Horizontal Ground Reaction Forces Research Articles

Single Leg Hop Performance After Anterior Cruciate Ligament Reconstruction: Ready for Landing but Cleared for Take-Off?

While the landing phases of the single-leg hop for distance (SLHD) are commonly assessed, limited work reflects how the take-off phase influences hop performance in patients with anterior cruciate ligament reconstruction (ACLR). To compare trunk and lower extremity biomechanics between individuals with ACLR and matched uninjured controls during take-off of the SLHD. Cross-sectional study design. Laboratory setting. 16 individuals with ACLR and 18 uninjured controls. Normalized quadriceps isokinetic torque, hop distance, and respective limb symmetry indices (LSI) were collected for each participant. Sagittal and frontal kinematics and kinetics of the trunk, hip, knee, and ankle, as well as vertical and horizontal ground reaction forces (GRF) were recorded for loading and propulsion of the take-off phase of the SLHD. Those with ACLR had weaker quadriceps peak torque in the involved limb (p=0.001) and greater strength asymmetry (p<0.001) compared to controls. Normalized hop distance was not statistically different between limbs or between groups (p>0.05) and hop distance symmetry was not different between groups (p>0.05). During loading, the involved limb demonstrated lesser knee flexion angles (p=0.030) and knee power (p=0.007) compared to the uninvolved limb, and lesser knee extension moments compared to the uninvolved limb (p=0.001) and controls (p=0.005). During propulsion, the involved limb demonstrated lesser knee extension moment (p=0.027), knee power (p=0.010), knee (p=0.032) and ankle work (p=0.032), anterior- posterior GRF (p=0.047), and greater knee (p=0.016) abduction excursions compared to the uninvolved limb. Between-limb differences in SLHD take-off suggest a knee underloading strategy in the involved limb. These results provide further evidence that distance covered during SLHD assessment can overestimate function and fail to identify compensatory biomechanical strategies.

Constant low-to-moderate mechanical asymmetries during 800-m track running.

Modifications in asymmetry in response to self-paced efforts have not been thoroughly documented, particularly regarding horizontally-derived ground reaction force variables. We determined the magnitude and range of gait asymmetries during 800 m track running. Eighteen physical education students completed an 800 m self-paced run on a 200 m indoor track. During the run, vertical and horizontal ground reaction forces were measured at a sampling frequency of 500 Hz using a 5 m-long force platform system, with data collected once per lap. The following mechanical variables were determined for two consecutive steps: contact time and duration of braking/push-off phases along with vertical/braking/push-off peak forces and impulses. The group mean asymmetry scores were evaluated using the "symmetry angle" (SA) formula, where scores of 0% and 100% correspond to perfect symmetry and perfect asymmetry, respectively. There was no influence of distance interval on SA scores for any of the nine biomechanical variables (P ≥ 0.095). The SA scores were ∼1%-2% for contact time (1.3 ± 0.5%), peak vertical forces (1.8 ± 0.9%), and vertical impulse (1.7 ± 1.0%). The SA scores were ∼3%-8% for duration of braking (3.6 ± 1.1%) and push-off (3.2 ± 1.4%) phases, peak braking (5.0 ± 2.1%) and push-off (6.9 ± 3.1%) forces as well as braking (7.6 ± 2.3%) and push-off (7.7 ± 3.3%) impulses. The running velocity progressively decreased at 300 m and 500 m compared to that at 100 m but levelled off at 700 m (P < 0.001). There were no modifications in gait asymmetries, as measured at 200-m distance intervals during 800-m track running in physical education students. The 800 m self-paced run did not impose greater mechanical constraints on one side of the body. Experimental procedures for characterizing the gait pattern during 800 m track running could be simplified by collecting leg mechanical data from only one side.

Comparison of ground reaction force and contact time during various-direction lunges between badminton shoes without and with a lateral forefoot wedge sole

This study compared the ground reaction force (GRF), GRF ratio, and contact time between badminton shoes without and with a lateral forefoot wedge sole during lunges in three directions. Fifteen collegiate athletes wore forefoot wedge shoes (5° incline) and control shoes without a lateral forefoot wedge sole (in random order) and performed three typical badminton lunge movements (forward, lateral, and backward directions). A total of nine GRF, GRF ratio, and contact time parameters were analyzed. A paired t test was performed to assess the differences between two shoes. The significance level was set at p &lt; 0.0056 (0.05/9) based on Bonferroni correction to avoid chances of type 1 errors. In the forward lunge, the forefoot wedge shoes resulted in a significantly higher average vertical ground reaction force (GRFv, 3.9%), average horizontal GRF (GRFh, 7.8%) in the braking phase and higher average GRFh (3.9%) in the propulsion phase than the control shoes. In the lateral lunge, the forefoot wedge shoes resulted in a significantly shorter total contact time (−4.6%) than the control shoes in the backward lunge, the forefoot wedge shoes resulted in a significantly higher GRFh to GRFv ratio (6.4%) in the braking phase compared with the control shoes. Thus, shoes with a lateral forefoot wedge sole can effectively enhance mechanical performance in direction changes during forward and backward badminton lunges, and shorter the contact time during lateral badminton lunges. Shoes with a lateral forefoot wedge sole can be considered when designing athletic footwear.

Force plate coverings significantly affect measurement of ground reaction forces.

The purpose of this study was to carry out a material test to investigate the effect of different force plate coverings on vertical and horizontal ground reaction force and derived parameters. Four surface conditions were analysed; bare plate, vinyl, sportflex, and astroturf on a Kistler force plate. Vertical data were collected by dropping a 2 kg rigid, textured medicine ball from a low (61 cm) and a high (139 cm) height. Horizontal data were collected using a custom-built, rigid, metal pendulum device. A one-way ANOVA revealed a significant main effect of surface on peak force and rate of force development for high height, low height, and horizontal force conditions (all p<0.001), with effect sizes in the post-hoc analysis being mostly large to very large. Interestingly, sportflex yielded the highest vertical but the lowest horizontal ground reaction forces. This study showed the use of current force platform coverings had a significant effect on peak force and rate of force development measurements during a standardised testing procedure. Future research should try to obtain rate of force development values that more closely replicate aspects of human performance during standardised testing procedures. Also further investigate the effect of the different surfaces on ground reaction forces during human movement.

Effect of perturbation timing on recovering whole-body angular momentum during very slow walking

Humans prioritize regulation of the whole-body angular momentum (WBAM) during walking. When perturbed, modulations of the moment arm of the ground reaction force (GRF) with respect to the centre of mass (CoM) assist in recovering WBAM. For sagittal-plane perturbations of the WBAM given at toe off right (TOR), horizontal GRF modulations and not centre of pressure (COP) modulations were mainly responsible for these moment arm modulations. In this study, we aimed to find whether the instant of perturbations affects the contributions of the GRF and/or CoP modulations to the moment arm changes, in balance recovery during very slow walking. Perturbations of the WBAM were applied at three different instants of the gait cycle, namely at TOR, mid-swing (MS), and heel strike right (HSR). Forces equal to 16% of the participant’s body weight were applied simultaneously to the pelvis and upper body in opposite directions for a duration of 150 ms. The results showed that the perturbation onset did not significantly affect the GRF moment arm modulation. However, the contribution of both the CoP and GRF modulation to the moment arm changes did change depending on the perturbation instant. After perturbations resulting in a forward pitch of the trunk a larger contribution was present from the CoP modulation when perturbations were given at MS or HSR, compared to perturbations at TOR. After backward pitch perturbations given at MS and HSR the CoP modulation counteracted the moment arm required for WBAM recovery. Therefore a larger contribution from the horizontal GRF was needed to direct the GRF posterior to the CoM and recover WBAM. In conclusion, the onset of WBAM perturbations does not affect the moment arm modulation needed for WBAM recovery, while it does affect the way CoP and GRF modulation contribute to that recovery.

Transition from upright to greater forward lean posture predicts faster acceleration during the run-to-sprint transition.

BackgroundForward body lean and greater horizontal ground reaction force have been associated with being able to accelerate during running. However, kinematic features which may predict acceleration during the run-to-sprint transition have not been determined. The purpose of this study was to determine which kinematic changes occur in recreationally active adults and which kinematic features may predict greater acceleration during the run-to-sprint transition. MethodsForty-seven healthy adults completed straight line running along a 30 m track by running in at ∼4 m.s-1. A minimum of 20 trials were completed, with 25 % triggering a light to signal the participant to accelerate as fast as possible. Step characteristics (velocity, length, duration, cadence) and kinematics (neck, trunk, hip, knee and ankle angles and excursions) were determined using a radar gun and inertial measurement units, respectively. ANOVA was used to determine the step-to-step differences and a multiple linear regression was used to determine the relationship between kinematics and acceleration. ResultsThere was an initial increase in trunk flexion angle during early acceleration (p < 0.001) with knee joint excursion significantly lower (p < 0.001) during loading and propulsion compared to the run-in steps. Greater acceleration was predicted using a stepwise linear regression by five variables including less neck flexion excursion and trunk flexion angle during swing of the 1st step, greater trunk flexion angle and extension excursion of the neck during propulsion of the 2nd step and greater hip flexion angle at foot strike of the 3rd step (r2 =0.804, p < 0.001). SignificanceFaster acceleration was observed when participants transitioned from an upright posture to greater forward trunk lean in the early phase of acceleration. Training the run-to-sprint transition, which was shown to have the greatest increase in velocity over the first 5 m, may be encouraged as a sports specific exercise.

The effect of carbon fiber plated shoes on submaximal running mechanics in non-elite runners

Running shoes constructed with midsole carbon fiber (CF) plates are often worn by elite long-distance runners and may result in mechanical and physiological changes (e.g. increased ground reaction forces, metabolic savings, and speed); however, the effect of these shoes is unknown in a non-elite population. We investigated biomechanical variables in non-elite runners running at submaximal speeds wearing the Nike ZoomX Vaporfly NEXT% 2 shoes (Next%), a shoe with CF plates and specialized energy-returning foam, compared to a shoe without CF plates (Pegasus). 12 male (20.75 ± 0.62 years) and 18 female (22.94 ± 5.06 years) runners were recruited. Following a warmup (400 m) in their own shoes at their preferred pace, runners ran 800 m twice, once in each shoe: Pegasus or Next%. Stride frequency during the shoe trials was controlled (via metronome) to preferred stride frequency recorded in the warmup. Wearable running analysis IMUs were worn to collect data. Stride length was significantly greater (p < 0.000) in Next% (2.97 ± 0.49 m) than in Pegasus (2.85 ± 0.46 m). Horizontal GRF was significantly higher (p = 0.009) in Next% (9.35 ± 1.92 N/kg/s) than in Pegasus (8.72 ± 1.41 N/kg/s). While wearing the Next% shoe, non-elite runners exhibited a significant increase in stride length and horizontal GRF while maintaining a constant stride frequency which ultimately resulted in an increase in running speed.

Walking like a robot: do the ground reaction forces still intersect near one point when humans imitate a humanoid robot?

Bipedal walking while keeping the upper body upright is a complex task. One strategy to cope with this task is to direct the ground reaction forces toward a point above the centre of mass of the whole body, called virtual pivot point (VPP). This behaviour could be observed in various experimental studies for human and animal walking, but not for the humanoid robot LOLA. The question arose whether humans still show a VPP when walking like LOLA. For this purpose, ten participants imitated LOLA in speed, posture, and mass distribution (LOLA-like walking). It could be found that humans do not differ from LOLA in spatio-temporal parameters for the LOLA-like walking, in contrast to upright walking with preferred speed. Eight of the participants show a VPP in all conditions (R2 > 0.90 ± 0.09), while two participants had no VPP for LOLA-like walking (R2 < 0.52). In the latter case, the horizontal ground reaction forces are not balanced around zero in the single support phase, which is presumably the key variable for the absence of the VPP.

Sagittal-plane balance perturbations during very slow walking: Strategies for recovering linear and angular momentum

Spatiotemporal gait characteristics change during very slow walking, a relevant speed considering individuals with movement disorders or using assistive devices. However, we lack insights in how very slow walking affects human balance control. Therefore, we aimed to identify how healthy individuals use balance strategies while walking very slow. Ten healthy participants walked on a treadmill at an average speed of 0.43ms−1, while being perturbed at toe off right by either perturbations of the whole-body linear momentum (WBLM) or angular momentum (WBAM). WBLM perturbations were given by a perturbation on the pelvis in forward or backward direction. The WBAM was perturbed by two simultaneous perturbations in opposite directions on the pelvis and upper body. The given perturbations had magnitudes of 4, 8, 12 and 16% of the participant’s body weight, and lasted for 150ms. After perturbations of the WBLM the centre of pressure placement was modulated using the ankle joint, while keeping the moment arm of the ground reaction force (GRF) with respect to the centre of mass (CoM) small. After the perturbations of the WBAM a quick recovery was initiated, using the hip joint and adjusting the horizontal GRF to create a moment arm with respect to the CoM. These findings suggest no fundamental differences in the use of balance strategies at very slow walking compared to normal speeds. Still as the gait phases last longer, this time was exploited to counteract perturbations in the ongoing gait phase.

Optimization of human gait using singular-value decomposition-based design variables

Age, walking speed, the presence of walking problems, the slope of the ground, and many other parameters affect human gait. Understanding gait variations and obtaining a reference behavior under different conditions is important for identifying abnormal walking behaviors and designing walking assistive devices, orthoses, and prostheses. Predictive dynamics can be used to determine a reference motion for a given task. In the predictive dynamics approach, the motion of a human is generated using design variables, and the equation of motion is considered a constraint. Several design variables were used to generate the motion, and the biological limits of the joints were considered additional constraints in previous studies. A foot-ground contact model was used to generate vertical and horizontal ground reaction forces using the nonlinear spring-damper model. This study proposed a singular value decomposition-based joint angle generation method to reduce the number of design variables and additional constraints. First, the joint angles were calculated using the motion capture data of 225 participants. Then, a joint angle matrix containing the joint angles of all participants in the experiments was created. The modes of the joint angles were extracted using singular-value decomposition. The joint angles were generated by summing the multiplication of the first nine modes of the joint angles and their corresponding design variables. Therefore, the number of design variables was significantly reduced. Moreover, the constraints related to the joint angle limits were intrinsically satisfied. Joint angles, moments, and power were obtained for the optimal energy and moment square cases at different walking speeds. The optimal results were found to be consistent with experimental results in the literature.

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.

Relationship between ground reaction force in horizontal plane and mechanical energy flow in torso during baseball tee batting

ABSTRACT The purpose of this study was to clarify the relationship between the ground reaction force (GRF) in the horizontal plane and the mechanical energy flow in the torso during baseball tee batting. The batting motion and GRF acting on each foot of 30 collegiate baseball players were recorded using a motion capture system and two force plates. To measure the mechanical energy inflow into the torso from both hip joints, the mechanical power of the torso by the force and torque of both hip joints was calculated. The horizontal GRF variables of the stride foot were significantly correlated with mechanical energy inflow into the lower torso from the hip joint of the stride foot side. Conversely, the horizontal GRF variables of the pivot foot were not significantly correlated with mechanical energy inflow into the lower torso from the hip joint of the pivot foot side. Thus, these results suggest that exploring the posture easily to receive the horizontal GRF by the stride foot (i.e., optimisation of magnitude and/or angle of GRF acting on the stride foot) increases the mechanical energy inflow into the lower torso from the hip joint of the stride foot side during baseball batting.

Golf swing in response to anteroposterior ball position

Studies for effective golf coaching such as providing a causal relationship between the address posture and golf-swing behaviors are limited. This study investigated the effects of ball position on golf-swing behaviors. Twenty professional golfers performed golf swing at five different anteroposterior (forward/backward) ball positions: reference ball position (R0) and ±2.14 cm (golf ball radius) and ±4.17 cm (golf ball diameter) to the R0. Their swings were captured using a motion capture system with two force platforms. Statistical parametric mapping was used to compare the ground reaction forces and swing kinematics for different ball positions. The backward (closer to the golfer) ball positions were associated with more extended trunk, knee, and ankle angles in the sagittal plane during the entire golf swing (from address to impact) compared to that of the R0. The backward ball positions were generally associated with decreased horizontal ground reaction forces and pelvis and X-factor angles in the transverse plane during the downswing compared to that of the R0. Whereas, these patterns were reversed for the forward ball positions. These results demonstrate the value of ball position for coaching methods including the importance of a consistent ball position and reveal a consistent human control system for professionals which can provide valuable information for modeling the features of a digitized coaching tool.

Prediction of ground reaction forces using the artificial neural network from capacitive self-sensing values of composite ankle springs for exo-robots

Exoskeleton robots, which are wearable robots that assist human movement, have recently been developed to augment the performance of the human body. In this study, the ankle spring of lower-limb exoskeleton robots was created from a foam core sandwich-structured composite (FCSC) to support the running movement by storing and releasing elastic energy and to predict kinetic data using the self-sensed capacitance data from the structure. Through finite element analysis, the deformation behaviors of the FCSC ankle spring were analyzed and compared with those of a typical fiber-reinforced plastic composite ankle spring. Using a universal test machine, the capacitive-based self-sensing capability of the FCSC ankle spring was examined under several loading rates and cyclic loading. Furthermore, running tests with the lower-limb exoskeleton robot equipped with the FCSC ankle spring were performed on a treadmill. Horizontal and vertical ground reaction forces (GRFs) and capacitance values were obtained from the force plate embedded in the treadmill and FCSC ankle spring, respectively, at various running speeds. These data were used to train an artificial neural network (ANN) model as input and output data. Consequently, the trained ANN model predicted the kinetic data using the capacitance values of the FCSC ankle spring without additional sensors.

Dynamic Postural Stability Is Decreased During the Single-Leg Drop Landing Task in Male Collegiate Soccer Players With Chronic Ankle Instability.

Background:Chronic ankle instability (CAI) is commonly encountered in soccer players. The feelings of instability and anxiety caused by CAI can lead to poor performance, such as difficulty in sharp change of direction during soccer play. The single-leg drop landing (SLDL) task is often used to evaluate dynamic postural stability.Purpose/Hypothesis:The purpose of this study was to clarify whether dynamic stability measured during SLDL is altered in male collegiate soccer players with CAI. The hypothesis was that athletes with CAI would show poor dynamic postural stability.Study Design:Controlled laboratory study.Methods:A total of 103 male collegiate soccer players were recruited, and their limbs were classified based on the new international CAI criteria. All players performed three 5-second SLDL trials on a force plate. The main outcome measures included time to stabilization of the horizontal ground-reaction force (GRF); peak GRF in the vertical, horizontal, and sagittal directions; and trajectory length of the center of pressure during SLDL.Results:Data from 59 CAI limbs and 147 non-CAI limbs were collected in this study. Time to stabilization of horizontal GRF was significantly longer in the CAI limbs (P < .001), and the peak GRFs in all directions were significantly lower in the CAI limbs (vertical, P < .001; horizontal, P < .001; sagittal, P = .001). Additionally, the trajectory length of the center of pressure was significantly greater in the CAI limbs (P = .004).Conclusion:Soccer players with CAI had decreased dynamic postural stability that led them to land softly when performing the SLDL task. Measurement of dynamic postural stability may be useful in the evaluation of CAI.Clinical Relevance:Our findings may be useful for strategies of daily training or as an evaluation tool.

Factor analysis of the biomechanical parameters of pole vault run-up and takeoff: exploring sports performance

ABSTRACT This study aimed to explore a parameter system and build a linear prediction model to effectively and comprehensively evaluate pole vault performance. The Qualisys motion capture system (200 Hz) and three Kistler force platforms (2000 Hz) were used to collect the athletes’ kinematics and ground reaction force data of run-up and takeoff. Finally, 26 biomechanical parameters of 30 successful vaults of eight athletes were analysed by factor analysis, and linear regression analysis was conducted on the extracted factors. Three factors were extracted by factor analysis: F1, F2, and F3. The mean maximum COM height of the 30 vaults was 4.974 m. The score of F2 and F1 increased by 1, and the maximum COM height increased by 0.131 m and 0.112 m, respectively. The F3 did not participate in the prediction of performance. For the training of coaches and athletes, athletes of a higher stature need to expend more effort to achieve a higher training level. Furthermore, improving the speed, mechanical energy, and horizontal propulsion GRF of run-up and takeoff, as well as optimising the force generation strategy of the three lower limb joints in the takeoff support phase, help to achieve a good pole vault performance.

Recovery from sagittal-plane whole body angular momentum perturbations during walking

Healthy individuals highly regulate their whole body angular momentum (WBAM) during walking. Since WBAM regulation is essential in maintaining balance, a better understanding is required on how healthy individuals recover from WBAM perturbations. We therefore studied how healthy individuals recover WBAM in the sagittal plane. WBAM can be regulated by adjusting the moment arm of the ground reaction force (GRF) vector with respect to the whole-body centre of mass (CoM). In principle this can be done by centre of pressure (CoP) modulation and/or adjustments of the GRF direction. Two simultaneous perturbations of the same magnitude were applied in opposite direction to the pelvis and upper body (0.34m apart) to perturb WBAM but not the whole body linear momentum (WBLM), while participants walked on a treadmill. The perturbations were given at toe off right, had a magnitude of 4, 8, 12 and 16% of the participant’s body weight, and lasted for 150ms. A recovery of the WBAM was seen directly after the perturbations, induced by adapting the moment arm of the GRF with respect to the CoM. The hip joint of the stance leg played an important role in achieving the WBAM recovery. A change in the direction of the GRF vector and not a contributing CoP modulation, caused the change in moment arm. However, the change in GRF direction came from a change in the horizontal GRF, which also affects the WBLM. This suggest that regulating WBAM may take precedence over the WBLM in early recovery.

Motion analysis of passive dynamic walking with a rigorously constraint model: A necessary condition for maintaining period-1 gait

The friction force is an important environmental factor that influences dynamic walking. While most of the related works simply assume static friction or Coulomb friction, we use the LuGre friction, which accounts for both static and dynamic effects, to model the horizontal ground reaction force of passive dynamic walking. We present a detailed mathematical modeling method and perform numerical simulations using it. Furthermore, we analyze the ground surface cases of the Coulomb friction condition and static friction condition to verify the model’s generalization. We discover the required condition for the existence of the period-1 gait through investigation. Our mathematical model and theoretical analysis add to our understanding of passive dynamic walking, which helps to positively utilize the natural dynamics of the legged locomotion system in control design.

The mechanical role of the metatarsophalangeal joint in human jumping.

This study investigated the mechanical role of metatarsophalangeal (MTP) joints in human jumping. Eighteen healthy young men performed three types of single-leg jumps (SJ: squat jump; CMJ: countermovement jump; HJ: standing horizontal jump) on a force plate under barefoot (BARE) and forefoot immobilisation (FFIM) conditions. For FFIM, the forefoot was immobilised around the MTP joints of the dominant leg by a custom-made splint. Force-time components and the centre of pressure (COP) trajectory were measured from the ground reaction force (GRF) in the take-off phase of jumping. The vertical jump heights calculated from the net vertical impulse were lower under FFIM than under BARE during the CMJ (p < 0.05). The HJ distance under FFIM was significantly shorter than that under BARE (p < 0.01). The relative net vertical impulse was lower under FFIM than under BARE during the CMJ (p < 0.05). During the HJ, all the horizontal GRF variables were significantly lower under FFIM than under BARE (p < 0.01), but none of the vertical GRF variables differed between the two conditions. The horizontal relative GRF in the 90–95% of the final take-off phase during the HJ was significantly lower under FFIM than under BARE (p < 0.01). Under FFIM, the COP range in the antero-posterior direction in the take-off phase of the HJ decreased (p < 0.05), whereas its range in the anterior direction for the SJ and CMJ increased (p < 0.05). The results of this study indicate that MTP joint motion can play an important role in regulating force-generating capacities of toe flexor muscles in the take-off phase of human jumping, especially in the horizontal direction of horizontal jumping.

The Coupling of Stride Length and Foot Strike in Running.

Modifying stride length and/or foot strike in running results in mechanical alterations associated with injury risk. Stride length and foot strike have often been treated as independent factors that affect running mechanics, but there is evidence to suggest that they may be coupled. The purpose of this study was to determine if foot strike and stride length are coupled in running, and if so, can these variables be independently manipulated? Additionally, we sought to determine how independently and simultaneously manipulating stride length and foot strike influenced running kinematics and kinetics. Fifteen individuals ran over ground with stride lengths +/– 10 % of their preferred stride length while adopting both a fore/mid foot strike and rear foot strike pattern, as well as running with their self-selected stride length and foot strike when the opposite variable was controlled. Three-dimensional motion capture and force plate data were captured synchronously during the manipulated stride length x foot strike trials. The results indicate that foot strike and stride length are coupled, with shorter stride lengths being associated with a F/MFS and longer stride lengths being associated with a RFS pattern. Impact peak magnitude was primarily dependent on foot strike, with a F/MFS pattern reducing the magnitude of the impact peak force regardless of stride length. Peak vertical and horizontal ground reaction forces were found to be primarily dependent on stride length, with longer stride lengths resulting in increased vertical and horizontal ground reaction forces, regardless of foot strike. It is difficult, but possible, to independently manipulate stride length and foot strike. Clinicians should be aware of the coupled changes in stride length and foot strike.