Contact Foot Research Articles

Relationship between glenohumeral horizontal abduction angle and scapular internal rotation angle at maximum shoulder external rotation during baseball pitching

BackgroundIncreased scapulothoracic (ST) internal rotation at maximum external rotation (MER) during baseball pitching can decrease glenohumeral (GH) horizontal adduction, leading to excessive GH horizontal abduction. However, few studies have examined this direct relationship, and none have investigated the ST internal rotation angle at stride foot contact (FC) and MER. This study investigated the relationships between GH horizontal adduction and ST internal rotation angles at MER and between ST internal rotation angles at FC and MER. MethodsWe recruited 15 asymptomatic collegiate baseball pitchers and assessed the ST internal rotation angle at FC and MER and GH horizontal adduction angle at MER during pitching using an optical motion tracking system. Pearson’s correlation coefficients determined the relationships between GH horizontal adduction and ST internal rotation angles at MER and between ST internal rotation angles at FC and MER. ResultsThe GH horizontal adduction angle at MER was significantly related to the ST internal rotation angle at MER (r = -0.58, p = 0.022). The ST internal rotation angle at FC was significantly related to the ST internal rotation angle at MER (r = 0.53, p = 0.045). ConclusionsThe GH horizontal adduction angle at MER is associated with the ST internal rotation angle at MER in asymptomatic collegiate baseball pitchers and the ST internal rotation angle at FC is related to the ST internal rotation angle at MER. Thus, the scapula and humerus should be controlled from FC to MER during pitching to reduce internal impingement risk in asymptomatic baseball pitchers.

Forearm Pronation at Foot Contact: A Biomechanical Motion-Capture Analysis in High School and Professional Pitchers.

It has previously been speculated that baseball pitchers who display excessive forearm pronation at foot contact (FC) have a higher propensity toward ulnar collateral ligament injury and subsequent surgery. To evaluate the association between degree of forearm pronation/supination at FC and throwing arm kinetics in high school and professional pitchers, at both the individual (intrapitcher) and the group (interpitcher) level. Descriptive laboratory study. High school (n = 41) and professional (n = 196) pitchers threw 8 to 12 fastballs while being assessed with a 3-dimensional motion-capture system (480 Hz). Pitchers at each playing level were divided into a supination or pronation subgroup depending on degree of forearm pronation at FC. Regression models were built to observe the relationship between forearm pronation at FC and kinetic and kinematic parameters of interest. At both the individual and the group level of high school and professional pitchers, there was no significant correlation between forearm pronation at FC and elbow varus torque (P min = .21). For every 10° increase in forearm pronation at FC in the individual high school pitcher, elbow flexion at FC decreased by 5°, whereas maximum elbow extension velocity was achieved 0.6% later in the pitch. In addition, elbow medial force increased by 4.1 N and elbow varus torque increased by 0.8 N·m for every 10° increase in forearm supination at FC. For every 10° increase in forearm supination in the individual professional pitcher, ball velocity increased by 0.5 m/s, shoulder external rotation at FC decreased by 11°, and elbow medial force decreased by 5.5 N. Supination- or pronation-predominant forearm motion during the pitch did not significantly differ between playing levels. Excessive forearm pronation at FC was not a significant risk factor for increased throwing arm kinetics for high school or professional pitchers. There was a weak positive association between forearm supination at FC and elbow varus torque in the individual high school pitcher. Ultimately, coaches and pitchers may be better served by redirecting their focus to other mechanical aspects of the pitch that may have stronger associations with injury risk implications as well as performance.

The influence of excessive ipsilateral trunk tilt on upper-extremity throwing mechanics: a newly characterized parameter for biomechanical evaluation in high school and professional pitchers.

Although contralateral trunk tilt has been recognized, the phenomenon of excessive ipsilateral trunk tilt, often observed during earlier portions of the pitch, has not been explored as a potential correlate with throwing-arm kinetics among baseball pitchers. The purpose of this study was to evaluate kinetic and kinematic parameters among high school and professional pitchers related to excessive ipsilateral and contralateral trunk tilt. Professional and high school pitchers were assessed with a 3-dimensional motion capture system (480 Hz) while pitching. Pitchers were grouped as follows: excessive ipsilateral tilt at foot contact (FC), neutral, or excessive contralateral tilt at ball release (BR). Trunk and shoulder kinematics as well as throwing-arm kinetics were compared between subgroups via post hoc regression analysis. Professional pitchers (n=287) had significantly higher ipsilateral trunk tilt at FC (P<.001) than high school pitchers (n=59). High school pitchers with excessive contralateral trunk tilt at BR experienced significantly higher shoulder superior force (27.0%±7.4% body weight [BW] vs. 17.6%±5.1% BW, P<.001) and shoulder anterior force (39.6%±8.2% BW vs. 35.7%±5.4% BW, P<.001) compared with the ipsilateral trunk tilt cohort but had comparable ball velocity (30.2±3.2 m/s vs. 30.4±2.1 m/s, P=.633). For professionals, for every 10° increase in ipsilateral trunk tilt at FC, ball velocity increased by 0.2 m/s (B = 0.02, β = 0.07, standard error [SE] = 0.005, P= .010) whereas elbow varus torque decreased by 0.1% BW × height (B = -0.01, β = -0.08, SE = 0.002, P<.001) and shoulder internal rotation torque decreased by 0.1% BW × height (B = -0.01, β = -0.07, SE = 0.002, P= .005). High school and professional pitchers with excessive ipsilateral trunk tilt at FC consistently demonstrated significantly decreased throwing-arm kinetics (shoulder anterior force and shoulder superior force for high school pitchers and shoulder internal rotation torque and elbow varus torque for professional pitchers) compared with pitchers with excessive contralateral trunk tilt at BR, with equivalent ball velocity. In addition, professional pitchers appeared to engage in significantly greater ipsilateral trunk tilt during early portions of the pitch when compared with high school pitchers, which may represent a kinetically favorable method adopted by pitchers at higher playing levels to maintain adequate ball velocity while concomitantly minimizing throwing-arm kinetics.

Paper 10: Influence of Arm Path on Elbow Varus Torque in Professional Baseball Pitchers

Objectives:Arm path, or the distance the hand travels from the glove to ball release, has become an increasingly discussed topic within the baseball community. Arm path is a combination of elbow flexion, shoulder external rotation, shoulder abduction, forearm pronation, and wrist flexion movements. Traditionally, pitchers have been taught to throw with a longer arm path during the first part of the pitching motion, which includes extending the throwing arm away from the body and delaying shoulder external rotation. Advocates of the shorter arm path have recently made a push to get pitchers to shorten up as it is thought that it results in a more efficient motion and this in turn may decrease injury risk. By shortening the arm path, the throwing arm is closer to the body in a more loaded position theoretically creating less torque on the elbow. However, there is a lack of published data to support either claim of the benefits of a shorter or longer arm path. The purpose of this study was to determine if there was a relationship between arm path and elbow varus torque in professional pitchers.Methods:Data from 285 professional pitchers were included in this study (189.9±5.9 cm, 95.1±9.8 kg). Pitchers were tested pitching 8-12 fastballs at 480 Hz using a 3D motion capture system (Motion Analysis Corp., Santa Rosa, CA). The fastest pitch from each pitcher was used in the analysis. Arm path was measured as the total path the hand marker traveled during the entire pitch. Arm path was also normalized as a percentage of arm length (%AL). The pitch was broken down into four time points: maximum knee height (MKH), foot contact (FC), maximum external rotation (MER), ball release (BR). Linear regressions were calculated to evaluate the relationship between arm path and elbow varus torque at each time point. Significance was set at p<0.05.Results:There was no significant relationship between arm path and elbow varus torque (Figure 1). Arm path did not have a significant effect on elbow varus torque for MKH to BR (r2=.04, p<0.001), MKH to FC (r2=.05, p<0.001), and FC to BR (r2=0.00, p=0.207). Furthermore, there was no significant effect on elbow varus torque for MKH to BR, MKH to FC, and FC to BR when arm path was normalized by the pitcher’s arm length (r2=0.00 p=0.262; r2=0.02 p=0.018; r2=0.01 p=0.081 respectively).Conclusions:Recent anecdotal trends towards a shorter arm path in pitchers does not alter elbow varus torque as compared to both average and longer arm paths in a sample of professional pitchers. None of the studied time periods within the pitching motion revealed correlations between elbow varus torque and shorter arm paths. This suggests that total distance travelled by the arm during the pitching motion may not be a significant risk factor for injury in professional level pitchers. However, it is possible that components of arm path (i.e. elbow flexion, shoulder rotation, and shoulder horizontal abduction) play a larger role in the influence on elbow varus torque than simply arm path. Future studies should investigate the combined effects of arm path and arm path’s components on elbow varus torque.Figure 1.Correlations of arm path to elbow varus torque during a pitch. The left hand column measures arm path in centimeters and the right hand column uses arm path normalized to pitcher’s arm length. There were no correlations in arm path to elbow varus torque. Maximum knee height. MKII; FC. foot contact; BR. ball release.

Paper 35: High School and Professional Pitchers with Early Excessive Ipsilateral Trunk Tilt: A Newly Characterized Parameter for Biomechanical Evaluation

Objectives:Though contralateral trunk tilt has been frequently studied in baseball pitchers, the phenomena of excessive ipsilateral trunk tilt has not been explored as a potential correlate with throwing arm kinetics. Excessive ipsilateral trunk tilt is often observed during earlier portions of the pitch cycle. High school pitchers with excessive contralateral trunk tilt during the late cocking phase of pitching have been noted to have significantly faster ball velocity, as well as increased elbow distraction force, shoulder distraction force, elbow varus torque, and shoulder internal rotation torque. Collegiate pitchers with excessive contralateral trunk tilt at maximum shoulder external rotation and at ball release have significantly faster ball velocity and higher elbow varus torque. The purpose of this study was to evaluate the effect of ipsilateral and contralateral trunk tilt on kinetic and kinematic parameters among high school and professional baseball pitchers.Methods:Professional and high school baseball pitchers were assessed with 3D-motion capture technology (480 Hz) while pitching in a controlled laboratory setting. Pitchers were grouped into ipsilateral, neutral, or contralateral trunk tilt groups based on the degree of lateral trunk tilt at foot contact (FC) and ball release (BR) (Figure 1). Trunk and shoulder kinematics, as well as throwing arm kinetics, were compared between subgroups with post-hoc regression analysis.Results:Professional pitchers (n=287) had significantly higher ipsilateral trunk tilt at FC (p<0.001) compared to high school pitchers (n=59) (Figure 2). High school pitchers with excessive contralateral trunk tilt at BR experienced significantly higher shoulder superior force (27.0 ± 7.4 vs. 17.6 ± 5.1 %Body Weight [BW] respectively, p<0.001) and shoulder anterior force (39.6 ± 8.2 vs. 35.7 ± 5.4 %BW respectively, p<0.001) compared to the ipsilateral trunk tilt cohort, while accomplishing comparable ball velocity (30.2±3.2 vs. 30.4±2.1m/s, p=0.633). For professional pitchers, for every 10° increase in ipsilateral trunk tilt at FC, ball velocity increased by 0.2 m/s (B: 0.02, β: 0.07, SE: 0.005, p=0.010), while elbow varus torque (EVT) decreased by 0.1%BWxHeight (B: -0.01, β: -0.08, SE: 0.002, p<0.001) and shoulder internal rotation torque (SIRT) decreased by 0.1 %BWxHeight (B: -0.01, β: -0.07, SE: 0.002, p=0.005).Conclusions:High school and professional pitchers with excessive ipsilateral trunk tilt at FC consistently demonstrated significantly decreased throwing arm kinetics (high school: shoulder anterior force, shoulder superior force; professional: SIRT, EVT) compared to pitchers with excessive contralateral trunk tilt at BR, with at least equivalent ball velocity. In addition, professional pitchers already appear to engage in significantly greater ipsilateral trunk tilt at early portions of the pitch cycle when compared to high school pitchers, which may represent a kinetically favorable method adopted by pitchers at higher playing levels to maintain adequate ball velocity while concomitantly minimizing throwing arm kinetics. While contralateral trunk tilt has previously been associated with throwing arm kinetics in high school and collegiate pitchers, ipsilateral lateral trunk tilt has not been assessed in professional pitchers, a subgroup characterized by distinct pitching kinematics compared to amateur pitchers. Further research is warranted to determine if the kinetic impact of trunk tilt during the throwing motion of baseball pitchers impacts the risk of injury.UPLOAD-https://planion-client-files.s3.amazonaws.com/AOSSM/blobs/ada6d538-50e8-460e-ac42-c385825f1ce4/1/Trunk_Tilt_Fig_2.docx Figure 1.Lateral trunk till in pitchers; (+) indicates ipsilaleral trunk till, (-) indicates contralateral trunk tilt.

Relationships between throwing mechanics and shoulder anterior force in high school and professional baseball pitchers.

Excessive shoulder anterior force has been implicated in pathology of the rotator cuff in little league and professional baseball pitchers; in particular, anterior laxity, posterior stiffness, and glenohumeral joint impingement. Distinctly characterized motions associated with excessive shoulder anterior force remain poorly understood. High school and professional pitchers were instructed to throw fastballs while being evaluated with 3D motion capture (480 Hz). A supplementary random forest model was designed and implemented to identify the most important features for regressing to shoulder anterior force, with subsequent standardized regression coefficients to quantify directionality. 130 high school pitchers (16.3 ± 1.2 yrs; 179.9 ± 7.7 cm; 74.5 ± 12.0 kg) and 322 professionals (21.9 ± 2.1 yrs; 189.7 ± 5.7 cm; 94.8 ± 9.5 kg) were included. Random forest models determined nearly all the variance for professional pitchers (R2 = 0.96), and less than half for high school pitchers (R2 = 0.41). Important predictors of shoulder anterior force in high school pitchers included: trunk flexion at maximum shoulder external rotation (MER) (X.IncMSE = 2.4, β = -0.23, p < 0.001), shoulder external rotation at ball release (BR)(X.IncMSE = 1.7, β = -0.34, p < 0.001), and shoulder abduction at BR (X.IncMSE = 3.1, β = 0.17, p < 0.001). In professional pitchers, shoulder horizontal adduction at foot contact (FC) was the highest predictor (X.IncMSE = 13.9, β = 0.50, p < 0.001), followed by shoulder external rotation at FC (X.IncMSE = 3.6, β = 0.26, p < 0.001), and maximum elbow extension velocity (X.IncMSE = 8.5, β = 0.19, p < 0.001). A random forest model successfully selected a subset of features that accounted for the majority of variance in shoulder anterior force for professional pitchers; however, less than half of the variance was accounted for in high school pitchers. Temporal and kinematic movements at the shoulder were prominent predictors of shoulder anterior force for both groups. : Our statistical model successfully identified a combination of features with the ability to adequately explain the majority of variance in anterior shoulder force among high school and professional pitchers. To minimize shoulder anterior force, high school pitchers should emphasize decreased shoulder abduction at BR, while professionals can decrease shoulder horizontal adduction at FC.

Locomotion Mode Transition Prediction Based on Gait-Event Identification Using Wearable Sensors and Multilayer Perceptrons.

People walk on different types of terrain daily; for instance, level-ground walking, ramp and stair ascent and descent, and stepping over obstacles are common activities in daily life. Movement patterns change as people move from one terrain to another. The prediction of transitions between locomotion modes is important for developing assistive devices, such as exoskeletons, as the optimal assistive strategies may differ for different locomotion modes. The prediction of locomotion mode transitions is often accompanied by gait-event detection that provides important information during locomotion about critical events, such as foot contact (FC) and toe off (TO). In this study, we introduce a method to integrate locomotion mode prediction and gait-event identification into one machine learning framework, comprised of two multilayer perceptrons (MLP). Input features to the framework were from fused data from wearable sensors—specifically, electromyography sensors and inertial measurement units. The first MLP successfully identified FC and TO, FC events were identified accurately, and a small number of misclassifications only occurred near TO events. A small time difference (2.5 ms and −5.3 ms for FC and TO, respectively) was found between predicted and true gait events. The second MLP correctly identified walking, ramp ascent, and ramp descent transitions with the best aggregate accuracy of 96.3%, 90.1%, and 90.6%, respectively, with sufficient prediction time prior to the critical events. The models in this study demonstrate high accuracy in predicting transitions between different locomotion modes in the same side’s mid- to late stance of the stride prior to the step into the new mode using data from EMG and IMU sensors. Our results may help assistive devices achieve smooth and seamless transitions in different locomotion modes for those with motor disorders.

Gait Phase Estimation by Using LSTM in IMU-Based Gait Analysis-Proof of Concept.

Gait phase detection in IMU-based gait analysis has some limitations due to walking style variations and physical impairments of individuals. Therefore, available algorithms may not work properly when the gait data is noisy, or the person rarely reaches a steady state of walking. The aim of this work was to employ Artificial Intelligence (AI), specifically a long short-term memory (LSTM) algorithm, to overcome these weaknesses. Three supervised LSTM-based models were designed to estimate the expected gait phases, including foot-off (FO), mid-swing (MidS) and foot-contact (FC). For collecting gait data two tri-axial inertial sensors were located above each ankle. The angular velocity magnitude, rotation matrix magnitude and free acceleration magnitude were captured for data labeling and turning detection and to strengthen the model, respectively. To do so, a train dataset based on a novel movement protocol was acquired. A validation dataset similar to a train dataset was generated as well. Five test datasets from already existing data were also created to independently evaluate the models. After testing the models on validation and test datasets, all three models demonstrated promising performance in estimating desired gait phases. The proposed approach proves the possibility of employing AI-based algorithms to predict labeled gait phases from a time series of gait data.

The Kick Motion Analysis Of Adolescent Male Soccer Player With Osgood-schlatter Disease

Osgood-Schlatter disease(OSD) is an epiphyseal disease of tibial tubercle by repeated traction of patellar tendon, especially on epiphyseal or apophyseal stage. OSD is associated with sports that involve kicking, and running, but none have analyzed the kick motion of adolescent soccer players who experienced the OSD. PURPOSE: The purpose of this study was to compare the kick motion in adolescent soccer players with and without OSD using three-dimensional motion analysis system. METHODS: We recruited 112 adolescent soccer players (13 ± 1 years old) All players went through the medical examination including the ultrasonography of tibial tubercle, and the muscle tightness test of lower limbs. We included only whose tibial tubercle stage was epiphyseal or apophyseal stage for this study and made two groups: presence of OSD on kicking leg (OSD group; n = 10) and absence of OSD or any other injuries (NP group; n = 30). We measured real-time kick motion using a three-dimensional motion analysis system (Qualisys track manager, Qualisys AB., Sweden). We placed 65 spherical markers on each anatomical landmark and calculated the angle of the lumbar spine, pelvis, hips, knees and ankles.We collected data for the following six events of kicking leg: foot contact (FC), toe off (TO), max hip extension (HE), max knee flexion (KF), ball impact (BI), and max hip flexion (HF). We used unpaired t-test to compare all the factors we measured between OSD group and NP group. RESULTS: The anthropometric index, muscle tightness, ball speed of OSD group were not different from NP group. In HE, the supporting leg’s ankle flexion angle in OSD group was smaller in OSD group(14.9±3.7 vs. 18.9±5.0 °, p=0.024). In KF, the hip abduction angle of the kicking leg was smaller(24.5±5.9 vs. 28.6±5.1 °, p=0.041)in OSD group. In HF, the lateral bending angle of pelvis toward the supporting side was significantly smaller in OSD group (-2.6±16.4 vs. 7.4±11.3 °, p=0.037) In HF, supporting leg's ankle was more dorsal flexion(0.4±14.9 vs. -14.1±14.5 °, p=0.010), more valgus(26.3±12.4 vs. 11.5±11.1 °, p=0.001)compared to NP group. CONCLUSION: OSD group had smaller dorsal flexion angle of supporting leg before and after BI. They also had smaller hip abduction angle of kicking leg before BI, and lateral bending angle of pelvis toward the supporting leg side was smaller after BI.

Effects of Increased Gluteus Muscle Activation on Hip and Trunk Kinematics during Single-leg Landing

The gluteus maximus (GM) has a triplanar function at the hip joint. It was hypothesized that increased GM activation before and after foot contact (FC) on landing would affect triplanar hip and trunk kinematics and anterior cruciate ligament (ACL) injury risk. PURPOSE: To examine how increased GM activation before and after FC affect hip angles and trunk inclination during single-leg landing. METHODS: A double-leg drop jump from a 30-cm box, followed by single-leg landing onto a force plate, was performed by 13 males and 15 females in both control (CC) and experimental conditions (EC). In EC, transcutaneous electrical stimulation was applied to increase GM activation immediately before FC and during single-leg landing. Kinetic and kinematic data were collected using a force plate and 3-dimensional electromagnetic motion tracking system, respectively. Hip joint angles and sacrum and thorax inclination angles in space on FC, peak ground reaction force (GRFpk), and peak knee extensor moment (KEMpk) during single-leg landing were calculated. Comparisons were performed using two-way (sex×conditions) repeated measures analysis of variance with a significance level < .05. RESULTS: The hip joint exhibited more abduction (EC vs. CC at FC, GRFpk, and KEMpk, respectively: -13.2 ± 7.8° vs. -9.5 ± 6.3°, -8.9 ± 7.7° vs. -4.9 ± 6.8°, -3.3 ± 8.9° vs. -.2 ± 6.5°) and external rotation (-14.8 ± 8.5° vs. -9.8 ± 9.9°, -8.0 ± 3.6° vs. -3.6 ± 9.7°, -6.1 ± 9.7° vs. -1.6 ± 11.2°) at all time points in EC than in CC. The sacrum showed more lateral inclination toward the supporting leg at all time points (14.3 ± 6.4° vs. 11.1 ± 6.4°, 12.1 ± 6.4° vs. 9.0 ± 6.1°, 8.9 ± 7.1° vs. 6.7 ± 6.2°) and more erect position at KEMpk in EC (-1.0 ± 10.6°) than at CC (-4.6 ± 10.5°). No significant differences were observed in thoracic inclination angles. No significant interactions were observed among all variables. CONCLUSIONS: Increased GM before and after FC on single- leg landing may have positive effects on frontal and transverse plane hip motion to reduce ACL injury risk. However, excessive GM activation may result in excessive trunk lean toward the supporting leg and more erect position, which increase risk for ACL loading. Thus, appropriate GM activation is necessary to protect the ACL during single-leg landing.

The Role of Lumbopelvic-Hip Complex Stability in Softball Throwing Mechanics.

Studies have found that a 20% reduction in energy generation from the lumbopelvic-hip complex during overhead throws leads to a 34% increase in load on the shoulder. The purpose of this study was to assess the effects of lumbopelvic-hip complex stability, via the single leg squat assessment, on throwing mechanics of softball athletes. Prospective cohort study. Laboratory setting. A total of 50 softball athletes (164.0 [104.0]cm, 65.6 [11.3]kg, 16.3 [3.8]y, 8.61 [3.62]y of experience) performed 3 overhead throws and a single leg squat on each leg. Four stability groups were derived: (1)stable on both legs (bilateral stability), (2)unstable on the throwing side leg (TS instability) and stable on the nonthrowing side leg, (3)unstable on the nonthrowing side leg (NTS instability) and stable on the throwing side leg, and (4)unstable on both legs (bilateral instability). All throws were analyzed across 4 throwing events: foot contact (FC), maximum external shoulder rotation (MER), ball release (BR), and maximum internal shoulder rotation (MIR). Mann-Whitney U tests revealed significant differences between the bilateral stability and the TS instability groups in trunk flexion at BR; the bilateral stability and the NTS instability groups in trunk flexion at BR, shoulder horizontal abduction at FC, shoulder rotation at FC, and pelvis flexion at MIR; the TS instability and the bilateral instability groups in trunk rotation at FC; and the NTS instability and the bilateral instability groups in trunk flexion at MER and shoulder rotation at FC. These findings demonstrate the different mechanisms in which energy can be lost through lumbopelvic-hip complex instability as evident in throwing mechanics. The findings from this study suggest that the current methods used for classification could act as a tool for coaches, physicians, and athletic trainers when assessing their athletes' injury susceptibility.

Development of an embedded gait analysis system for brain damaged patients

Optical motion analysis systems are widely used to evaluate the efficiency of treatment/rehabilitation for poststroke patients. These systems are only available in clinical settings due to their size/cost and need of complicate post processing. This paper presents the development of an embedded low cost and easy-to-use system for gait analysis, which measures the joints angles and automatically detects foot-off (FO) and foot-contact (FC) events of stroke walking. The system uses 7 wireless inertial measurement unit (IMUs) to measure the body segments orientations and 2 ultra-wideband (UWB) rangefinders placed near the heels for foot relative distance measurement. Data from sensors are synchronized and recorded in SD card at 70 Hz by controller (AtoutNovation, France). The locomotion of 14 stroke and 4 healthy subjects have been evaluated simultaneously with proposed system and a 3D motion analysis system. Eight gait records at a self-selected speed along 8 m walkway were performed by each subject. The joint angles in sagittal plane were calculated using orientations of segments. To avoid perturbation of external magnetic field (e.g. treadmill walking), the magnetometer was not used, therefore the system cannot calculate 3D joints values. Relative feet distance and foot angular velocity were used to determinate gait events. The joints angles in sagittal plane are segmented, normalized and averaged in gait cycle automatically based on detected gait events. The comparisons between proposed system and motion capture system showed a precision of 28.6 ± 28.3 ms for FC detection and 18.1 ± 18.0 for FO events. 98.9% of FC and 98.8% of FO events were automatically detected. The comparisons show a precision of 4.3 ± 2.9° for knee, 2.9 ± 2.8° for ankle and 4.8 ± 3.4° for hip. Correlation coefficient of all joint angles are higher than 0.97. The proposed system constitutes a new low cost and wearable device allowing to assess stroke patient's locomotion. Indeed, gait event detection accuracy is acceptable since the data are sampled each 14 ms. The joint angles have a high correlation coefficient and the differences between the 2 systems are limited. Its performance and easy use make it a good candidate for pathological gait analysis in ecological conditions.

Use Of Inertial Magnetic Sensors To Implement Kinematic Methods To Detect Foot Contact During Running

Biomechanics of the stance phase of running is of interest in relation to injury development. Studying the stance phase requires proper detection of foot contact (FC). The onset of vertical ground reaction force (GRF) is considered the gold standard in a laboratory setting to detect FC. In the absence of GRF data, motion analysis can be used to measure peak downward velocity of the pelvis (PDVP) with a 15ms offset which showed good relation with FC during treadmill running at one speed (1). Inertial sensors can measure kinematic parameters like PDVP outside the laboratory setting. Peak tibial acceleration (PTA) is a parameter of interest in running injury development which can be measured with inertial sensors and may also be used to detect FC outside the laboratory. PURPOSE: To assess the effectiveness of these kinematic methods using inertial measurement units (IMUs) to detect FC during running at different speeds. METHODS: 3 male runners (28 ± 8.5 yrs) ran on an instrumented treadmill at 6 speeds (10-15 km/h) for 1 minute each, wearing a suit equipped with IMUs at the tibia and sacrum. FC was determined based on GRF data of the treadmill (1000 Hz; threshold of 20N) and IMU data (240Hz). PDVP was obtained from a single integration of pelvic acceleration in the global frame. PTA was determined from the acceleration data measured in the local tibia frame. The 95% limits of agreement were used to compare each method to the gold standard (i.e., GRF). RESULTS:Table 1: The offset and 95% limits of agreement for the two kinematic methods with respect to the gold standard for 6 running speeds.CONCLUSION: This study showed that a novel IMU-based method of detecting FC using PTA and PDVP showed good similarity with FC detection based on GRF at all running speeds. The different time offsets among running speeds should be considered when implementing these kinematic methods to detect FC. This opens up new possibilities for studying running mechanics outside the laboratory. REFERENCES: 1. Milner CE, Paquette MR. A kinematic method to detect foot contact during running for all foot strike patterns. J Biomech. 2015. 18; 48(12): 3502–5

Kinematics of Softball Hitting Off of a Tee versus Front Toss

Hitting a baseball or softball is one of the most difficult skills in sport. Use of a batting tee as a training technique is viewed as principle for establishing and improving basic fundamentals of hitting. PURPOSE: To determine lower extremity (knee flexion, pelvis rotation) and trunk (flexion, lateral flexion and rotation) kinematics hitting off a tee and hitting front toss. It was hypothesized that there would be no difference in lower extremity and trunk kinematics between the two conditions. METHODS: Nineteen National Collegiate Athletic Association (NCAA) Division I collegiate softball players (20.51±1.53 yrs; 68.99±7.68 kg; 166.87±6.00 cm) participated. Participants were instructed to execute five maximal effort swings hitting from a tee and five maximal effort swings hitting front toss from a pitcher at 9.14 m (30 ft). The hitting motion was divided into five events: stance (ST), load (LD), foot contact (FC), ball contact (BC), and follow-through (FT). RESULTS: Data failed the test of normality; therefore, a Wilcoxon signed-rank test was used to determine if there were median differences in hitting kinematics between two hitting conditions during each hitting event. Results revealed kinematic differences in trunk flexion at load (z = -2.55, p = 0.01). No other significant results were found between hitting events and examined variables during each condition. CONCLUSION: Though there were minimal kinematic differences in the two hitting conditions, these differences were at swing initiation and not exhibited beyond ball contact. These findings are beneficial for this population as decreased variability in swing mechanics across various conditions is desired. Therefore, it is suggested that future research continue to examine hitting mechanics from not only a kinematic approach but also from a kinetic and performance approach.

Rigid Ankle Foot Orthosis Deteriorates Mediolateral Balance Control and Vertical Braking during Gait Initiation.

Rigid ankle-foot orthoses (AFO) are commonly used for impeding foot drop during the swing phase of gait. They also reduce pain and improve gait kinematics in patients with weakness or loss of integrity of ankle-foot complex structures due to various pathological conditions. However, this comes at the price of constraining ankle joint mobility, which might affect propulsive force generation and balance control. The present study examined the effects of wearing an AFO on biomechanical variables and electromyographic activity of tibialis anterior (TA) and soleus muscles during gait initiation (GI). Nineteen healthy adults participated in the study. They initiated gait at a self-paced speed with no ankle constraint as well as wearing an AFO on the stance leg, or bilaterally. Constraining the stance leg ankle decreased TA activity ipsilaterally during the anticipatory postural adjustment (APA) of GI, and ipsilateral soleus activity during step execution. In the sagittal plane, the decrease in the stance leg TA activity reduced the backward displacement of the center of pressure (CoP) resulting in a reduction of the forward velocity of the center of mass (CoM) measured at foot contact (FC). In the frontal plane, wearing the AFO reduced the displacement of the CoP in the direction of the swing leg during the APA phase. The mediolateral velocity of the CoM increased during single-stance prompting a larger step width to recover balance. During step execution, the CoM vertical downward velocity is normally reduced in order to lessen the impact of the swing leg with the floor and facilitates the rise of the CoM that occurs during the subsequent double-support phase. The reduction in stance leg soleus activity caused by constraining the ankle weakened the vertical braking of the CoM during step execution. This caused the absolute instantaneous vertical velocity of the CoM at FC to be greater in the constrained conditions with respect to the control condition. From a rehabilitation perspective, passively- or actively-powered assistive AFOs could correct for the reduction in muscle activity and enhance balance control during GI of patients.

The Neuro-Mechanical Processes That Underlie Goal-Directed Medio-Lateral APA during Gait Initiation.

Gait initiation (GI) involves passing from bipedal to unipedal stance. It requires a rapid movement of the center of foot pressure (CoP) towards the future swing foot and of the center of mass (CoM) in the direction of the stance foot prior to the incoming step. This anticipatory postural adjustment (APA) allows disengaging the swing leg from the ground and establishing favorable conditions for stepping. This study aimed to describe the neuro-mechanical process that underlies the goal-directed medio-lateral (ML) APA. We hypothesized that controlled knee flexion of the stance leg contributes to the initial ML displacement of the CoP and to the calibration of the first step. Fourteen subjects initiated gait starting from three different initial stance widths of 15 cm (Small), 30 cm (Medium), and 45 cm (Large). Optoelectronic, force platform and electromyogram (EMG) measurements were performed. During APA, soleus activity diminished bilaterally, while tibialis anterior (TA) activity increased, more so in the stance leg than in the swing leg, and to a larger extent with increasing initial stance width. Knee flexion of the stance leg was observed during APA and correlated with the ML CoP displacement towards the swing leg. ML CoP and CoM displacements during APA increased with increasing stance width. The activity of stance-leg TA was correlated with the degree of knee flexion. Swing-leg tensor fasciae latae (TFL) was also active during APA. Across subjects, when stance-leg tibialis activity was low, TFL activity was large and vice versa. The modulation of the ML CoP position during APA allowed the gravity-driven torque to place the CoM just lateral to the stance foot during step execution. Accordingly, the gravity-driven torque, the ML CoM velocity during step execution, and the step width at foot contact (FC) were lower in the Small and greater in the Large condition. Consequently, the position of the stepping foot at FC remained close to the sagittal plane in all three conditions. Conclusively, coordinated activation of hip abductors and ankle dorsiflexors during APA displaces the CoP towards the swing leg, and sets the contact position for the swing foot.

Kinematics and Kinetics of Youth Baseball Catchers and Pitchers

The purpose of this study was to compare the throwing kinematics and kinetics of youth catchers and pitchers. It was hypothesized that catchers and pitchers would exhibit differences throughout the throwing motion. Descriptive statistics were used to investigate kinematics during the four events of throwing: foot contact (FC), maximum shoulder external rotation (MER), ball release (BR) and maximum shoulder internal rotation (MIR). Additionally, kinetics were investigated within phases of the events: Phase 1 (cocking; FC to MER), Phase 2 (acceleration; MER to BR) and Phase 3 (deceleration; BR to MIR). Results revealed significant difference in torso flexion, lateral flexion, pelvis lateral flexion and segment velocities between the catchers and pitchers. Based on data from the current study, it appears that the youth catchers execute their throw as they have been instructed. It is unclear if the throwing mechanics displayed by these youth are efficient for a catcher, thus further investigation is needed to determine long-term injury susceptibility.

Torso Kinematics during Stair Descent in Pregnancy

Pregnant women demonstrate altered torso kinematics during gait: namely, increased anterior pelvic tilt, posterior thoracic lean, and side-to-side movement. Fall-risk is elevated in pregnancy. 40% of falls in pregnancy occur during staircase locomotion. The extent to which torso mechanics are altered during staircase gait in pregnancy has not been reported. PURPOSE: To examine the effect of pregnancy on thoracopelvic kinematics and mediolateral motion of the spine during stair descent. METHODS: Data were collected on 26 pregnant women in the mid-2nd and 3rd trimesters and on 28 control women. An 8 camera motion capture system (120 Hz) collected data of subjects walking down a four step staircase at their self-selected speed. Subjects wore a modified Helen Hayes marker set. Foot contact (FC) of two sequential right foot contacts was indicated by force plate data (1080 Hz). 3D thoracic and pelvic angles were determined at FC during descent. Frontal plane movement of the C7 and L3 markers and max and min thoracic and pelvic angles and ROMs were determined. An ANOVA examined differences between pregnant women in their 2nd trimester, 3rd trimester, and controls (α=0.05). RESULTS: Pregnant women in their 3rd trimester demonstrated increased anterior pelvic tilt and posterior thoracic lean during stair descent (Table 1). Thoracic rotation at FC was increased in late pregnancy (p=0.12; Control: 3.4±5.3°, 2nd tri.: 4.0±5.3°, 3rd tri.: 6.2±4.4°). CONCLUSIONS: Increased abdominal volume in the 3rd trimester likely resulted in altered sagittal plane kinematics. Increased anterior pelvic tilt and posterior thoracic lean make it more difficult for the pregnant women to see the stairs below them. This combination may be related to the high risk of falling during staircase descent. *Funding: NIOSH K01 008458.Table 1: Sagittal plane thoracopelvic kinematics

Particular adaptations to potentially slippery surfaces: The effects of friction on consecutive postural adjustments (CPA)

This research deals with the postural adjustments that occur after the end of voluntary movement (“consecutive postural adjustments”: CPAs). The influence of a potentially slippery surface on CPA characteristics was considered, with the aim of exploring more deeply the postural component of the task-movement. Seven male adults were asked to perform a single step, as quickly as possible, to their own footprint marked on the ground. A force plate measured the resultant reaction forces along the antero-posterior axis (Rx) and the centre of pressure (COP) displacements along the antero-posterior and lateral axes (Xp and Yp). The velocity of the centre of gravity (COG) along the antero-posterior axis and the corresponding impulse (∫Rxdt) were calculated; the peak velocity (termed “progression velocity”: VxG) was measured. The required coefficient of friction (RCOF) along the progression axis (pμx) was determined. Two materials, differing by their COF, were laid at foot contact (FC), providing a rough foot contact (RoFC), and a smooth foot contact (SmFC) considered to be potentially slippery. Two step lengths were also performed: a short step (SS) and a long step (LS). Finally, the subjects completed four series of ten steps each. These were preceded by preliminary trials, to allow them to acquire the necessary adaptation to experimental conditions. The antero-posterior force time course presented a positive phase, that included APAs (“anticipatory postural adjustments”) and step execution (STEP), followed by a negative one, corresponding to CPAs. The backward impulse (CPI) was equal to the forward one (BPI), independently of friction and progression velocity. Moreover, VxG did not differ according to friction, but was faster when the step length was greater. Last CPA peak amplitudes (pCPA) were significantly greater and CPA durations (dCPA) shorter for RoFC and conversely for SmFC, contrary to APA. Finally, the results show a particular adaptation to the potentially slippery surface (SmFC). They suggest that adherence modulation at foot contact could be one of the rules for controlling COG displacement in single stepping. Consequently, the actual coefficient of friction value might be implemented in the motor programme at a higher level than the voluntary movement specific parameters.

Mechanisms of Adaptation from a Multiple to a Single Step Recovery Strategy following Repeated Exposure to Forward Loss of Balance in Older Adults

When released from an initial, static, forward lean angle and instructed to recover with a single step, some older adults are able to meet the task requirements, whereas others either stumble or fall. The purpose of the present study was to use the concept of margin of stability (MoS) to investigate balance recovery responses in the anterior-posterior direction exhibited by older single steppers, multiple steppers and those that are able to adapt from multiple to single steps following exposure to repeated forward loss of balance. One hundred and fifty-one healthy, community dwelling, older adults, aged 65–80 years, participated in the study. Participants performed four trials of the balance recovery task from each of three initial lean angles. Balance recovery responses in the anterior-posterior direction were quantified at three events; cable release (CR), toe-off (TO) and foot contact (FC), for trials performed at the intermediate lean angle. MoS was computed as the anterior-posterior distance between the forward boundary of the Base of Support (BoS) and the vertical projection of the velocity adjusted centre of mass position (XCoM). Approximately one-third of participants adapted from a multiple to a single step recovery strategy following repeated exposure to the task. MoS at FC for the single and multiple step trials in the adaptation group were intermediate between the exclusively single step group and the exclusively multiple step group, with the single step trials having a significant, 3.7 times higher MoS at FC than the multiple step trials. Consistent with differences between single and multiple steppers, adaptation from multiple to single steps was attributed to an increased BoS at FC, a reduced XCoM at FC and an increased rate of BoS displacement from TO to FC. Adaptations occurred within a single test session and suggest older adults that are close to the threshold of successful recovery can rapidly improve dynamic stability following repeated exposure to a forward loss of balance.