuromuscular and biomechanical strategy to reduce risk factors for knee injury in healthy, physically active young people.

Associations between force-velocity-power profile in sprinting and ballistic lower limb tests in adolescent elite footballers

ABSTRACT This study investigated the relationships between performance and force-velocity (F-v) parameters obtained from a ballistic lower limb (BLL) and a 30-m sprint test in 24 adolescent elite footballers (13.2–15.1 years old). In the BLL test, normal ground reaction force and velocity were recorded by two force plates and a linear encoder, respectively, and take-off velocity (vto) at 0% of body mass was considered as performance. In the 30-m sprint test, raw velocity-time data were measured using a radar, and 5, 10 and 30 m sprint times using a timing gate system. Theoretical maximal force (F 0), velocity (v 0) and power (P max) were determined using the Samozino’s method. All sprint times were significantly correlated with vto (p = 0.004 to p < 0.001; −0.57 to −0.72), but no significant correlation was found between the respective F-v parameters ;(p = 0.152 to 0.913). As both tests assess explosive performance, players who can produce a high vto will also perform best in short sprints. However, the F-v discrepancies highlight the complementarity of these tests: the BLL test minimises the coordination and technical influences that can affect sprint performance in adolescents.