Anterior-posterior Ground Reaction Forces Research Articles

Does Walking with a Load Affect Asymmetry in Bilateral Lower Extremity Mechanics?

PURPOSE This study sought to analyze the velocity and asymmetry between bilateral lower extremity mechanics according to the load during walking.METHODS A total of 14 adults with right leg dominance participated in this study (Male=7, Female=7). We respectively applied 30% of body weight load carriage on the subjects. Gait characteristics were analyzed with 3-dimensional cinematography and ground reaction force (GRF) system consisted of a center of gravity (COG) velocity, center of pressure (COP) area, leg stiffness, and GRF components.RESULTS Change in velocity of the maximum-minimum COG showed statistically significant in the main effect of load. The 1st anterior-posterior GRF (braking force) and vertical GRF were statistically significant in the main effects of load and bilateral lower limbs. The 2nd anterior-posterior GRF (propulsive force) was statistically significant in the main effect of load. COP area and leg stiffness exhibited statistically significant differences in the main effects of load and bilateral lower limbs. Interaction was observed in the vertical GRF, COP area. Furthermore , one-way variance analysis revealed load main effect had a greater influence on the increase in the magnitude of the vertical GRF and COP area than the asymmetry of bilateral lower limbs.CONCLUSIONS This study revealed the differences in asymmetry between the dominant and non-dominant lower limbs according to the load during walking. These findings may explain the differences shock attenuation and stress mechanisms between the bilateral lower limbs.

Influence of altered torsional stiffness through sole modification of air pressure shoes on lower extremity biomechanical behaviour during side-step cutting maneuvers.

Directional changes in cutting maneuvers are critical in sports, where shoe torsional stiffness (STS) is an important factor. Shoes are designed based on different constructions and movement patterns. Hence, it is unclear how adjustable spacers into the sole constructions of air pressure chambers (APC) affect the STS in side-step cutting. Therefore, this study investigated the effects of altered STS through adjustable sole spacers on ground reaction force (GRF) and ankle and knee joint moments in side-step cutting. Seventeen healthy recreational athletes performed side-step cutting with experimental conditions including (i) barefoot (BF), (ii) unaltered shoes (UAS): soles consisting of APC, and (iii) altered shoes (AS): modified UAS by inserting elastomeric spacers into cavities formed by APC. Mechanical and biomechanical variables were measured. Significant differences were revealed across shoe conditions for impact peak (p = 0.009) and impulse (p = 0.018) in vertical GRF, time to achieve peak braking (p = 0.004), and peak propulsion (p = 0.025) for anterior-posterior GRF in ANOVA test. No significant differences were observed in GRF peaks and impulses between UAS and AS except for a trend of differences in impact peak (p = 0.087) for vertical GRF. At the ankle and knee joint, peak ankle power absorption (p = 0.019), peak knee internal rotation moment (p = 0.042), peak knee extension moment (p = 0.001), peak knee flexion moment (0.000), peak knee power absorption (p = 0.047) showed significant difference across three shoe conditions. However, no significant differences between the UAS and AS were noticed for peak joint moments and power. Altered shoe torsional stiffness did not significantly affect the peak forces and peak ankle and knee joint moments or powers; hence sole adjustment did not influence the cutting performance. This study might be insightful in sports footwear design, and adjusting shoe torsional stiffness by sole modification might be advantageous for athletes playing sports with cutting maneuvers to reduce the risk of injuries by controlling the twisting force at the ankle that frequently happens during cutting maneuvers.

Ground Reaction Forces, Asymmetries and Performance of Change of Direction Tasks in Youth Elite Female Basketball Players.

The magnitude and direction of inter-limb asymmetries in a change of direction (COD) have increased interest in scientific research in recent years. This present study aimed to investigate the magnitude of asymmetries in an elite youth female basketball sample (n = 18, age = 17.79 ± 0.67 y) and determine its directionality using force platform technology. Participants performed 70° and 180° COD tests analyzing the following variables: time, ground contact time (GCT) and ground reaction forces (GRF) along the anterior-posterior, mediolateral, and vertical axes. Inter-limb asymmetries were evident in both COD tests, with substantial differences observed between limbs (p < 0.01). The asymmetry values ranged from 3.02% to 24.31% in COD 180° and from 1.99% to 21.70% in COD 70°, with anterior-posterior GRF consistently exhibiting the highest asymmetry magnitude. Additionally, the directionality exhibited variability between the tests, indicating poor agreement and suggesting the independent directionality of asymmetries across tasks. Moreover, players required more time to complete the COD 180°, the GCT was noticeably longer for the COD 180° than for the COD 70°, and GRF varied across the axis, suggesting that players adapt uniquely to the specific demands of each task. The utilization of force platforms presents a comprehensive approach to assess asymmetries and COD variables performance variables which are "angle-dependent", which could have important implications for COD screening and effective training interventions.

In vivo knee biomechanics during badminton lunges at different distances and different foot positions by using the dual fluoroscopic imaging system.

Background: Lunges are common in badminton. Distance and foot position affect knee joint loadings under lunges, which are closely related to knee injury incidence. Investigations involving dynamic knee motion in vivo, kinetics, and muscle activation in lunges, especially during lunges of different distances and foot positions, are instrumental for understanding knee performance and injury risks of players. Methods: A total of 10 experienced badminton athletes (10 females; height, 164.5 ± 5.0cm; weight, 59.3 ± 6.0kg; and age, 22 ± 1.0years) were recruited. By using a high-speed dual fluoroscopic imaging system, Qualisys motion capture system, Kistler force plate, and Delsys electromyography simultaneously, data were collected during players' 1.5 times leg length lunge, the maximum lunge, and the maximum lunge while the foot rotated externally. Magnetic resonance and dual fluoroscopic imaging techniques were used to analyze the in vivo knee kinematics. Results: Compared with the 1.5 times leg length lunge, knee flexion for the maximum lunge increased significantly (p < 0.05). The anterior-posterior ground reaction force (GRF) and vertical GRF of the maximum lunge were significantly higher than those of the 1.5 times leg length lunge. During the two different foot position lunges with the maximum distance, the posterior translation of knee joint was larger (p < 0.05) when the foot rotated externally than the normal maximum lunge. Moreover, the anterior-posterior GRF and vertical GRF increased significantly when the foot rotated externally. Significant differences were observed in valgus-varus rotation torque and internal-external rotation torque of the knee joint under the two distance lunges and two foot position lunges (p < 0.05). No significant difference was found in knee muscle activation during the two distance lunges and during the two foot position lunges. Conclusion: High knee torque and compressive loadings with increasing lunge distance may cause knee injuries in badminton. When lunging in the external foot rotation under the maximum distance, high quadriceps force and posterior tibia translation force could result in knee injuries among badminton players.

Acute effects of robot-assisted body weight unloading on biomechanical movement patterns during overground walking

Body weight unloading (BWU) is used in rehabilitation/training settings to reduce kinetic requirements, however different BWU methods may be unequally capable of preserving biomechanical movement patterns. Biomechanical analysis of both kinetic and kinematic movement trajectories rather than discrete variables has not previously been performed to describe the effect of BWU on gait patterns during horizontal walking. The aim of the present study was to investigate how robot-assisted BWU producing an dynamic unloading force on the body centre of mass, affects kinematic, kinetic, and spatiotemporal gait parameters in healthy young adults by use of time-continuous analysis. Twenty participants walked overground in a 3-D motion-capture lab at 0, 10, 20, 30, 40, and 50 % BWU at a self-selected speed. Vertical and anterior-posterior ground reaction forces (GRFs) and lower limb internal joint moments were obtained during the stance phase, while joint angles were obtained during entire strides. Time-continuous data were analysed using Statistical Parametric Mapping (SPM) and discrete data using conventional statistics to compare different BWU conditions by means of One-Way Repeated Measures Anova. With increasing BWU, corresponding reductions were observed for GRFs, internal joint moments, joint angles, walking speed, stride/step length and cadence. Observed effects were partially caused by decreased walking speed and increased BWU. While amplitude reductions were observed for kinetic and kinematic variables, trajectory shapes were largely preserved. In conclusion, dynamic robot-assisted BWU enables reduced kinetic requirements without distorting biomechanically normal gait patterns during overground walking in young healthy adults.

Lower Body Joint Moments during the Golf Swing in Older Adults: Comparison to Other Activities of Daily Living.

Golf participation has increased dramatically in the last several years. With this increase in participation, clinicians need better evidenced based strategies to advise those golfers with different pathologies when it is safe to return to the game. Golf teaching professionals also need to understand how to alter golf mechanics to protect injured and/or diseased joints in golfers to allow them to play pain free and avoid further injury. This study used a 3-dimensional link segment model to calculate the net joint moments on the large lower limb joints (knee and hip) during golf (lead and trail leg) and two commonly studied activities of daily living (gait and sit-to-stand) in 22 males, healthy, adult golfers. It also examined the correlations between these knee and hip joint loads and club head speed. The external valgus knee moment and the internal hip adduction moment were greater in the lead leg in golf than in the other activities and were also correlated with club head speed. This indicates a strategy of using the frontal plane GRF moment during the swing. The internal hip extension and knee flexion moment were also greater in the golf swing as compared with the other activities and the hip extension moment was also correlated with club head speed. This emphasizes the importance of hip extensor (i.e., gluteus maximus and hamstring) muscle function in golfers, especially in those emphasizing the use of anterior-posterior ground reaction forces (i.e., the pivoting moment). The golf swing places some loads on the knee and the hip that are much different than the loads during gait and sit-to-stand tasks. Knowledge of these golf swing loads can help both the clinician and golf professional provide better evidence-based advice to golfers in order to keep them healthy and avoid future pain/injury.

Exploratory Investigation Into the Impact of Bilateral and Unilateral Jump Characteristics on Ground Reaction Force Applications in Baseball Pitching.

Lis, R, Szymanski, DJ, Qiao, M, and Crotin, RL. An exploratory investigation into the impact of bilateral and unilateral jump characteristics on ground reaction force applications in baseball pitching. J Strength Cond Res XX(X): 000-000, 2022-Jump tests are effective, valid, and reliable in examining lower-body power that can influence ground reaction forces (GRFs) in baseball pitching. Relationships between drive and stride leg GRFs and fastball velocities while pitching from the wind-up and stretch were evaluated for performance influences across the following conditions: (a) lower-body GRFs from unilateral countermovement jumps (UCMJ) and bilateral countermovement jumps (BCMJ) and (b) BCMJ and drive and stride leg UCMJ height. Nineteen Division I collegiate baseball pitchers (age; 19.9 ± 1.5 years, height; 1.86 ± 0.06 m, body mass; 90.7 ± 13.8 kg) completed BCMJ and UCMJ tests and threw four-seam fastballs from a pitching mound with 2 embedded force plates. Three moderate associations (r ≥ 0.47) were statistically significant (p < 0.05) for BCMJ and UCMJ heights to pitching GRFs. Stride leg UCMJ height was significantly greater than drive leg UCMJ height, p < 0.01, η2 = 0.34. Wind-up and stretch GRFs were statistically similar. Fastball velocities showed a statistically significant association that was moderately high with wind-up and stretch stride leg anterior-posterior GRFs (r ≥ 0.65, p < 0.01). Collegiate pitchers jumped significantly higher with their stride leg, and the sum of vertical unilateral jump height of both legs was significantly greater (27%) than BCMJ height to indicate greater single-leg dominance in jumping. Although stride leg height was higher, improving stride leg jumping performance may be functionally more important in producing greater momentum into foot strike that has the potential to increase fastball velocity.

Effects of cane use on the kinematic and kinetic of lower-extremity joints in inexperienced users

The cane is commonly prescribed for the elderly to maintain balance and enhance independent mobility. However, improper use of cane can increase the risk of falling. Understanding the characteristics of cane gait is critical for better establishing proper cane usage norms. The paper aimed to investigate effects of cane use on kinematics and kinetics of lower extremities in the elderly and the young to guide the development of adaptive cane gait. Twenty participants (10 elder and 10 young) were recruited and walked at a self-comfortable speed or with a cane in a two-point gait. The spatiotemporal gait parameters, hip/knee/ankle joint angles and ground reaction force (GRF) were statistically analyzed using MANOVAs to assess the effects of age and cane. Using the cane significantly decreased step length, cadence and speed and increased step time in both age groups. Age and cane had significant effects on ankle plantarflexion angle in initial swing phase (APA-ISw). In cane gait, the peaks of vertical GRF(V-GRF) and anterior-posterior GRF (AP-GRF) in bilateral lower extremities significantly decreased, and the troughs of right V-GRF significantly increased for both groups. These results suggest that using a cane does interfere with the natural gait of the user and insufficient ankle plantarflexion in initial swing phase (ISw) and reduced AP-GRF may be two key risk factors contributing to cane gait instability. Therefore, the users should consider actively increasing ankle plantarflexion in ISw to avoid deteriorating gait performance due to over-reliance on the cane.

102. An introductory investigation of standing postural control ‘error’ and its relation to balance in adult spinal deformity surgery patients

102. An introductory investigation of standing postural control ‘error’ and its relation to balance in adult spinal deformity surgery patients

Functional Resistance Training Differentially Alters Gait Kinetics After Anterior Cruciate Ligament Reconstruction: A Pilot Study.

Quadriceps weakness is common after anterior cruciate ligament (ACL) reconstruction and can alter gait mechanics. Functional resistance training (FRT) is a novel approach to retraining strength after injury, but it is unclear how it alters gait mechanics. Therefore, we tested how 3 different types of FRT devices: a knee brace resisting extension (unidirectional brace), a knee brace resisting extension and flexion (bidirectional brace), and an elastic band pulling backwards on the ankle (elastic band)-acutely alter gait kinetics in this population. The type of FRT device will affect ground-reaction forces (GRFs) during and after the training. Specifically, the uni- and bidirectional braces will increase GRFs when compared with the elastic band. Crossover study. Level 2. A total of 15 individuals with ACL reconstruction received FRT with each device over 3 separate randomized sessions. During training, participants walked on a treadmill while performing a tracking task with visual feedback. Sessions contained 5 training trials (180 seconds each) with rest between. Vertical and anterior-posterior GRFs were assessed on the ACL-reconstructed leg before, during, and after training. Changes in GRFs were compared across devices using 1-dimensional statistical parametric mapping. Resistance applied via bidirectional brace acutely increased gait kinetics during terminal stance/pre-swing (ie, push-off), while resistance applied via elastic band acutely increased gait kinetics during initial contact/loading (ie, braking). Both braces behaved similarly, but the unidirectional brace was less effective for increasing push-off GRFs. FRT after ACL reconstruction can acutely alter gait kinetics during training. Devices can be applied to selectively alter gait kinetics. However, the long-term effects of FRT after ACL reconstruction with these devices are still unknown. FRT may be applied to alter gait kinetics of the involved limb after ACL reconstruction, depending on the device used.

Gait Improvement in Patients with Knee Osteoarthritis after Proximal Fibular Osteotomy.

Proximal fibula osteotomy (PFO) is a relatively new surgery to treat medial compartment knee osteoarthritis (KOA), which can improve varum deformity and relieve knee joint pain. However, the gait alterations in KOA patients after PFO are still poorly understood. The purpose of this study was to evaluate the gait patterns change in patients of medial compartment KOA after PFO. Gait data were collected for 9 females with unilateral medial compartment KOA before and at 6 months after PFO and also for 9 healthy age-matched females. Paired t-test was used to determine the effect of PFO within the KOA group, and independent t-test were performed to compare between KOA and control groups for spatiotemporal, kinematic, and kinetic variables. The results showed that patients with KOA had significantly increased knee peak flexion angle, knee sagittal range of motion, and peak external hip adduction moment but decreased knee frontal range of motion in the affected limb after PFO. The gait symmetry was improved postoperatively confirmed by single support and swing phases, knee peak flexion angle and sagittal range of motion, peak external hip and knee adduction moments, and peak anterior and peak posterior ground reaction forces. These findings provided evidence of a biomechanical benefit and gait improvement following PFO to treat medial compartment KOA.

Effects of Shoe Lifespan on Gait Kinetics in Women With Knee Genu Varum and Healthy Peers

Background and Aims Knee genu varum is one of the lower limb abnormalities associated with biomechanical changes in lower limbs. The present study aims to compare the effects of shoe lifespan on ground reaction force (GRF) components in women with knee genu varum and healthy peers during running. Methods The is randomized clinical trial. Participants were 15 female college students with knee genu varum and 15 healthy peers. A new pair of sport shoes was given to each participant during to wear them for six months. Then, they were asked to run at a preferred speed in three trials with the new shoes (pre-test phase) and three trials with the used shoes (post-test phase) in a path where a force plate was installed. Statistical analysis was conducted by using repeated measures ANOVA. All analyses were done in SPSS v. 23 software. The significance level was set at 0.05. Results The results indicated the significant main (group) effect of shoes on peak anterior-posterior GRF during heel contact and on the anterior-posterior impulse (P&lt;0.018, d&gt;0.8). The values of these variables in the genu varum group were significantly higher than in the healthy group. Moreover, findings showed the significant main effects of shoes on the time to reach the peak GRF during heel strike and on the loading rate (P&lt; 0.02, d &gt; 0.9). The time to reach the peak GRF during heel strike with the used shoes was shorter than with the new shoes (P= 0.015, d=0.9), while the vertical loading rate during running with the worn shoes was greater than with the new shoes (P=0.019, d=0.9). Conclusion Running with shoes having a lifespan &gt;6 months is a risk factor for women with knee genu varum.

Estimating Running Ground Reaction Forces from Plantar Pressure during Graded Running.

Ground reaction forces (GRFs) describe how runners interact with their surroundings and provide the basis for computing inverse dynamics. Wearable technology can predict time−continuous GRFs during walking and running; however, the majority of GRF predictions examine level ground locomotion. The purpose of this manuscript was to predict vertical and anterior–posterior GRFs across different speeds and slopes. Eighteen recreationally active subjects ran on an instrumented treadmill while we collected GRFs and plantar pressure. Subjects ran on level ground at 2.6, 3.0, 3.4, and 3.8 m/s, six degrees inclined at 2.6, 2.8, and 3.0 m/s, and six degrees declined at 2.6, 2.8, 3.0, and 3.4 m/s. We estimated GRFs using a set of linear models and a recurrent neural network, which used speed, slope, and plantar pressure as inputs. We also tested eliminating speed and slope as inputs. The recurrent neural network outperformed the linear model across all conditions, especially with the prediction of anterior–posterior GRFs. Eliminating speed and slope as model inputs had little effect on performance. We also demonstrate that subject−specific model training can reduce errors from 8% to 3%. With such low errors, researchers can use these wearable−based GRFs to understand running performance or injuries in real−world settings.

The effects of posture on the three-dimensional gait mechanics of human walking in comparison with walking in bipedal chimpanzees.

Humans walk with an upright posture on extended limbs during stance and with a double-peaked vertical ground reaction force. Our closest living relatives, chimpanzees, are facultative bipeds that walk with a crouched posture on flexed, abducted hind limbs and with a single-peaked vertical ground reaction force. Differences in human and bipedal chimpanzee three-dimensional (3D) kinematics have been well quantified, yet it is unclear what the independent effects of using a crouched posture are on 3D gait mechanics for humans, and how they compare with chimpanzees. Understanding the relationships between posture and gait mechanics, with known differences in morphology between species, can help researchers better interpret the effects of trait evolution on bipedal walking. We quantified pelvis and lower limb 3D kinematics and ground reaction forces as humans adopted a series of upright and crouched postures and compared them with data from bipedal chimpanzee walking. Human crouched-posture gait mechanics were more similar to that of bipedal chimpanzee gait than to normal human walking, especially in sagittal plane hip and knee angles. However, there were persistent differences between species, as humans walked with less transverse plane pelvis rotation, less hip abduction, and greater peak anterior-posterior ground reaction force in late stance than chimpanzees. Our results suggest that human crouched-posture walking reproduces only a small subset of the characteristics of 3D kinematics and ground reaction forces of chimpanzee walking, with the remaining differences likely due to the distinct musculoskeletal morphologies of humans and chimpanzees.

The Effects of Corrective Exercise With and Without Visual Feedback on Lower Extremity Biomechanics and Dynamic Balance in Adolescent Female Athletes With Dynamic Knee Valgus: A Pilot Study

Introduction: This study aimed to compare the effectiveness of corrective-plyometric training with and without visual feedback on landing biomechanics and dynamic balance in adolescent female athletes with dynamic knee valgus (DKV).&#x0D; Materials and Methods: A total of 26 adolescent female athletes were randomly divided into feedback (n=10), exercise (n=8), and control (n=8) groups. Six weeks of training with and without visual feedback were prescribed for feedback and exercise groups, respectively. Biomechanical data were measured at initial contact (IC) and maximum knee flexion (MAX) using 8 motion analysis cameras (Vicon) and a Kistler force plate. Y-balance test was employed to evaluate dynamic balance.&#x0D; Results: Based on the between-group outcomes, knee flexion-extension moment at IC (P=0.026), hip internal rotation angle at IC (P=0.016), and MAX (P=0.028) significantly changed during double-leg landing. Ankle dorsiflexion angle (P=0.05), tibial external rotation angle (P=0.012), and anterior-posterior ground reaction force (P=0.05) at IC, maximum tibial external rotation angle between IC to MAX (P=0.042), and hip internal rotation angle at MAX (P=0.022) significantly changed during single-leg landing test. Y-balance significant improvements were recorded in anterior (P=0.000), posteromedial directions (P=0.000), and composite (P=0.023).&#x0D; Conclusion: Corrective-plyometric exercises without visual feedback effectively improve landing biomechanics and dynamic balance in adolescent female athletes with DKV.

Gender Effects on Lower Limb Biomechanics of Novice Runners before and after a 5 km Run

Background: Gender has been considered as an influencing factor in the incidence of sports injuries. But few studies have discussed whether gender differences change after long-distance running. This study aimed at investigating whether the kinematic and ground reaction forces (GRFs) differences between males and females were altered by a 5 km run. Methods: Thirty novice runners (15 males and 15 females) with heel strikes were recruited for this study. In the test before and after the 5 km run, the participants were asked to run through the force plate with their right foot at a speed of 3.3 m/s ± 5%. Kinematics data and GRFs were collected synchronously. Each participant completed five successful running trials for further analysis of data. Results: Gender differences existed in ankle sagittal peak angle (pre: p = 0.059; post: p = 0.013), knee frontal peak angle (pre: p = 0.345; post: p = 0.014), knee horizontal nadir angle (pre: p = 0.056; post: p = 0.005), hip frontal nadir angle (pre: p = 0.103; post: p = 0.001) and peak lateral force (pre: p = 0.564; post: p = 0.001) after a 5 km run, but there were no gender differences before a 5 km run. Gender differences in the knee and hip movement in the frontal plane and horizontal plane and anterior-posterior GRFs changed obviously in the stance phase before and after a 5 km run. Conclusions: The gender difference in lower limb biomechanics during running is not constant. Differences change in peak angle, peak lateral force, knee and hip movement in the frontal plane and horizontal plane, and anterior-posterior GRFs between males and females were associated with the different incidence of running-related injuries, such as patellofemoral joint injuries, anterior cruciate ligament injury and iliotibial band syndrome, etc. These changes can give some concrete details to explore the different incidence rates of lower limb sports injuries between genders.

Lateral Undulation of the Bendable Body of a Gecko-Inspired Robot for Energy-Efficient Inclined Surface Climbing

Sprawling posture animals with their bendable spine, such as salamanders, and geckos, can perform agile and versatile locomotion including walking, swimming, and climbing. Therefore, several roboticists have used them as templates for robot designs to investigate and generate efficient locomotion. Typically, walking and/or swimming abilities are realized by salamander-inspired robots with a bendable body, whereas climbing ability is achieved on gecko-inspired robots with an over-simplified fixed body. In this study, we propose optimal bendable body design with three degrees of freedom (DOFs). Its implementation on a sprawling posture robot is inspired by geckos for climbing enhancement. The robot leg and body movements are coordinated and driven by central pattern generator (CPG)-based neural control. As a consequence, the robot can climb using a combination of trot gait and lateral undulation of the bendable body with a C-shaped standing wave. Through the real robot experiments on a 3D force measuring platform, we demonstrate that, due to the dynamics of the bendable body movement, the robot can gain higher medio-lateral (F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) ground reaction forces (GRFs) at its front legs as well as anterior-posterior (F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> ) GRFs at its hind legs to increase the bending angular momentum (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> ). This results in 52% and 54% reduced energy consumptions during climbing on steeper inclined solid and soft surfaces, respectively, compared to climbing with a fixed body. To this end, the study provides a basis for developing sprawling posture robots with a bendable body and neural control for energy-efficient inclined surface climbing with a possible extension towards agile and versatile locomotion, such as sprawling posture animals.

Ground Reaction Force Differences between Bionic Shoes and Neutral Running Shoes in Recreational Male Runners before and after a 5 km Run.

Running-related injuries are common among runners. Recent studies in footwear have shown that designs of shoes can potentially affect sports performance and risk of injury. Bionic shoes combine the functions of barefoot running and foot protection and incorporate traditional unstable structures based on bionic science. The purpose of this study was to investigate ground reaction force (GRF) differences for a 5 km run and how bionic shoes affect GRFs. Sixteen male recreational runners volunteered to participate in this study and finished two 5 km running sessions (a neutral shoe session and a bionic shoe session). Two-way repeated-measures ANOVAs were performed to determine the differences in GRFs. In the analysis of the footwear conditions of runners, bionic shoes showed significant decreases in vertical impulse, peak propulsive force, propulsive impulse, and contact time, while the braking impulse and vertical instantaneous loading rate (VILR) increased significantly compared to the neutral shoes. Main effects for a 5 km run were also observed at vertical GRFs and anterior–posterior GRFs. The increases of peak vertical impact force, vertical average loading rate (VALR), VILR, peak braking force and braking impulse were observed in post-5 km running trials and a reduction in peak propulsive force and propulsive impulse. The interaction effects existed in VILR and contact time. The results suggest that bionic shoes may benefit runners with decreasing injury risk during running. The findings of the present study may help to understand the effects of footwear design during prolonged running, thereby providing valuable information for reducing the risk of running injuries.

Time-integrated propulsive and braking impulses do not depend on walking speed.

Enhancing propulsion during walking is often a focus in physical therapy for those with impaired gait. However, there is no consensus in the literature for assessing braking and propulsion. Both are typically measured from the anterior-posterior ground reaction force (AP-GRF). While normalization of AP-GRF force by bodyweight is commonly done in the analysis, different methods for AP-GRF time axis normalization are used. Does walking speed affect propulsion and/or braking, and how do different methods for calculating propulsion and braking impact the conclusion, in both healthy adults and those with lower limb impairment? We investigated three different analysis methods for assessing propulsion. 1. BW-TimeIntegration: Bodyweight (BW) normalized time integration of AP-GRF (units of BWs). 2. BW-%StanceIntegration: BW normalized AP-GRF is resampled to percent stance phase prior to integration (units of BW%Stance). 3. BW-Peak: BW normalized peak force (units of BW). We applied these methods to two data sets. One data set included AP-GRFs from trials of slow, self-selected, and fast walking speeds for 203 healthy controls (HCs); a second data set included subjects with lower limb orthopedic injuries. Using the BW-TimeIntegration method, we found no effect of walking speed on propulsion for HCs. Time integration over the longer stance phase of slower walking balanced the lower magnitude AP-GRFs of slower walking, resulting in a time-integrated impulse that was the same regardless of walking speed. In contrast, the other two methods that are not time integration methods found that propulsion increased with walking speed. Similarly, in the gait pathology data set, differences in results were found depending on the analysis method used. For many gait studies concerning propulsion and/or braking, the impulse measure used should be related to the body's change of momentum, necessitating an analysis method with a time integration of the AP-GRF.

The Effect of External Focus Attention Exercise On the Kinetic Risk Factors Associated With ACL Injury

Background and Aims One of the most common and dangerous injuries in sports is an Anterior Cruciate Ligament (ACL) injury. Today, despite the ACL injury prevention programs, the prevalence of this injury remains high. Most of the instructions used in injury prevention programs are based on internal focus, while studies have shown that using external focus can improve performance in individuals. The purpose of this study was to investigate the effect of focus of attention on eight weeks of anterior cruciate ligament injury prevention training on landing skill kinetic variables in soccer players. Methods The current methodology included 35 players from 3 premier league teams in Tehran province. The teams were randomly divided into three groups of Prevent injury and Enhance Performance (PEP) exercises based on the External Focus (EF) (12 people), Internal Focus (IF) (12 people), and control group (11 people). In the pretest of ground reaction force, rate of loading, and time to stabilization during landing skill. The training groups performed pep injury prevention exercises for eight weeks and related instructions instead of warm-up exercises. Control group players were performing the regular activities. ANOVA with repeated measures and one-way ANOVA and Tukey post hoc tests were used to evaluate changes Results The test results showed significant changes in vertical, anterior-posterior ground reaction force and rate of loading in the external focus group (P≤0.05). But there was no critical difference in time to stabilization and internal-external ground reaction force. Conclusion According to the results, external focus instruction has positive effects on kinetic components. Therefore, it is recommended that exercises based on these instructions be used to reduce the risk of ACL injury and to repair this injury.