Comparison of fMRI coregistration results between human experts and software solutions in patients and healthy subjects

Functional magnetic resonance imaging (fMRI) performed by echo-planar imaging (EPI) is often highly distorted, and it is therefore necessary to coregister the functional to undistorted anatomical images, especially for clinical applications. This pilot study provides an evaluation of human and automatic coregistration results in the human motor cortex of normal and pathological brains. Ten healthy right-handed subjects and ten right-handed patients performed simple right hand movements during fMRI. A reference point chosen at a characteristic anatomical location within the fMRI sensorimotor activations was transferred to the high resolution anatomical MRI images by three human fMRI experts and by three automatic coregistration programs. The 3D distance between the median localizations of experts and programs was calculated and compared between patients and healthy subjects. Results show that fMRI localization on anatomical images was better with the experts than software in 70% of the cases and that software performance was worse for patients than healthy subjects (unpaired t-test: P = 0.040). With 45.6 mm the maximum disagreement between experts and software was quite large. The inter-rater consistency was better for the fMRI experts compared to the coregistration programs (ANOVA: P = 0.003). We conclude that results of automatic coregistration should be evaluated carefully, especially in case of clinical application.     

Quantification of inertial sensor-based 3D joint angle measurement accuracy using an instrumented gimbal

This study quantified the accuracy of inertial sensors in 3D anatomical joint angle measurement with respect to an instrumented gimbal. The gimbal rotated about three axes and directly measured the angles in the ISB recommended knee joint coordinate system. Through the use of sensor attachment devices physically fixed to the gimbal, the joint angle estimation error due to sensor attachment (the inaccuracy of the sensor attachment matrix) was essentially eliminated, leaving only error due to the inertial sensors. The angle estimation error (RMSE) corresponding to the sensor was found to be 3.20° in flexion/extension, 3.42° in abduction/adduction and 2.88° in internal/external rotation. Bland-Altman means of maximum absolute value were -1.63° inflexion/extension, 3.22° in abduction/adduction and -2.61° in internal/external rotation. The magnitude of the errors reported in this study imply that even under ideal conditions irreproducible in human gait studies, inertial angle measurement will be subject to errors of a few degrees. Conversely, the reported errors are smaller than those reported previously in human gait studies, which suggest that the sensor attachment is also significant source of error in inertial gait measurement. The proposed apparatus and methodology could be used to quantify the performance of different sensor systems and orientation estimation algorithms, and to verify experimental protocols before human experimentation.     

Effect of walking speed during gait in water of healthy elderly

BackgroundWalking in water (WW) is frequently used as an aquatic exercise in rehabilitation programs for the elderly. Understanding gait characteristics of WW is of primary importance to effectively design specific water-based rehabilitation programs. Moreover, as walking speed in water is reduced with a possible effect on gait parameters, the age- and environment-related changes during WW have to be investigated considering the effects of instantaneous walking speed. Research question: how do gait kinematic characteristics differ in healthy elderly between WW and on land walking condition (LW)? Do elderly show different walking patterns compared to young adults? Can these kinematic changes be accounted only by the different environment/age or are they also related to walking speed?MethodsNine healthy elderly participants (73.5 ± 5.8 years) were acquired during walking in WW and LW at two different speeds. Kinematic parameters were assessed with waterproofed inertial magnetic sensors using a validated protocol. The influence of environment, age and walking speed on gait parameters was investigated with linear mixed models.ResultsShorter stride distances and longer stride durations were observed in WW compared to LW. In the sagittal plane, hip and knee joint showed larger flexion in WW (>10deg over the whole stride and ∼28deg at foot strike, respectively). Furthermore, lower walking speeds and stride distances were observed in elderly compared to young adults. In the sagittal plane, a slightly more flexed hip joint and a less plantarflexed ankle joint (∼9 deg) were observed in the elderly. Significance: The results showed the importance of assessing the walking speed during WW, as gait parameters can vary not only for the effect environment but also due to different walking speeds.     

Sagittal plane translation of the knee during stair walking in healthy volunteers measured by an electrogoniometer chain

Maximal sagittal plane knee translation during stair walking was investigated in 5 healthy male subjects without any previous history of knee joint trauma during 2 types of ascents and descents (straight and side) using an electrogoniometer system (CA-4000, OS Inc., Hayward CA, USA). During the ascents, the tibia moved anteriorly in relation to femur, whereas during the descents it moved posteriorly. The maximum translations occurred within the range of 39° to 51° of knee flexion and were significantly larger during the ascents than during descents, but there was no difference between straight and side activities. There were significant interindividual differences in the maximum translations during the ascent or descent cycles but no differences between trials or the right or left limbs. The mean difference between repeated trials was 1.2 mm and the 95% confidence interval was ±0.6 mm.     

Comparison of point and two-dimensional shear wave elastography of the spleen in healthy subjects

BACKGROUNDFew systematic comparative studies of the different methods of physical elastography of the spleen are currently available.AIMTo compare point shear wave and two-dimensional elastography of the spleen considering the anatomical location (upper, hilar, and lower pole).METHODSAs part of a prospective clinical study, healthy volunteers were examined for splenic elasticity using four different ultrasound devices between May 2015 and April 2017. The devices used for point shear wave elastography were from Siemens (S 3000) and Philips (Epiq 7), and those used for two-dimensional shear wave elastography were from GE (Logiq E9) and Toshiba (Aplio 500). In addition, two different software versions (5.0 and 6.0) were evaluated for the Toshiba ultrasound device (Aplio 500). The study consisted of three arms: A, B, and C.RESULTSIn study arm A, 200 subjects were evaluated (78 males and 122 females, mean age 27.9 ± 8.1 years). In study arm B, 113 subjects were evaluated (38 men and 75 women, mean age 26.0 ± 6.3 years). In study arm C, 44 subjects were enrolled. A significant correlation of the shear wave velocities at the upper third of the spleen (r = 0.33088, P < 0.0001) was demonstrated only for the Philips Epiq 7 device compared to the Siemens Acuson S 3000. In comparisons of the other ultrasound devices (GE, Siemens, Toshiba), no comparable results could be obtained for any anatomical position of the spleen. The influencing factors age, gender, and body mass index did not show a clear correlation with the measured shear wave velocities.CONCLUSIONThe absolute values of the shear wave elastography measurements of the spleen and the two different elastography methods are not comparable between different manufacturers or models.     

99mTc-DTPA clearance measured by a dual head gamma camera in healthy subjects and patients with sarcoidosis

^99mTc-DTPA clearance was studied in ten healthy non smokers, five asymptomatic smokers and nine non smoking patients with sarcoidosis in the supine position with a dual head gamma camera allowing simultaneous information of regional clearance rates in frontal and dorsal projections. In the patients with sarcoidosis, a bronchoalveolar lavage was performed prior to the clearance study. DTPA clearance rate was measured during 60–90 min and data were corrected for recirculating radioactivity. The coefficients of variation for measurements on 2 consecutive days in the 10 healthy non smokers were 9%–11% for the right and left lung, anterior and posterior projections. The T_1/2 calculated from total lung projections were 90–92 min for the anterior view and 84–85 min for the posterior view. Regional measurements did not add further information. No apico-basal difference was found but there was a significant fronto-dorsal gradient in^99mTc-DTPA clearance in the supine position. Smokers had significantly (P<0.01) faster clearance rates (T_1/2 28±10 min) than healthy controls. In the sarcoidosis group clearance rates were increased in four patients and no relationships were found between DTPA clearance rates and inflammatory markers (lymphocytes, albumin, ACE) in the bronchoalveolar lavage fluid.     

Anterior tibial translation during eccentric, isokinetic quadriceps work in healthy subjects

The effect of increasing isokinetic, eccentric quadriceps torques on sagittal translation of the tibia was examined in six healthy volunteers and compared to the translation at 20 degrees of knee flexion during a drawer test with 90 N force. The tibial translation increased in a linear fashion with a mean of 0.5 mm per 20% torque increase. In 20 degrees of knee flexion, 10% of eccentric quadriceps peak torque consumed 80% of the anterior tibial translation induced by the 90 N Lachman test while eccentric quadriceps peak torque utilized 100% of the translation at the same test. The in vivo relation between muscle force and tibial translation is of importance in the treatment of patients with injury to the cruciate ligaments. The results indicate that an already low eccentric quadriceps torque causes a tibial translation that reaches the limit of the passive knee joint displacement where strain is assumed to develop in the anterior cruciate ligament. Already low eccentric quadriceps torque levels may therefore be harmful during rehabilitation after anterior cruciate ligament surgery.     

Comparing the kinematic output of the Oxford and Rizzoli Foot Models during normal gait and voluntary pathological gait in healthy adults

BackgroundThe Oxford Foot Model (OFM) and Rizzoli Foot Model (RFM) are the two most frequently used multi-segment models to measure foot kinematics. However, a comprehensive comparison of the kinematic output of these models is lacking.Research questionWhat are the differences in kinematic output between OFM and RFM during normal gait and typical pathological gait patterns in healthy adults?.MethodsA combined OFM and RFM marker set was placed on the right foot of ten healthy subjects. A static standing trial and six level walking trials were collected for normal gait and for four voluntarily adopted gait types: equinus, crouch, toe-in and toe-out. Joint angles were calculated for every trial for the hindfoot relative to shank (HF-SH), forefoot relative to hindfoot (FF-HF) and hallux relative to forefoot (HX-FF). Average static joint angles of both models were compared between models. After subtracting these offsets, the remaining dynamic angles were compared using statistical parametric mapping repeated measures ANOVAs and t-tests. Furthermore, range of motion was compared between models for every angle.ResultsFor the static posture, RFM compared to OFM measured more plantar flexion (Δ = 6°) and internal rotation (Δ = 7°) for HF-SH, more plantar flexion (Δ = 34°) and inversion (Δ = 13°) for FF-HF and more dorsal flexion (Δ = 37°) and abduction (Δ = 12°) for HX-FF. During normal walking, kinematic differences were found in various parts of the gait cycle. Moreover, range of motion was larger in the HF-SH for OFM and in FF-HF and HX-FF for RFM. The differences between models were not the same for all gait types. Equinus and toe-out gait demonstrated most pronounced differences.SignificanceDifferences are present in kinematic output between OFM and RFM, which also depend on gait type. Therefore, kinematic output of foot and ankle studies should be interpreted with careful consideration of the multi-segment foot model used.     

Directional effects of biofeedback on trunk sway during gait tasks in healthy young subjects

Biofeedback of trunk sway is a possible remedy for patients with balance disorders. Because these patients have a tendency to fall more in one direction, we investigated whether biofeedback has a directional effect on trunk sway during gait.Forty healthy young participants (mean age 23.1 years) performed 10 gait tasks with and without biofeedback. Combined vibrotactile, auditory and visual feedback on trunk sway in either the lateral or anterior–posterior (AP) direction was provided by a head-mounted actuator system. Trunk roll and pitch angles, calculated from trunk angular velocities measured with gyroscopes, were used to drive the feedback.A reduction in sway velocities occurred across all tasks regardless of feedback direction. Reductions in sway angles depended on the task. Generally, reductions were greater in pitch. For walking up and down stairs, or over barriers, pitch angle reductions were greater with AP than lateral feedback. For tandem and normal walking, reductions were similar in pitch and roll angles for both feedback directions. For walking while rotating or pitching the head or with eyes closed, only pitch angle was reduced for both feedback directions.These results indicate that the central nervous system is able to incorporate biofeedback of trunk sway from either the AP or lateral direction to achieve a reduction in both pitch and roll sway. Greater reductions in pitch suggest a greater ability to use this direction of trunk sway biofeedback during gait.     

Sit-to-walk and sit-to-stand-and-walk task dynamics are maintained during rising at an elevated seat-height independent of lead-limb in healthy individuals

IntroductionSit-to-walk (STW) is a common transitional motor task not usually included in rehabilitation. Typically, sit-to-stand (STS), pause, then gait initiation (GI) before walking is used, which we term sit-to-stand-and-walk (STSW). Separation between centre-of-pressure (COP) and whole-body centre-of-mass (BCOM) during GI is associated with dynamic postural stability. Rising from seats higher than knee-height (KH) is more achievable for patients, but whether this and/or lead-limb significantly affects task dynamics is unclear. This study tested whether rising from seat-heights and lead-limb affects STW and STSW task dynamics in young healthy individuals.MethodsTen (5F) young (29 ± 7.7 years) participants performed STW and STSW from a standardised position. Five trials of each task were completed at 100 and 120%KH leading with dominant and non-dominant legs. Four force-plates and optical motion capture delineated key movement events and phases with effect of seat-height and lead-limb determined by 2-way ANOVA within tasks.ResultsAt 120%KH, lower peak vertical ground-reaction-forces (vGRFs) and vertical BCOM velocities were observed during rising irrespective of lead-limb. No other parameters differed between seat-heights or lead-limbs. During GI in STSW there was more lateral, and less posterior, COP excursion than expected.ConclusionReduction in vGRFs and velocity during rising at 120%KH is consistent with reduced effort in young healthy individuals and is likely therefore to be an appropriate seat-height for patients. Lead-limb had no effect upon STSW or STW parameters suggesting that normative data independent of lead-limb can be utilised to monitor motor rehabilitation should differences be observed in patients. STSW should be considered an independent movement transition.     

Evaluating automated dynamic contrast enhanced wrist 3 T MRI in healthy volunteers: One-year longitudinal observational study

Rational and Objective

Dynamic contrast enhanced (DCE)-MRI has great potential to provide quantitative measure of inflammatory activity in rheumatoid arthritis. There is no current benchmark to establish the stability of signal in the joints of healthy subjects when imaged with DCE-MRI longitudinally, which is crucial so as to differentiate changes induced by treatment from the inherent variability of perfusion measures. The objective of this study was to test a pixel-by-pixel parametric map based approach for analysis of DCE-MRI (Dynamika) and to investigate the variability in signal characteristics over time in healthy controls using longitudinally acquired images.

Materials and Methods

10 healthy volunteers enrolled, dominant wrists were imaged with contrast enhanced 3T MRI at baseline, week 12, 24 and 52 and scored with RAMRIS, DCE-MRI was analysed using a novel quantification parametric map based approach. Radiographs were obtained at baseline and week 52 and scored using modified Sharp van der Heidje method. RAMRIS scores and dynamic MRI measures were correlated.

Results

No erosions were seen on radiographs, whereas MRI showed erosion-like changes, low grade bone marrow oedema and low-moderate synovial enhancement. The DCE-MRI parameters were stable (baseline scores, variability) (mean ± st.dev); in whole wrist analysis, ME_mean (1.3 ± 0.07, −0.08 ± 0.1 at week 24) and IRE_mean (0.008 ± 0.004, −0.002 ± 0.005 at week 12 and 24). In the rough wrist ROI, ME_mean (1.2 ± 0.07, 0.04 ± 0.02 at week 52) and IRE_mean (0.001 ± 0.0008, 0.0006 ± 0.0009 at week 52) and precise wrist ROI, ME_mean (1.2 ± 0.09, 0.04 ± 0.04 at week 52) and IRE_mean (0.001 ± 0.0008, 0.0008 ± 0.001 at week 24 and 52). The Dynamic parameters obtained using fully automated analysis demonstrated strong, statistically significant correlations with RAMRIS synovitis scores.

Conclusion

The study demonstrated that contrast enhancement does occur in healthy volunteers but the inherent variability of perfusion measures obtained with quantitative DCE-MRI method is low and stable, suggesting its suitability for longitudinal studies of inflammatory arthritis. These results also provide important information regarding potential cut-off levels for imaging remission goals in patients with RA using both RAMRIS and DCE-MRI extracted parametric parameters.     

Kinematic classification of iliotibial band syndrome in runners

Several inconsistent causative biomechanical factors are considered to be crucial in the occurrence of iliotibial band syndrome (ITBS). The focus of this study was on assessing differences in the kinematic characteristics between healthy runners [control group (CO)] and runners with ITBS in order to recommend treatment strategies to deal with this injury. Three‐dimensional kinematics of barefoot running was used in the biomechanical setup. Both groups were matched with respect to gender, height and weight. After determining drop outs, the final population comprised 36 subjects (26 male and 10 female): 18 CO and 18 ITBS (13 male and five female, each). Kinematic evaluations indicate less hip adduction and frontal range of motion at the hip joint in runners with ITBS. Furthermore, maximum hip flexion velocity and maximum knee flexion velocity were lower in runners with ITBS. Lack of joint coordination, expressed as earlier hip flexion and a tendency toward earlier knee flexion, was found to be another discriminating variable in subjects with ITBS compared with CO subjects. We assume that an increase in range of motion at the hip joint, stretching of the hip abductors, as well as stretching the hamstrings, calf muscles and hip flexors will help treat ITBS.     

Effect of 3D printed foot orthoses stiffness and design on foot kinematics and plantar pressures in healthy people

BackgroundFoot orthoses (FOs) have been widely prescribed to alter various lower limb disorders. FOs’ geometrical design and material properties have been shown to influence their impact on foot biomechanics. New technologies such as 3D printing provide the potential to produce custom shapes and add functionalities to FOs by adding extra-components.Research questionThe purpose of this study was to determine the effect of 3D printed FOs stiffness and newly design postings on foot kinematics and plantar pressures in healthy people.MethodsTwo pairs of ¾ length prefabricated 3D printed FOs were administered to 15 healthy participants with normal foot posture. FOs were of different stiffness and were designed so that extra-components, innovative flat postings, could be inserted at the rearfoot. In-shoe multi-segment foot kinematics as well as plantar pressures were recorded while participants walked on a treadmill. One-way ANOVAs using statistical non-parametric mapping were performed to estimate the effect of FOs stiffness and then the addition of postings during the stance phase of walking.ResultsIncreasing FOs stiffness altered frontal and transverse plane foot kinematics, especially by further reducing rearfoot eversion and increasing the rearfoot abduction. Postings had notable effect on rearfoot frontal plane kinematics, by enhancing FOs effect. Looking at plantar pressures, wearing FOs was associated with a shift of the loads from the rearfoot to the midfoot region. Higher peak pressures under the rearfoot and midfoot (up to +31.7 %) were also observed when increasing the stiffness of the FOs.Significance3D printing techniques offer a wide range of possibilities in terms of material properties and design, providing clinicians the opportunity to administer FOs that could be modulated according to pathologies as well as during the treatment by adding extra-components. Further studies including people presenting musculoskeletal disorders are required.     

Differences in muscle synergies between healthy subjects and transfemoral amputees during normal transient-state walking speed

BackgroundLower limb amputation is a major public health issue globally, and its prevalence is increasing significantly around the world. Previous studies on lower limb amputees showed analogous complexity implemented by the neurological system which does not depend on the level of amputation.Research questionWhat are the differences in muscle synergies between healthy subjects (HS) and transfemoral amputees (TFA) during self-selected normal transient-state walking speed?Methodsthirteen male HS and eleven male TFA participated in this study. Surface electromyography (sEMG) data were collected from HS dominant leg and TFA intact limb. Concatenated non-negative matrix factorization (CNMF) was used to extract muscle synergy components synergy vectors (S) and activation coefficient profiles (C). Correlation between a pair of synergy vectors from HS and TFA was analyzed by means of the coefficient of determination (R²). Statistical parametric mapping (SPM) was used to compare the temporal components of the muscle synergies between groups.Resultsthe highest correlation was perceived in synergy 2 (S2) and 3 (S3) and the lowest in synergy 1 (S1) and 4 (S4) between HS and TFA. Statistically significant differences were observed in all of the activation coefficients, particularly during the stance phase. Significant lag in the activation coefficient of S2 (due mainly to activated plantarflexors) resulted in a statistically larger portion of the gait cycle (GC) in stance phase in TFA.SignificanceUnderstanding the activation patterns of lower limb amputees’ muscles that control their intact leg (IL) and prosthetic leg (PL) joints could lead to greater knowledge of neuromuscular compensation strategies in amputees. Studying the low-dimensional muscle synergy patterns in the lower limbs can further this understanding. The findings in this study could contribute to improving gait rehabilitation of lower limb amputees and development of the new generation of prostheses.     

Position of the major curve influences asymmetrical trunk kinematics during gait in adolescent idiopathic scoliosis

Background and purposeAdolescent idiopathic scoliosis (AIS) is a structural, lateral curvature with rotation of the spine that develops around puberty. The influence of this spinal deformity on three-dimensional trunk movements during gait has not yet been elucidated. The aim of this study was to determine the influence of spinal curve pattern (single thoracic curve vs. single lumbar curve) on trunk kinematics during gait.MethodsTwenty-two patients with a single thoracic curve (Lenke type 1) and 17 patients with a single lumbar curve (Lenke type 5) were included in this study. Trunk symmetry in the sagittal, coronal, and transverse planes during gait was evaluated using an optoelectronic motion capture system.ResultsIn the type 1 group, the trunk was significantly rotated towards the concave side in the transverse plane during gait (mean difference of transverse rotation angle between concave side load and the convex side load, 8.8 ± 0.6°, p < 0.01). In the type 5 group, the trunk was significantly rotated towards the convex side in the coronal plane throughout the stance phase of gait (mean difference of coronal inclination angle, 1.9 ± 0.3°, p < 0.05).ConclusionsThe AIS patients with a single thoracic curve showed asymmetrical trunk movement in the transverse plane, and patients with a single lumbar curve showed asymmetrical trunk movement in the coronal plane. These results indicate that the spinal curve pattern influenced trunk kinematics, and suggest that the global postural control strategy of patients with AIS differs according to the curve pattern.     

Hip and knee joints are more stabilized than driven during the stance phase of gait: an analysis of the 3D angle between joint moment and joint angular velocity

Joint power is commonly used in orthopaedics, ergonomics or sports analysis but its clinical interpretation remains controversial. Some basic principles on muscle actions and energy transfer have been proposed in 2D. The decomposition of power on 3 axes, although questionable, allows the same analysis in 3D. However, these basic principles have been widely criticized, mainly because bi-articular muscles must be considered. This requires a more complex computation in order to determine how the individual muscle force contributes to drive the joint. Conversely, with simple 3D inverse dynamics, the analysis of both joint moment and angular velocity directions is essential to clarify when the joint moment can contribute or not to drive the joint. The present study evaluates the 3D angle between the joint moment and the joint angular velocity and investigates when the hip, knee and ankle joints are predominantly driven (angle close to 0 degrees and 180 degrees ) or stabilized (angle close to 90 degrees ) during gait. The 3D angle curves show that the three joints are never fully but only partially driven and that the hip and knee joints are mainly stabilized during the stance phase. The notion of stabilization should be further investigated, especially for subjects with motion disorders or prostheses.     

Upper extremity kinematics during functional activities: three-dimensional studies in a normal pediatric population

Children with brachial plexus birth palsy, burns, cerebral palsy, spinal cord injury and upper limb malformations may have diminished ability to perform activities of daily living (ADLs) due to limited upper extremity (UE) motion. Three-dimensional (3D) imaging techniques provide a way to document multi-planar functional limitations in the UE. These techniques have not been routinely used for this purpose primarily due to a lack of standardized protocols stemming from the complex nature of UE motion. Before 3D techniques can be routinely used for quantitative analysis and determination of functional limitations, standard activities and nomenclature for UE motion must be determined, and normal arm motion defined. This study establishes a normative pediatric database of 3D kinematic values during selected ADLs, enabling future comparisons with pathologic movements. Regardless of their underlying condition, children with limited UE function and ADL performance can be studied using this protocol and compared with this age-matched normal population.     

Relation between peak knee flexion angle and knee ankle kinetics in single-leg jump landing from running: a pilot study on male handball players to prevent ACL injury

Objectives: The relationship between knee kinematics and knee-ankle kinetics during the landing phase of single leg jumping has been widely studied to identify proper strategies for preventing non-contact ACL injury. However, there is a lack of study on knee-ankle kinetics at peak knee flexion angle during jumping from running. Hence, the purpose of this study is to establish the relationship between peak knee flexion angle, knee extension moment, ankle plantar flexion moment and ground reaction force in handball players in order to protect ACL from excessive stress during single leg jumping. In addition, the study also clarifies the role of calf muscles in relieving part of ACL stresses with different knee flexion angles during landing.

Methods: Fifteen active male elite handball players of Saudi Arabia have participated in this study (Age = 22.6 ± 3.5years, Height = 182 ± 3.7 cm, Weight = 87.5 ± 10.2 kg). The players performed three successful landings of single-leg jump following running a fixed distance of about 450cm. The data were collected using a 3D motion capture and analysis system (VICON).

Results: Pearson product moment correlation coefficients showed that greater peak knee flexion angle is related significantly to both lesser knee extension moment (r = -.623, P = .013) and vertical component of ground reaction force (VGRF) (r = -.688, P = .005) in landing phase. Moreover, increasing the peak knee flexion angle in landing phase tends to increase the ankle plantar flexion moment significantly (r = .832, P = .000).

Conclusion: With an increase of the peak knee flexion angle during single leg jump landing from running, there would be less knee extension moment, low impact force and more plantar flexion moment. As such, the clinical implication of this study is that there may be a possible protective mechanism by increasing the knee flexion angle during landing phase, which tends to protect the ACL from vigorous strain and injuries.