Maximum Ground Reaction Force Research Articles

Impact of hindlimb length variation on jumping dynamics in the Longshanks mouse.

Distantly related mammals (e.g. jerboa, tarsiers, kangaroos) have convergently evolved elongated hindlimbs relative to body size. Limb elongation is hypothesized to make these species more effective jumpers by increasing their kinetic energy output (through greater forces or acceleration distances), thereby increasing take-off velocity and jump distance. This hypothesis, however, has rarely been tested at the population level, where natural selection operates. We examined the relationship between limb length, muscular traits and dynamics using Longshanks mice, which were selectively bred over 22 generations for longer tibiae. Longshanks mice have approximately 15% longer tibiae and 10% longer femora compared with random-bred Control mice from the same genetic background. We collected in vivo measures of locomotor kinematics and force production, in combination with behavioral data and muscle morphology, to examine how changes in bone and muscle structure observed in Longshanks mice affect their hindlimb dynamics during jumping and clambering. Longshanks mice achieved higher mean and maximum lunge-jump heights than Control mice. When jumping to a standardized height (14 cm), Longshanks mice had lower maximum ground reaction forces, prolonged contact times and greater impulses, without significant differences in average force, power or whole-body velocity. While Longshanks mice have longer plantarflexor muscle bodies and tendons than Control mice, there were no consistent differences in muscular cross-sectional area or overall muscle volume; improved lunge-jumping performance in Longshanks mice is not accomplished by simply possessing larger muscles. Independent of other morphological or behavioral changes, our results point to the benefit of longer hindlimbs for performing dynamic locomotion.

Shoe choice may affect fencing lunge attack performance.

The purpose of this study was to investigate the differences in attack time and lower limb biomechanics when performing fencing lunge with fencing shoes (FS) and commonly used court shoes (CS). Additionally, the study aimed to evaluate whether fencing shoes with a heel cup (FSH) could reduce lower limb impact. Thirteen female collegiate fencers who had participated in national-level competitions were recruited for this study. Participants performed the lunge on a human-shaped target while wearing FS, FSH, or CS in a randomized order. Biomechanical data were collected using a 3D motion analysis system synchronized with a force plate. A signal light, and an accelerometer were attached to the target's head to initiate lunge movement and detect hit moment for calculating attack time. Attack time was significantly shorter when wearing FS (0.92 ± 0.05s) and FSH (0.93 ± 0.07s) compared to CS (0.96 ± 0.06s). The maximum angular velocity of ankle plantarflexion in rear foot push-off phase was significantly slower when wearing FS and FSH than when wearing CS. The maximum knee posterior shear force, maximum knee flexion moment, and maximum ankle medial shear force during the front foot step phase were significantly greater when wearing FS than when wearing CS. These forces were significantly reduced or nearly significantly reduced when wearing FSH, and there were no significant differences compared to wearing CS. The maximum ankle medial shear force during the push-off phase in rear foot was the greatest when wearing FS but decreased significantly when using FSH. However, this force was still greater than when wearing CS. Wearing FS resulted in a higher loading rate (LR) on the front foot. This LR was reduced when a heel cup was used but still remained higher than when wearing CS. There were no significant differences in the forward extension of body, maximum ground reaction force, or center of pressure displacement during front foot step and rear foot push-off phases among the three shoe conditions. Wearing FS can enhance lunge performance, and the use of a heel cup can effectively reduce lower limb impact.

Reducing Limb Asymmetry in Females Collegiate Basketball: A Randomized Trial

Background and Aim:  Interlimb strength asymmetry has garnered significant attention in the field of sports science for its potential to influence both athletic performance and injury risk. Despite this, there is a noticeable gap in the literature concerning its impact on elite female collegiate basketball players. The study aims to assess the effectiveness of targeted weaker limb strength training in reducing jump strength asymmetry among elite female college basketball players. Materials and Methods: A randomized controlled design was used, involving 24 elite female college basketball players from Guangzhou Sports University. The Experimental Group underwent specialized training for the weaker limb, while the Control Group followed balanced training. The primary outcome was the change in the maximum ground reaction force (GRF) during single-leg jumps. Linear Mixed-Effects models were used for statistical analysis, with a two-tailed significance level of p<0.05. Result: The intervention was effective in reducing Countermovement Jump Asymmetry and Horizontal Jump Asymmetry with statistical significance (p-values 0.0045 and 0.029, respectively) but did not significantly impact Lateral Jump Asymmetry (p-value 0.2733). These findings were consistent when comparing the Experimental and Control groups post-intervention (p-values 0.0055 and 0.0474 for Countermovement and Horizontal, respectively; 0.3995 for Lateral). Time and group interaction analyses were significant but not universally consistent across all measures after the Bonferroni correction. Overall, the intervention had a mixed but generally positive effect on jump asymmetry. Conclusion: The study demonstrates that targeted weaker limb strength training can effectively reduce jump strength asymmetry in elite female collegiate basketball players. These findings have implications for athletic training regimens aimed at both improving performance and reducing the risk of injury.

Impact of Injury Prevention Video Feedback on Biomechanical Variables of the Knee Joint during Cutting Maneuver

PURPOSE This study aims to analyze the effects of injury prevention video feedback on kinetic variables of the knee joint during the cutting maneuver.METHODS Twenty-eight healthy men participated and motion and force data were collected using infrared cameras, a force plate, and a Witty timing system. Paired t-tests were employed for data evaluation using the SPSS 26.0 program.RESULTS Results showed increased abduction and lateral rotation angles of the knee joint at the lower height of the center of mass (COM) (p<. 05). The lateral rotation of the knee joint decreased at initial ground contact (p<.05). Flexion angular velocity increased at initial ground contact after video feedback (p<.05) and decreased at the lower height of COM (p<.05). Abduction angular velocity decreased at the lower height of COM (p<.05), and internal rotation angular velocity was increased on the initial ground contact (p<.05). Maximum ground reaction force for anterior-posterior and medial-lateral directions increased after video feedback (p<.05). Flexion and internal rotation moments increased, and adduction moment also increased (p<.05).CONCLUSIONS In conclusion , video feedback effectively reduced knee load during the cutting maneuver, contributing to injury prevention for the knee joint.

무릎 신전근 피로 수준이 외발 드롭 착지 시 무릎 관절 안정성에 미치는 영향

This study was to investigate the effect of experimentally induced knee extensor muscle fatigue on biomechanical variables related to knee stability during landing after a drop jump. Methods: A total of 14 young men participated voluntarily. As for the fatigue induction method, isokinetic equipment (Biodex System 4, Biodex Medical Systems, Inc. USA) was used, Kinematic data of the lower limbs were collected using a 3D Motion Analysis Eagle system (EVART 4.6, Santa Rosa, CA, USA) connected to 12 cameras at a sampling rate of 200 Hz, and ground reaction forces were obtained using an AMTI OR6-5 force platform (Watertown, MA, USA) was used to collect at a sampling rate of 1200 Hz. Results: The maximum knee flexion angle during one-leg drop landing was significantly increased after fatigue induction than before fatigue induction, but there was no significant difference among the fatigue induction conditions in knee valgus and varus, lateral rotation and medial rotation during one-leg drop landing. The shear stress in the tibia showed a tendency to increase according to the level of fatigue, but no significant difference was found. On the other hand, in the sagittal plane, the maximum knee joint moment was significantly decreased after fatigue induction, and the maximum ground reaction force was also found to be significantly decreased in the condition after fatigue induction compared to the condition before fatigue induction. Conclusion: Fatigue of the knee joint extensors following the fatigue protocol did not lead to significant changes in biomechanical variables related to knee stability. However, there was a significant decrease in maximum knee joint moment and maximum ground reaction force, and a significant increase in maximum knee joint angle during one-leg drop landing after fatigue induction. Therefore, the results of the study demonstrated that local fatigue (knee extensor fatigue exercise) according to the fatigue protocol did not affect biomechanical variables related to knee stability, but did affect biomechanical variables related to task performance.

The Effect of Muscles Fatigue on the Knee’s Kinetics and Kinematics Characteristics

Badminton is very popular on college campuses. In badminton, the anterior cruciate ligament of the players has a higher risk of injury. There are many studies investigating the impact of fatigue on the injury of professional athletes, but few studies focused on college students. We hypothesized that the knee joint would experience greater ground reaction forces, valgus moments, and flexion moments of lunge contact in amateur after fatigue than those indicators before fatigue. Ten male badminton amateurs were enrolled in this study. They performed a lunge to hit the shuttlecock at the designated position and then quickly returned to the starting position before and after fatigue. Fatigue was induced by repeated isokinetic flexion/extension of the knee. Lower body kinematics and ground reaction force (GRF) were collected and further used to calculate the lower body joint moments from initial contact to maximum knee flexion. Compared to the pre-fatigue condition, the peak flexion moment (p = 0.012) and peak abduction moment of knee joint (p = 0.01), and maximum horizontal ground reaction force (p = 0.027) increased significantly at the initial contact (p = 0.01). After muscle fatigue, the knee buckling moment and valgus moment increased significantly at initial contact, and the horizontal backward maximum GRF also increased significantly. These changes might increase the injury risk of anterior cruciate ligament (ACL). The fatigue of the muscles around the knee joint did not change the maximum GRF in the vertical direction at the moment of contact. Combined with the results of our study, badminton coaches and teachers should increase the training of lower extremity muscle strength and endurance in our daily class and training, and also should pay special attention to the coordinated development of muscles.

드롭 랜딩 시 팔의 위치에 따른 발레 무용수들의 하지분절 충격흡수 전략 차이

Purpose: The purpose of this study is to investigate the difference rthough analysis of kinematic and kinetics variables to determine how ballet dancers absorb the impact on the human body during drop landing to minimize injury.BR Method: Twelve female ballerinas in their twenties (age: 21.83±1.85 years, height: 161.82±4.86㎝, weight: 51.47±6.55㎏, experience: 9.67±2.77 years old) who were familiar with jumping and landing movements were studied. To analyze the motion of the lower extremity for the drop landing motion, a 3D motion analysis was performed using 18 infrared cameras (Qualasiys7+, SWE), and the ground reaction force was obtained using a ground reaction force measuring device (Kistler 9287BA).BR Results: The results of this study are as follows. 1) There was a stisatically significant difference in the maximum and minimum angles of the hip joint during single-leg rdop landing according to the position of the arm (p＜.05). 2) There was a statistically significant difference in the range of motion of the hip joint during single-leg drop landing according to the position of th earm (p＜.05). 3) There was a statistically significant difference in ankle angular velocity during single-leg drop landing according to the position of the arm (p＜.05). 4) There was no statistically significant difference in the amount of change in the moment of the lower extremity joint during single-leg drop landing according to the position of the arm (p＞.05). 5) There was no statistically significant difference in the maximum ground reaction force value during singleleg drop landing according to the position of the arm (p＞.05).BR Conclusion: Therefore, as a result of this study, there was no differenc ein both feet during one drop landing depending on the position of the arm, and it seems that the ballet dancer makes a stable landing by increasing the flexion movement of the hip joint.

Physiotherapy skills in the difference of years of therapists’ experience and affiliations

In Japan, a physiotherapist is considered to be ‘experienced’ and having sufficient time in the field, regardless of their level, efficacy, or quality of training, after five years of practice. However, this definition is insufficient for establishing quality and uniformity among physiotherapists in Japan. The purpose of this study was to establish the groundwork for standardisation in education and evaluation. It aimed to evaluate physiotherapy skills by means of a Weight Shift (WS) practical assessment task. Participants of this study included 10 physiotherapists from two institutions. The WS task was repeated three times on a simulated patient. The ground reaction force (GRF) of the simulated patient was recorded during the task. The ratio of the centre of pressure (COP) displacement was calculated by dividing the COP displacement by the distance between the centre of pressure of both feet of the simulated patient to normalise. Correlational statistical analysis was used to confirm whether years of experience changes the degree of WS. The obtained data was compared between the institutions of therapists. The results of this study confirm that the correlation between the data obtained and years of therapists’ experience is weak or absent. There were significant differences between each institution’s ratios for COP displacement as well as for the maximum GRF. It was considered that years of therapists’ experience does not necessarily correlate with physiotherapy skill, especially if participants had six or more years of experience. Greater differences were observed between institutions with regards to the characteristics of physiotherapy skill.

Effects of Leg Stiffness Regulated by Different Landing Styles on Vertical Drop Jump Performance.

The purpose of this study was to investigate the effects of stiffness regulated by landing styles on drop jump performance. Twenty-four male lacrosse athletes performed drop jumps with stiff (ST), self-selected (SS), and soft (SF) landing from a 0.42 m box. Leg stiffness, ground contact time, depth, jump height, maximum ground reaction force (GRF), GRF at the start of the propulsive phase, mean power, peak power, and the reactive strength index (RSI) were calculated. The results showed that jump height and the RSI had strong correlations to power production in all drop jump styles. Power would be a key factor to overall athletic performance. Repeated measures ANOVA showed significant differences (p < 0.05) in all variables among the three styles. Drop jumps with SS landing had comparable jump height to drop jumps with SF landing and power output to drop jumps with ST landing. Drop jumps with ST landing had significantly lower jump height, but higher GRF, power, and the RSI compared to drop jumps with SF landing. In drop jump testing, drop jumps with SS landing should be used if power and jump height were the major concerns; if the RSI was the major concern, drop jumps with ST landing should be used. Training with drop jumps, one of the main objectives should be increasing power output due to its significant correlation to jump height and the RSI in all conditions.

Adaptive locomotion: Foot strike pattern and limb mechanical stiffness while running over an obstacle

Previous studies of level running suggest runners adjust foot strike to control leg stiffness. This study aimed to determine how runners adjusted mechanical stiffness and foot strike prior to, during, and after a drop in surface height. Ten healthy subjects (5 male, 5 female; 24.32 ± 5.0 years) were video recorded as they ran on an outdoor path with a single drop in surface height (12.5 cm). Foot strike was recorded, while subject velocity, duty factor (DF), normalized maximum ground reaction force (GRFbw), vertical hip displacement (Δy), leg compression (ΔL), vertical (Kvert) and leg stiffness (Kleg), touchdown (TD) and takeoff angle (TO), and flight (Tf) and contact time (Tc) were calculated. Compared to the step before the drop, Tf, GRFbw, Kvert, Kleg, and TO increased, while Tc, DF, Δy, ΔL, and TD decreased in the step after the drop. Across trials, runners had either consistent or variable foot strike patterns. Runners using a consistent pattern most often shifted from rear to fore-foot strike in the steps before and after the drop, while those with a variable pattern showed less dramatic shifts. All parameters, except TD, were significantly different (p < 0.04) based on foot strike pattern, and comparisons between steps before and after the drop (except TD) were significantly different (p < 0.004). Runners with a variable foot strike pattern experienced smaller shifts within mechanical parameters when traveling over the drop, suggesting these runners may be able to stabilize limb mechanics on interrupted surfaces.

뇌전도와 운동역학적 분석을 통한 대학운동선수들의 재부상 불안의 타당성 검증

This study was conducted to evaluate the re-injury anxiety of athletes who have experienced injuries through EEG and kinesiology experiments. For 35 college athletes, the frontal-alpha asymmetry(FAS), load factor during drop landing, anteroposterior, left and right, vertical maximum ground reaction force, and required time were measured through EEG, and correlation analysis between group differences and variables was performed. the following conclusions were drawn.BR First, there was no difference in the amount of FAS change between the normal group and the injured group. Second, the lording rate of the injured group was high during drop landing, so the cause of injury was high. Third, the amount of FAS change had a negative effect on the maximum left and right ground reaction force.BR In conclusion, the hypothesis that “the risk of injury will increase due to reinjury anxiety even if the muscle function and pain of the lower extremities of the injured group are similar to those of the normal group” was partially verified.

A 3D-Printed Sole Design Bioinspired by Cat Paw Pad and Triply Periodic Minimal Surface for Improving Paratrooper Landing Protection.

Paratroopers are highly susceptible to lower extremity impact injuries during landing. To reduce the ground reaction force (GRF), inspired by the cat paw pad and triply periodic minimal surface (TPMS), a novel type of bionic cushion sole for paratrooper boots was designed and fabricated by additive manufacturing. A shear thickening fluid (STF) was used to mimic the unique adipose tissue with viscoelastic behavior found in cat paw pads, which is formed by a dermal layer encompassing a subcutaneous layer and acts as the primary energy dissipation mechanism for attenuating ground impact. Based on uniaxial compression tests using four typical types of cubic TPMS specimens, TPMSs with Gyroid and Diamond topologies were chosen to fill the midsole. The quasi-static and dynamic mechanical behaviors of the bionic sole were investigated by quasi-static compression tests and drop hammer tests, respectively. Then, drop landing tests at heights of 40 cm and 80 cm were performed on five kinds of soles to assess the cushioning capacity and compare them with standard paratrooper boots and sports shoes. The results showed that sports shoes had the highest cushioning capacity at a height of 40 cm, whereas at a height of 80 cm, the sole with a 1.5 mm thick Gyroid configuration and STF filling could reduce the maximum peak GRF by 15.5% when compared to standard paratrooper boots. The present work has implications for the design of novel bioinspired soles for reducing impact force.

Machine learning and statistical prediction of fastball velocity with biomechanical predictors

In recent years, one of the most important factors for success among baseball pitchers is fastball velocity. The purpose of this study was to (1) to develop statistical and machine learning models of fastball velocity, (2) to identify the strongest predictors of fastball velocity, and (3) to compare the models' prediction performances. Three dimensional biomechanical analyses were performed on high school (n = 165) and college (n = 62) baseball pitchers. A total of 16 kinetic and kinematic predictors from the entire pitching sequence were included in regression and machine learning models. All models were internally validated through ten-fold cross-validation. Model performance was evaluated through root mean square error (RMSE) and calibration with 95% confidence intervals. Gradient boosting machines demonstrated the best prediction performance [RMSE: 0.34; Calibration: 1.00 (95% CI: 0.999, 1.001)], while regression demonstrated the greatest prediction error [RMSE: 2.49; Calibration: 1.00 (95% CI: 0.85, 1.15)]. Maximum elbow extension velocity (relative influence: 19.3%), maximum humeral rotation velocity (9.6%), maximum lead leg ground reaction force resultant (9.1%), trunk forward flexion at release (7.9%), time difference of maximum pelvis rotation velocity and maximum trunk rotation velocity (7.8%) demonstrated the greatest influence on pitch velocity. Gradient boosting machines demonstrated better calibration and reduced RMSE compared to regression. The influence of lead leg ground reaction force resultant and trunk and arm kinematics on pitch velocity demonstrates the interdependent relationship of the entire kinetic chain during the pitching motion. Coaches, players, and performance professionals should focus on the identified metrics when designing pitch velocity improvement programs.

Development of a screening formula for sarcopenia using ground reaction force during sit-to-stand motion

BackgroundGround reaction force during sit-to-stand motion is related to lower extremity strength, and such measurements indicating weak muscle strength, may be linked to sarcopenia. We aimed to examine and describe the relationship between sarcopenia and ground reaction force during sit-to-stand motion to develop a diagnostic tool. Research questionCan ground reaction force during sit-to-stand motion help detect sarcopenia? MethodsThis study included 627 community-dwelling older adults who were divided into non-sarcopenia and sarcopenia groups to compare ground reaction force parameters. A sit-to-stand force analyzer was used to measure the ground reaction force, power, and time between the minimum and maximum ground reaction force. We assessed the association between sarcopenia and each ground reaction force parameter. Receiver operating characteristic curve analysis was performed with sarcopenia as the dependent variable and ground reaction force-related measurements as independent variables. The probability of predicting sarcopenia was calculated using multiple logistic regression analysis, with sex and age as independent variables, and another receiver operating characteristic analysis was performed using the probability value. ResultsGround reaction force parameters related to strength and power were lower in the sarcopenia group than in the non-sarcopenia group. Furthermore, we were able to develop a formula to detect sarcopenia using the maximum ground reaction force (area under the curve; 0.906 [95% CI 0.858–0.954] for men and 0.858 [0.808–0.908] for women). The sensitivity and specificity of sarcopenia detection using this formula were 89.7% and 80.5%, respectively, for men and 95.0% and 60.9%, respectively, for women. SignificanceGround reaction force during sit-to-stand motion may reflect low skeletal muscle strength associated with sarcopenia. We were able to develop a method for sarcopenia detection by analyzing the sit-to-stand force required in only one or two sit-to-stand motions, even though it does not measure the skeletal muscle mass directly.

ACUTE EFFECT OF WHOLE-BODY VIBRATION COMBINED WITH STATIC STRETCHING ON FEMALE GYMNASTS’ LEG AND VERTICAL STIFFNESS DURING RUNNING

&lt;p&gt;Although whole-body vibration (WBV) combined with static stretching (SS) have proven a suitable method to enhance flexibility without losing muscular strength, it is still unknown what its effect are on running mechanics. Therefore, the purpose of the study was to examine the effect of a WBV combined with SS (WBVSS) warm up procedure on lower limb stiffness and spatiotemporal variables during running. Twenty-two female gymnasts performed 30-s running bouts at 4.44 m.s-1 on a treadmill before and after a WBVSS intervention stimulus. The WBVSS stimulus included two sets of 20s of SS of four different muscle groups on the vibration platform. Leg and vertical stiffness values were calculated using a spring mass model. The results showed a statistically significant interaction effect on vertical stiffness (Kvert), leg stiffness (Kleg), change in leg length (ΔL), maximal ground reaction force (Fmax), contact time (Tc), and flight time (Tf). Results indicated that, a warm-up including SS combined with WBV did not produce significant effect on mean values of Kleg and Kvert, and related kinetic and kinematic variables.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;&lt;p&gt;&lt;strong&gt; Article visualizations:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;img src="/-counters-/edu_01/0994/a.php" alt="Hit counter" /&gt;&lt;/p&gt;

Immediate Effect of Valgus Knee Brace and Lateral Wedge Insole on Gait Parameters in Medial Compartment Osteoarthritis of Knee: A Cross-sectional Study

Introduction: Orthoses have been reported to improve function and symptom reduction in knee Osteoarthritis (OA) of the medial compartment. Biomechanical changes introduced instantly in the gait with the use of orthoses can be evaluated to understand their effectiveness. Aim: To determine and compare the immediate effect of valgus knee brace and Lateral Wedge Insole (LWI) on gait parameters in medial compartment OA knee patients. Materials and Methods: This was a cross-sectional study conducted in the Department of Physical Medicine and Rehabilitation at a tertiary centre from August 2018 to July 2019. A 56 patients of knee OA (Kellgren-Lawrence system grades 2 or 3) were assessed by instrumented gait analysis before and just after orthotic fitment. Gait parameters related to External Knee Adduction Moment (EKAM) (e.g., maximum Ground Reaction Force (mGRF), vertical Ground Reaction Forces (vGRF), Varus Angle (VA) were assessed via motion capture during walking, in all four conditions: barefoot (B), LWI, valgus Knee brace (KB), Combined (C) i.e., (LW+KB). Statistical analysis was done using International Business Machines (IBM) Statistical Package for Social Sciences (SPSS) version 24.0. To find the significant difference in given parameters, repeated measure Analysis of Variance (ANOVA) was applied taking p-value &lt;0.05. Results: A total of 56 patients (13 men, 43 women) mean age of 58.04±5.8 years and a mean Body Mass Index (BMI) of 27.4±3.5 kg/m2 were analysed. A 35 patients had OA grade 2 and 21 were classified as grade 3. No significant difference in mean vGRF and VA values was found among LW, KB and C (p=0.118) and (p=0.894) throughout the stance phase. The significant difference was in mean mGRF values during initial stance phase (0-20% of gait cycle) (p=0.036). Conclusion: The orthoses may not swiftly provide beneficial biomechanical changes in gait parameters of medial OA knee patients.

Acute Effects of Whole-Body Vibration Warm-up on Leg and Vertical Stiffness During Running.

Paradisis, GP, Pappas, P, Dallas, G, Zacharogiannis, E, Rossi, J, and Lapole, T. Acute effects of whole-body vibration warm-up on leg and vertical stiffness during running. J Strength Cond Res 35(9): 2433-2438, 2021-Although whole-body vibration (WBV) has been suggested as a suitable and efficient alternative to the classic warm-up routines, it is still unknown how this may impact running mechanics. Therefore, the aim of this study was to investigate the effect of a WBV warm-up procedure on lower-limb stiffness and other spatiotemporal variables during running at submaximal speed. Twenty-two males performed 30-second running bouts at 4.44 m·s-1 on a treadmill before and after a WBV and control warm-up protocols. The WBV protocol (vibration frequency: 50 Hz, peak-to-peak displacement: 4 mm) consisted of 10 sets of 30-second dynamic squatting exercises with 30-second rest periods within sets. Leg and vertical stiffness values were calculated using the spring mass model. The results indicated significant increases only after the WBV protocol for leg stiffness (3.4%), maximal ground reaction force (1.9%), and flight time (4.7%). Consequently, the WBV warm-up protocol produced a change in running mechanics, suggesting a shift toward a more aerial pattern. The functional significance of such WBV-induced changes needs further investigation to clearly determine whether it may influence running economy and peak velocity.

Optimization-based subject-specific planar human vertical jumping prediction: Effect of elbow flexion and weighted vest.

Jumping strategies differ considerably depending on athletes' physical activity demands. In general, the jumping motion is desired to have excellent performance and low injury risk. Both of these outcomes can be achieved by modifying athletes' jumping and landing mechanics. This paper presents a consecutive study on the optimization-based subject-specific planar human vertical jumping to test different loading conditions (weighted vest) during jumping with or without elbow flexion during the arm-swing based on the validated prediction model in the first part of this study. The sagittal plane skeletal model simulates the weighting, unweighting, breaking, propulsion phases and considers four loading conditions: 0%, 5%, 10%, and 15% body weight. Results show that the maximum ground reaction forces, the body center of mass position, and velocities at the take-off instant are different for different loading conditions and with/without elbow flexion. The optimization formulation is solved using MATLAB® with 35 design variables with 197 nonlinear constraints for a five-segment body model and 42 design variables with 227 nonlinear constraints for a six-segment body model. Both models are computationally efficient, and they can predict ground reaction forces, the body center of mass position, and velocity. This work is novel in the sense that presents a simulation model capable of considering different external loading conditions and the effect of elbow flexion during arm swing.

Validation of the wearable sensor system - MoveSole® smart insoles

Biomechanical analysis of gait is commonly used in physiotherapy. Ground reaction forces during phases of gait is one element of kinetic analysis. In this article, we analyze if the MoveSole® smart insole is valid and accurate equipment for measuring ground reaction forces in clinical physiotherapy. MoveSole® StepLab is a mobile measurement system for instant underfoot force measurements during gait. Unique electromagnetic film (EMFI) based sensor technology and printed electronics production technology is integrated in the MoveSole® StepLab measurement system. The MoveSole® StepLab measures plantar ground reaction force distribution over the sensors and provides an estimation of the maximum total ground reaction force. We developed a two phase validation process to extract relevant parameters and compared the results to a Kistler force plate using the BioWare® analyzing program as a reference method. Our results show that MoveSole® smart insoles reach the strong level of accuracy needed in clinical work concerning highest ground reaction forces during step (Pearson correlation .822 - .875). The correlation of the time when the maximum ground reaction force occurred was moderate, e.g. during heel strike or toe-off (Pearson correlation natural gait speed .351 - .462, maximum gait speed .430). Our conclusion is that MoveSole® smart insoles are a potential tool for analyzing and monitoring gait ground reaction forces during physiotherapy processes.

중학교 하키 우수선수와 비우수선수의 페널티 스트로크 동작에 대한 운동역학적 비교분석

The purpose of this study was to kinetics comparative analysis on penalty stroke motion of excellent and non-excellent hockey athletes in middle school. This study was concluded as follows. First, there was no significant difference in the time required for the penalty stroke movement of excellent and non-excellent athletes in all phases. Second, there was no significant difference in COM(center of mass) displacement during penalty stroke motions of excellent and non-excellent players. Third, there was no significant difference in COM horizontal velocity during penalty stroke motions of excellent and non-excellent athletes. Fourth, the stick head velocity during the penalty stroke motion of the excellent and non-excellent athletes showed a significant difference at impact, and the excellent athletes were found to be fast (p<.05). Fifth, there was a significant difference in the torsion angle of the trunk during the penalty stroke motion of the excellent and non-excellent athletes in Event 1 (p<.05). Sixth, the maximum torso torsioning angular velocity during penalty stroke motions of excellent and non-excellent athletes showed a significant difference in phase 2, and non-excellent athletes were found to be fast (p<.05). Seventh, the maximum GRF(ground reaction force) in the penalty stroke motion of the excellent and non-excellent athletes showed a significant difference in the forward foot, and the excellent athletes showed great strength (p<.05).