bluuebunny/crossref_metadata_2025 huggingface dataset:
Techniques Used in High- and Low-Scoring Hecht Vaults Performed at the 1995 World Gymnastics Championships
Authors: Takei Yoshiaki , Dunn J. Hubert , Blucker Erik P. , Nohara Hiroshi , Yamashita Noriyoshi
Published: August 2016

The 25 highest scored Hecht vaults (G!) performed during the 1995 World Championships were compared with those receiving the 25 lowest scores (G2). Hypotheses were: GI would achieve (a) larger kinetic energy at takeoff from the board and the horse, (b) greater displacements of CM and greater forward body rotation in prellight. (c) greater changes in velocities and angular momentum on horse, (d) more rapid, forceful blocking/pushing off the horse, and (e) greater “amplitude” and better “form” during the post-flight than G2. A 16-mm motion picture camera, operating at 100 Hz. recorded the vaults during the compulsory competition. The results of t tests (p < .005) indicated Gl had (a) larger kinetic energy at takeoff from the board and the horse, (b) greater displacements of CM and greater forward body rotation in pre-flight. (c) greater changes in vertical velocity and angular momentum on the horse. greater vertical impulse of high force and short duration exerted on the horse, and greater “amplitude,” greater backward body rotation, and greater body extension in post-flight than G2. In conclusion, successful performance of the Hecht vault is likely when focus is on sprinting the approach, blocking and pushing off the horse rapidly and vigorously downward, and maintaining the fully extended body position throughout the post-night to display “form” or fish-like body position for a virtuosity bonus point and simultaneously to prepare for a controlled landing on the mat.
Normalized Jerk: A Measure to Capture Developmental Characteristics of Young Girls' Overarm Throwing
Authors: Yan Jin H. , Hinrichs Richard N. , Payne V. Gregory , Thomas Jerry R.
Published: August 2016

This study was designed to examine Ihe developmental differences in the speed and smoothness of arm movement during overarm throwing. The second purpose of this investigation was to evaluate whether jerk is a useful measure in understanding children's overarm throwing. Fifty-one girls, aged 3 to 6 years, voluntarily participated in the study. Each subject threw tennis balls as hard as she could toward a large target on the wall. A 2-camera video system was used to obtain 3-D coordinates of the hand and ball using the DLT algorithm. The variables of velocity and jerk (for the hand and ball) served as the movement outcome measures. The age-associated differences in velocity and normalized jerk (absolute jerk standardized relative to movement time and distance) were examined by ANOVAs. The results supported the hypothesis that the older subjects demonstrated faster and smoother hand movements than their younger counterparts during the forward acceleration phase (from the beginning of forward motion to ball release). In addition, the correlation results indicated thai increased hand movement speed was associated with decreased movement jerk in older subjects, whereas increased hand speed was associated with increased jerk in younger subjects. The findings suggest that examining the jerk parameter (normalized or absolute jerk) is a useful and alternative approach to capture the variance of hand movement execution for children's overarm throwing.
Buoyancy, Gender, and Swimming Performance
Authors: McLean Scott P. , Hinrichs Richard N.
Published: August 2016

This study investigated the relationship of gender and buoyancy to sprint swimming performance. The center of buoyancy (CB) and center of mass (CM) were measured using reaction board principles. Performance was evaluated as the time needed to complete the middle 13.7 m of a 22.9-m sprint for kicking and swimming trials. Nineteen female swimmers (mean ± SD, 21.9 ± 3.2 years) had significantly more body fat (24.1 ± 4.5%) than 13 male swimmers (21.7 ± 4.2 years, 14.8 ± 5.0%). Males swam and kicked significantly faster (p < .01) than females. Percent body fat, upper body strength, the distance between the CB and CM (d), and the buoyant force measured in 3 body positions all met the criteria for entrance into a regression equation. When gender was not controlled in the analysis, these variables accounted for 70% of the variance in swim time (p < .008). When gender was controlled in the analysis, these variables accounted for 45% of the variance in swim time (p = .06). Percent body fat accounted for the largest amount variance in both regression analyses (39%, p < .001; 18%, p = 0.02, respectively). Upper body strength accounted for 14% of the variance in swim time (p = .006) when gender was not controlled but only 4% when gender was controlled (p = .27). The distance d as measured in a body position with both arms raised above the head was the buoyancy factor that accounted for the greatest amount of variance in swim time (6% when gender was not controlled, p = .06, 10%; when gender was controlled, p = .07). Percent body fat, d, and the buoyant force accounted for no significant amount of variance in kick time. These data suggested that a swimmer’s buoyancy characteristics did have a small but important influence on sprint swimming performance.
Addition of an Approach to a Swimming Relay Start
Authors: McLean Scott P. , Holthe Michael J. , Vint Peter F. , Beckett Keith D. , Hinrichs Richard N.
Published: August 2016

Ten male collegiate swimmers (age = 20.2 ± 1.4 years, height = 184.6 ± 5.8 cm, mass = 82.9 ± 9.3 kg) performed 3 swimming relay step starts, which incorporated a one or two-step approach, and a no-step relay start. Time to 10 m was not significantly shorter between step and no-step starts. A double-step start increased horizontal takeoff velocity by 0.2 m/s. A single-step together start decreased vertical takeoff velocity by 0.2 m/s but increased takeoff height by 0.16 m. Subjects were more upright at takeoff by 4°, 2°, and 5° in the double-step, single-step apart, and single-step together starts, respectively, than in the no-step start. Entry angle was steeper by 2°, entry orientation was steeper by 3°, and entry vertical velocity was faster by 0.3 m/s in the single-step together start. Restricting step length by 50% had little effect on step starts with the exceptions that horizontal velocity was significantly reduced by 0.1 m/s in the double-step start and vertical takeoff velocity was increased by 0.2 m/s in the single-step together start. These data suggested that step starts offered some performance improvements over the no-step start, but these improvements were not widespread and, in the case of the double-step start, were dependent on the ability to take longer steps.
Lower Extremity Strength and Coordination Are Independent Contributors to Maximum Vertical Jump Height
Authors: Tomioka Masao , Owings Tammy M. , Grabiner Mark D.
Published: August 2016

We previously reported that lower extremity muscular strength of older adults did not predict success of a balance recovery task. We propose that lower extremity coordination may limit performance independently of lower extremity strength. The present study was conducted to determine the extent to which knee extension strength and hip–knee coordination independently contribute to maximum vertical jump height. Maximum vertical jump height and isometric and isokinetic knee extension strength and power were determined in 13 young adults. Hip–knee coordination during the vertical jump was quantified using relative phase angles. Stepwise nonlinear multiple regression determined the variable set that best modeled the relationship between the dependent variable, maximum vertical jump height, and the independent variables of strength, power, and coordination. The quadratic terms of the normalized knee extension strength at 60 deg·s–1, and the average relative phase during the propulsion phase of the vertical jump, collectively accounted for more than 80% of the shared variance (p = .001). The standardized regression coefficients of the two terms, .59 and .52, respectively (p = .004 and .008), indicated the independence and significance of the contributions of knee extension strength and hip–knee coordination to maximum vertical jump height. Despite the pitfalls of extrapolating these results to older adults performing a balance recovery task, the results are interpreted as supporting the contention that while muscle strength confers a number of functional benefits, the ability to avoid falling as a result of a trip is not necessarily ensured. Increased muscle strength per se can occur in the absence of improved kinematic coordination.
Functional Knee Brace Alters Predicted Knee Muscle and Joint Forces in People with ACL Reconstruction during Walking
Authors: DeVita Paul , Hortobagyi Tibor
Published: August 2016

Functional knee braces used during rehabilitation from injury and surgery to the anterior cruciate ligament (ACL) have been reported to provide a strain-shielding effect on the ACL in healthy people while standing, reduce quadriceps electromyoraphy in ACL-deficient individuals, and alter joint torque patterns in people with ACL reconstruction during walking. These results led to the hypothesis that functional knee braces protect a reconstructed ACL during dynamic activity by reducing the anterior shear load applied to the knee. This hypothesis was tested by investigating the effects of a functional knee brace on lower extremity muscle forces and the anteroposterior shear force at the knee joint during the stance phase of walking in people with ACL reconstruction. Ground reactions and sagittal plane video were recorded from 9 ACL-reconstructed individuals as they walked with and without a functional knee brace, and from 10 healthy people without the functional knee brace. Inverse dynamics were used to calculate the net joint torques in the lower extremity during the stance phase. Hamstrings, quadriceps, and gastrocnemius muscle and knee anteroposterior shear force were then predicted with a sagittal-plane mathematical model. Compared to healthy individuals, those with ACL reconstruction walked with 78% more hamstrings impulse and 19% less quadriceps impulse (bothp< .05). The functional knee brace produced an additional 43% increase in hamstrings impulse and an additional 13% decrease in quadriceps impulse in the ACL group. Peak anterior knee shear force and anterior impulse were 41% lower and 16% lower in ACL vs. healthy individuals, respectively. The functional knee brace further reduced the peak knee shear force and impulse 28% and 19%, respectively, in the ACL group. It was concluded that a functional knee brace protects a reconstructed ACL during walking by altering muscle forces and reducing the anterior shear force applied to the knee joint.
From a One-Legged Vertical Jump to the Speed-Skating Push-off: A Simulation Study
Authors: Bobbert Maarten F. , Houdijk Han , de Koning Jos J. , de Groot Gert
Published: August 2016

To gain a better understanding of push-off mechanics in speed skating, forward simulations were performed with a model comprising four body segments and six muscles. We started with a simulated maximum height one-legged jump, obtained by optimization of muscle stimulation time histories. The simulated jump was very similar to one-legged jumps produced by a human, indicating that the model was realistic. We subsequently studied how performance was affected by introducing four conditions characteristic of speed skating: (a) We changed the initial position from that in jumping to that at the start of the push-off phase in skating. This change was accommodated by a delay in stimulation onset of the plantar flexors in the optimal solution. (b) The friction between foot and ground was reduced to zero. As a result, maximum jump height decreased by 1.2 cm and performance became more sensitive to errors in muscle stimulation. The reason is that without surface friction, the foot had to be prevented from slipping away, which constrained the solution space and reduced the tolerance to errors in stimulation. (c) We introduced the requirement to maintain the upper body in a more or less horizontal position. This change could be accommodated by a delay in stimulation onset of the hamstrings, which inevitably caused a reduction in maximum jump height by 11.6 cm. (d) We increased the effective foot length from 16.5 cm, representative of jumping, to 20.5 cm, representative of skating with klapskates. At the 20.5-cm foot length, rotation of the foot did not start during the buildup of plantar flexion moment as it did at smaller foot lengths, but was delayed until hip and knee extension moments decreased. This caused an unbalanced increase in segment angular velocities and muscle shortening velocities, leading to a decrease in muscle force and muscle work and a further decrease in maximum jump height by approximately 5 cm. Qualitatively, these findings help clarify why and how performance of speed skaters depends on the location of the hinge of their skate.
The Effects of Target Length on the Visual Control of Step Length for Hard and Soft Impacts
Authors: Bradshaw Elizabeth J. , Sparrow W.A.
Published: August 2016

Adjustments to gait were examined when positioning the foot within a narrow target at the end of an approach for two impact conditions, hard and soft. Participants (6 M, 6 F) ran toward a target of three lengths along a 10-m walkway consisting of two marker strips with alternating black and white 0.5-m markings. Five trials were conducted for each target length and impact task, with trials block randomized between the 6 participants of each gender. A 50Hz digital video camera panned and filmed each trial from an elevated position adjacent to the walkway. Video footage was digitized to deduce the gait characteristics. A linear speed/accuracy tradeoff between target length and approach time was found for both impact tasks (hard, r = 0.99, p < 0.01; soft, r = 0.96, p < 0.05). For the hard-impact task, visual control time increased linearly (r = 0.99, p < 0.05) when whole-body approach velocity decreased. Visual control time was unaffected by whole-body approach velocity in the soft-impact task. A constant tau-margin of 1.08 describes the onset of visual control when approaching a target while running, with the control of braking during visual control described by a tau-dot of –0.85. Further research is needed to examine the control of braking in different targeting tasks.
Variability of Stride Characteristics and Joint Coordination among Individuals with Unilateral Patellofemoral Pain
Authors: Heiderscheit Bryan C. , Hamill Joseph , van Emmerik Richard E.A.
Published: August 2016

The purpose of this investigation was to determine whether individuals with patellofemoral pain (PFP) display a reduction in intralimb joint coordination variability compared to nonimpaired persons. In addition, it was hypothesized that the variability of the stride characteristics would be similar between groups. Eight individuals with unilateral PFP and 8 nonimpaired participants ran on a treadmill at a fixed (2.68 m·s–1) and preferred speed while stride characteristics and 3-D kinematics of the bilateral lower extremities were recorded. Intralimb coordination variability was measured using a vector coding technique applied to relative motion plots of various joint couplings. The PFP group displayed greater stride length variability during running at the preferred speed. However, this was not the case during running at the fixed speed. When averaging across the entire stride cycle, coordination variability for all joint couplings was consistent between the two groups. However, further analysis about heel-strike revealed reduced joint coordination variability for the thigh rotation/leg rotation coupling of the PFP group’s injured limb compared to that of the nonimpaired group. With the exception of the transverse plane rotations at heel-strike, it would appear that the level of pain experienced by the PFP participants may not be great enough to produce a change in the intralimb coordination patterns during running.
Determining Subject-Specific Torque Parameters for Use in a Torque-Driven Simulation Model of Dynamic Jumping
Authors: King Mark A. , Yeadon Maurice R.
Published: August 2016

This paper describes a method for defining the maximum torque that can be produced at a joint from isovelocity torque measurements on an individual. The method is applied to an elite male gymnast in order to calculate subject-specific joint torque parameters for the knee joint. Isovelocity knee extension torque data were collected for the gymnast using a two-repetition concentric-eccentric protocol over a 75° range of crank motion at preset crank angular velocities ranging from 20 to 250°s–1. During these isovelocity movements, differences of up to 35° were found between the angle of the dynamometer crank and the knee joint angle of the participant. In addition, faster preset crank angular velocities gave smaller ranges of isovelocity motion for both the crank and joint. The simulation of an isovelocity movement at a joint angular velocity of 150°s–1 showed that, for realistic series elastic component extensions, the angular velocity of the joint can be assumed to be the same as the angular velocity of the contractile component during most of the isovelocity trial. Fitting an 18-parameter exponential function to experimental isovelocity joint torque/ angle/ angular velocity data resulted in a surface that was well behaved over the complete range of angular velocities and within the specified range of joint angles used to calculate the surface.
Soft Tissue Motion during Impacts: Their Potential Contributions to Energy Dissipation
Authors: Pain Matthew T.G. , Challis John H.
Published: August 2016

The aims of this study were to quantify intrasegmental motion using an array of 28 surface-mounted markers to examine frequency and amplitude measurements of the intrasegmental motion to calculate forces and energy transfer; and to show that the underlying muscles are a major contributor to the skin marker motion. One participant performed 27 trials under three conditions in which his forearm was struck against a solid object fixed to a force plate while the locations of the markers were recorded at 240 Hz. For impacts with equal peak forces, the muscle tension significantly affected the amount of intrasegmental motion. Tensing the arm reduced the intrasegmental motion by 50%. The quadrilateral sectors defined by the markers changed in area by 11% with approximately equal motion in the vertical and horizontal direction. The maximum linear marker motion was 1.7 cm. The intrasegmental motion had distinct frequency components around 14 and 20 Hz. Soft tissue deformation could account for 70% of the energy lost from the forearm during these impacts. The study has demonstrated the important role that intrasegment soft tissue motion can have on the kinetics of an impact.
Practical Use of Airborne Simulation in a Release-Regrasp Skill on the High Bar
Authors: Holvoet Patrice , Lacouture Patrick , Duboy Jacques
Published: August 2016

The aim of this study was to objectively predict individual improvements in a release-regrasp tkatchev skill. The prediction was based on a kinematic analysis of failed and successful trials. The modification of release conditions, and the correction of hip and shoulder joint motions during the aerial phase of failed trials, were determined by considering the successful trials as target executions. Computer simulations were used to confirm the effect of the corrected parameters on the flight trajectory and angular motion of the body over the bar. The results indicated that when time of release is initiated earlier, this presents a major problem the gymnast must overcome in order to grasp the bar. Moreover, the moment when the body’s center of gravity is vertically above the bar represents a critical instant for the gymnast in initiating the hip and shoulder movements. The rotation motion analysis of the segments indicated that the stabilization motion of the upper limbs could be a good strategy for improving the failed tkatchev. This study showed that simple computer simulation using hypothetical data based upon real data could be an effective tool for improving acrobatic skills.
A Method for Measuring Euler Rotation Angles and Helical Axis of Upper Arm Motion
Authors: LaScalza Suzanne , Gallo Linda N. , Carpenter James E. , Hughes Richard E.
Published: August 2016

Clinical observation suggests that shoulder pathologies such as rotator cuff disorders and shoulder instability may alter the normal shoulder rhythm or relative motions of the structures comprising the shoulder girdle. The purpose of this study was to assess the accuracy of using a skin-mounted humeral cuff that could be used in vivo to determine Euler rotation angles and the helical axis of motion (HAM) during upper extremity movements. An in vitro model was used to compare the kinematics determined from the externally applied humeral cuff to the kinematics measured directly from the humerus. The upper extremities of five cadavers were moved through several humerus and forearm motion trials. Measurements from the humeral cuff were compared directly to the bone measurements for all trials to determine the accuracy of the Euler rotation angles. In evaluating the HAM, the orientation, location, and magnitude of rotation were compared either to the bone measurements or to the known rotational axis of the testing fixture. Euler rotation angles and the helical axis of motion determined by the measurements taken from the skin-mounted humeral cuff were very similar to those using the measurements from the bone-mounted sensor. The humeral cuff was shown to provide a viable, noninvasive method for determining the Euler rotation angles and helical axis of motion during 3-D humeral movements. The validation makes the humeral cuff a valuable tool for examining the effect of shoulder pathologies on the kinematics of the upper extremity.
The Effects of Wind and Altitude in the 200-m Sprint
Authors: Quinn Mike D.
Published: August 2016

A mathematical model is used to determine the effect of wind resistance and altitude on 200-m race times. The model is used to simulate the effect of different wind speeds, wind directions, and lane allocation in the 200-m sprint. For the 200-m event there is a single wind gauge recording only the wind’s component velocity in the straight, and not the wind direction. For record purposes the wind reading should not exceed 2 m/s. It is evident that for the same official wind reading, an athlete may face vastly different conditions. The model estimates that for the same wind reading, the prevailing conditions can produce a time difference of as much as 0.5 s. Results indicate that many legal performances in the 200-m are currently ruled out for record purposes. Some performances which are officially wind-assisted have in fact been hindered by an overall head wind when it is averaged throughout the race. Conversely, some performances which are run into a head wind in the straight have benefited from an overall tail wind. We estimate that, on average, for a 2-m/s wind blowing down the straight, the 200-m runner benefits from an overall tail wind of only 0.95 m/s. The lower air density at an altitude of 1,500 meters produces an advantage of 0.11 s in the 200-m, which equates to a 2-m/s tail wind at sea level blowing directly down the straight. Correction estimates are provided for the combined effect of both wind and altitude in 200-m races. A new all-time world top five ranking list for men and women is produced for the 200-m event, corrected for wind and altitude effects.
Classification and Comparison of Biomechanical Response Strategies for Accommodating Landing Impact
Authors: James C. Roger , Bates Barry T. , Dufek Janet S.
Published: August 2016

The purposes of this study were to (a) present a theoretical model to explain the methods by which individuals accommodate impact force in response to increases in an applied stressor, (b) use the model and a correlation procedure to classify a sample of individuals based on their observed response patterns, and (c) statistically evaluate the classification process. Ten participants performed landings from three heights while video and force platform data were being collected. Magnitudes of impact-force characteristics from ground reaction force and lower extremity joint moments were evaluated relative to changes in landing momentum. Correlation between impact force and landing momentum was used to classify participant responses into either a positive or negative biomechanical strategy, as defined by the model. Positive and negative groups were compared using the Mann-Whitney U test. Results indicated that all responses fit within the categories defined by the model. Some individuals preferred positive strategies while others preferred negative ones depending on the specific variable. Only one participant consistently exhibited the negative strategy for all variables. Positive and negative groups were determined to be statistically different, p ≤ 0.05, for 61% of the comparisons, suggesting actual differences between groups. The proposed model appeared robust and accounted for all responses in the current experiment. The model should be evaluated further using landing and other impact activities; it should be refined and used to help researchers understand individual impact-response strategies in order to identify those who may be at risk for impact related injuries.
Optimization Model Estimates of Trunk Muscle Forces Do Not Correlate with EMG Activity of Females as Well as Males
Authors: McMulkin Mark L. , Woldstad Jeffrey C. , Hughes Richard E.
Published: August 2016

Biomechanical optimization models are often used to estimate muscular and intervertebral disc forces during physical exertions. The purpose of this study was to determine whether an optimization-based biomechanical model predicts torso muscular activity of males and females equally well. The Minimum Intensity Compression (MIC) model, which has been extensively applied in industrial ergonomic task analysis, was used to estimate muscle forces for 3D moments. Participants (6 M, 6 F) performed 18 isometric exertions resisting 3D L3/L4 moments while electromyographic (EMG) activity was recorded for 8 muscles. Overall, model force estimates correlated better with male EMG activity (R2 = 0.43) than with female EMG activity (R2 = 0.33). Model force estimates of 4 muscles (LRA, RRA, REO, and RES) correlated better with male EMG activity than with female EMG. We conclude that trunk muscle forces estimated by current biomechanical modeling do not correlate equally well to male and female EMG activity. Future research needs to address validation or improvement of biomechanical trunk models for females.
Identifying Heel Contact and Toe-Off Using Forceplate Thresholds with a Range of Digital-Filter Cutoff Frequencies
Authors: Tirosh Oren , Sparrow W.A.
Published: August 2016

Analysis of human gait requires accurate measurement of foot-ground contact, often determined using either foot-ground reaction force thresholds or kinematic data. This study examined the differences in calculating event times across five vertical force thresholds and validated a vertical acceleration-based algorithm as a measure of heel contact and toe-off. The experiment also revealed the accuracy in determining heel contact and toe-off when raw displacement/time data were smoothed using a range of digital filter cutoff frequencies. Four healthy young participants completed 10 walking trials: 5 at normal speed (1.2 m/s) and 5 at fast speed (1.8 m/s). A 3D optoelectric system was synchronized with a forceplate to measure the times when vertical force exceeded (heel contact) or fell below (toe-off) 10, 20, 30, 40, and 50 N. These were then compared and subsequently used to validate an acceleration-based method for calculating heel contact and toe-off with the displacement/time data filtered across a range of four cutoff frequencies. Linear regression analyses showed that during both normal and fast walking, any force threshold within 0 to 50 N could be used to predict heel-contact time. For estimating toe-off low force thresholds, 10 N or less should be used. When raw data were filtered with the optimal cutoff frequency, the absolute value (AbsDt) of the difference between the forceplate event times obtained using a 10-N threshold and the event times of heel contact and toe-off using the acceleration-based algorithms revealed average AbsDt of 10.0 and 16.5 ms for normal walking, and 7.4 and 13.5 ms for fast walking. Data smoothing with the non-optimal cutoff frequencies influenced the event times computed by the algorithms and produced greater AbsDt values. Optimal data filtering procedures are, therefore, essential for ensuring accurate measures of heel contact and toe-off when using the acceleration-based algorithms.
Intent-Related Differences in Surface EMG of Maximum Eccentric and Concentric Contractions
Authors: Grabiner Mark D. , Owings Tammy M.
Published: August 2016

For this study it was hypothesized that when participants intended to perform a maximum voluntary concentric (or eccentric) contraction but had an eccentric (or concentric) contraction imposed upon them, the initial EMG measured during the isometric phase preceding the onset of the dynamometer motion would reflect the intended contraction condition. The surface EMG of the vastus lateralis muscle was measured in 24 participants performing isokinetic concentric and eccentric maximum voluntary knee extensor contractions. The contractions were initiated from rest and from the same knee flexion angle and required the same level of external force to trigger the onset of dynamometer motion. Vastus lateralis EMG were quantified during the isometric phase preceding the onset of the dynamometer motion. When participants intended to perform a concentric contraction but had an eccentric contraction imposed upon them, the initial EMG resembled that of a concentric contraction. When they intended to perform an eccentric contraction but had a concentric contraction imposed upon them, the initial EMG resembled that of an eccentric contraction. Overall, the difference between concentric and eccentric contractions observed during the period of the initial muscle activation implies that descending signals include information that distinguishes between eccentric and concentric contractions.
A Method for Assessing the Overall Impact Performance of Riot Helmets
Authors: Dionne Jean-Philippe , Maach Ismail El , Shalabi Ahmed , Makris Aris
Published: August 2016

The objective of the present paper is to investigate the overall impact performance of various riot helmets in a comparative study. The National Institute of Justice (NIJ-0104.02) and the Canadian Standards Association (CSA-Z611-02) standards regulate the use of riot helmets in North America. Both sets of standards have a number of requirements for impact performance. Impact tests carried out with the use of a drop tower apparatus compliant with NIJ test protocols demonstrated large differences in impact attenuation level among the helmets from six manufacturers in terms of frontal and lateral impacts to the shell, and face-shield deflection. For instance, the impact energy yielding a head form acceleration of 300 g’s was measured for each helmet for frontal impacts on the helmet shell. Values ranging from 69 J up to 171 J were obtained. The energy levels of typical crowd-control threats, e.g., baton blows and projectiles, were quantified and compared with the impact energy values used in the standards. It is observed that the NIJ face-shield deflection requirement is low as compared to actual riot threats, whereas the CSA requirements are more in line with these threats. A novel method was devised to objectively assign a global impact performance score to each helmet. This method takes into account the frontal and lateral impacts to the shell as well as the face-shield deflection tests. It is based on the directional origin of the threat and the geometry of the helmets (frontal percentage area of the visor). From these global performance scores, it is possible to obtain a ranking of the various riot helmets used in the present comparative study. Based on the analysis of the global scores, it was found that appropriate protection of the face (through an impact resistant visor) is the key feature for a helmet that will be used in riot environments.
Analysis of a Network for Finger Interaction during Two-Hand Multi-Finger Force Production Tasks
Authors: Goodman Simon R. , Latash Mark L. , Li Sheng , Zatsiorsky Vladimir M.
Published: August 2016

This study involved an optimization, numerical analysis of a network for two-hand multi-finger force production, analogous in its structure to the double-representation mirror image (DoReMi) network suggested earlier based on neurophysiological data on cortical finger representations. The network accounts for phenomena of enslaving (unintended finger force production), force deficit (smaller force produced by a finger in multi-finger tasks as compared to its single-finger task), and bilateral deficit (smaller forces produced in two-hand tasks as compared to one-hand tasks). Matrices of connection weights were computed, and the results of optimization were compared to the experimental data on finger forces during one- and two-hand maximal force production (MVC) tasks. The network was able to reproduce the experimental data in two-hand experiments with high accuracy (average error was 1.2 N); it was also able to reproduce findings in one-hand multi-finger MVC tasks, which were not used during the optimization procedure, although with a somewhat higher error (2.8 N). Our analysis supports the feasibility of the DoReMi network. It suggests that within-a-hand force deficit and bilateral force deficit are phenomena of different origins whose effects add up. Is also supports a hypothesis that force deficit and enslaving have different neural origins.
Equinus Deformity as a Compensatory Mechanism for Ankle Plantarflexor Weakness in Cerebral Palsy
Authors: Hampton David A. , Hollander Kevin W. , Engsberg Jack R.
Published: August 2016

A theory for equinus gait in cerebral palsy (CP) is that the strong plantarflexors prevent the weak dorsiflexors from achieving dorsiflexion, thereby causing the ankle to be in a plantarflexed position. Recent work has indicated that both the ankle dorsiflexors and plantarflexors are weak. The purpose of this research was to theoretically and experimentally demonstrate that equinus deformity gait could be a compensatory strategy for plantarflexor weakness. It was hypothesized that children with CP utilize an equinus position during gait as a consequence of their weakness. A two-dimensional, sagittal plane model estimating plantarflexor forces through the Achilles tendon was developed. Five able-bodied (AB) children were tested utilizing heel-toe and progressively increasing toe walking strategies. Four children with CP were tested as they walked using their equinus gait. Results demonstrated that AB children assuming the toe walking stance progressively reduced the plantarflexor force when compared to their heel-toe walking trials. However, their toe walking strategy could not reduce the plantarflexor force level to that of the children with CP during the gait cycle. It was concluded that the equinus deformity posture complemented the CP children's plantarflexor weakness. Therefore, by implementing a concomitant strategy to maintain a reduced force state, equinus deformity could be used as a compensatory mechanism for individuals with plantarflexor weakness.
3-D Kinematics Using Moving Cameras. Part 1: Development and Validation of the Mobile Data Acquisition System
Authors: Lafontaine Dany , Lamontagne Mario
Published: August 2016

Many human activities, particularly sporting skills, occur over large distances. But technical limitations have forced biomechanists to conduct studies only on portions of such skills. In this paper we present the design and validation of a mobile data collection system composed of a camera cart that allows the tracking of athletes along a larger portion of their movements. A key feature of this system is that it requires only a small field of view to record and analyze joint motions. The validation of this method was conducted with three approaches. For all approaches, intermarker distances obtained from real measures were compared to those obtained from digitized video data. In all three experiments, the results proved to be within the accepted error range of 5%. The net differences between measured values and digitized values ranged from 0.8 to 3 mm, while the relative errors ranged from 0.2 to 6%. This first experimentation using a mobile camera array to collect and reconstruct biomechanical data has proven to be valid and worth pursuing for recording and analyzing ice hockey skating.
In Vitro Measurements of First and Second Tarsometatarsal Joint Stiffness
Authors: Fauth Andrew R. , Hamel Andrew J. , Sharkey Neil A.
Published: August 2016

This study involved a biomechanical examination of the first and second tar-sometatarsal (TMT) joints. In the in vitro testing protocol, physiologic joint moments were applied to the first and second TMT joints of 10 cadaver specimens, which had been dissected to yield only the midfoot components comprising the tarsals, metatarsals, and associated ligaments. The isolated joints were placed in a 37 °C water bath and were independently cycled into and out of dorsiflexion, while angular displacement and resultant joint moments were collected. The specimens were sequentially cycled between zero and peak moment levels of 2.5, 5.0, 7.5, and 10 Nm, after which mean moment-angle curves were plotted for each TMT joint at each loading condition. Least-squares curve-fitting procedures, employing a root mean square error threshold of 0.005 Nm, were used to describe the average overall moment vs. angle relationship of each joint. Curves for the first and second TMT joints exhibited similar behavior. The joints displayed reasonably constant stiffness at low angles of dorsiflexion, followed by rapidly increasing stiffness at higher angles of dorsiflexion. These data provide new insight into the behavior of the TMT joints under load and are valuable for use in numerical models of the foot, as well as in the understanding and treatment of certain foot pathologies.
Application of Taguchi's Design of Experiments to the Study of Biomechanical Systems
Authors: Wang Nenzi , Liu Yen-Hsiu
Published: August 2016

An efficient global optimization procedure is presented by using Taguchi's design of experiments (TDE) as a means for undertaking biomechanical studies that rely on experimentations. The proposed TDE is a systematic method of fractional factorial designs for conducting experiments with many independent variables. The approach can provide a step-by-step means for predicting the results of a comparative full factorial design only with a small number of tests. In this study a three-level, four-variable heel-toe running model, and a two-level, seven-variable bicycle example were examined to show the capability and robustness of TDE. In the process of the analysis, the orthogonal array and signal-to-noise ratio analysis of TDE were used to set up the trial conditions and analyze the results. It is shown that in the heel-toe running analyses the TDE successfully predicted the optimum sets of variables with 89% fewer trials than the full factorial design. The reduction in number of trials in the bicycle example is 94%. As a result, the use of TDE analysis to replace a full factorial analysis can considerably reduce the number of trials and still provide a useful outcome in many multifactor biomechanical studies.
A Nonlinear Dynamics Approach to Human Movement
Authors: Van Emmerik Richard E.A. , Rosenstein Michael T. , McDermott William J. , Hamill Joseph
Published: August 2016

Nonlinear dynamics and dynamical systems approaches and methodologies are increasingly being implemented in biomechanics and human movement research. Based on the early insights of Nicolai Bernstein (1967), a significantly different outlook on the movement control “problem” over the last few decades has emerged. From a focus on relatively simple movements has arisen a research focus with the primary goal to study movement in context, allowing the complexity of patterns to emerge. The approach taken is that the control of multiple degrees-of-freedom systems is not necessarily more difficult or complex than that of systems only comprising a few degrees of freedom. Complex patterns and dynamics might not require complex control structures. In this paper we present a tutorial overview of the mathematical underpinnings of nonlinear dynamics and some of its basic analysis tools. This should provide the reader with a basic level of understanding about the mathematical principles and concepts underlying pattern stability and change. This will be followed by an overview of dynamical systems approaches in the study of human movement. Finally, we discuss recent progress in the application of nonlinear dynamical techniques to the study of human locomotion, with particular focus on relative phase techniques for the assessment of coordination.
Modeling Deformation Behavior of the Baseball
Authors: Nicholls Rochelle Llewelyn , Miller Karol , Elliott Bruce C.
Published: August 2016

Regulating ball response to impact is one way to control ball exit velocity in baseball. This is necessary to reduce injuries to defensive players and maintain the balance between offense and defense in the game. This paper presents a model for baseball velocity-dependent behavior. Force-displacement data were obtained using quasi-static compression tests to 50% of ball diameter (n = 70 baseballs). The force-displacement curves for a very stiff baseball (Model B) and a softer type (Model C) were characterized by a Mooney-Rivlin model using implicit finite element analysis (ANSYS software, version 6.1). Agreement between experimental and numerical results was excellent for both Model B (C10 = 0, C01 = 3.7e6 Pa) and Model C (C10 = 0, C01 = 2.6e6 Pa). However, this material model was not available in the ANSYS/LSDYNA explicit dynamic software (version 6.1) used to quantify the transient behavior of the ball. Therefore the modeling process was begun again using a linear viscoelastic material. G∞, the long-term shear modulus of the material, was determined by the same implicit FEA procedure. Explicit FEA was used to quantify the time-dependent response of each ball in terms of instantaneous shear modulus (G0) and a decay term (β). The results were evaluated with respect to published experimental data for the ball coefficient of restitution at five velocities (13.4–40.2 ms–1) and were in agreement with the experimental values. The model forms the basis for future research on baseball response to impact with the bat.
Reliability of an Individually Molded Shank Shell for Measuring Tibial Transverse Rotations during the Stance Phase of Walking
Authors: Levinger Pazit , Gilleard Wendy , Coleman Cliff
Published: August 2016

Use of a shank shell has been shown to estimate tibial transverse rotations better than skin-mounted markers. However, the day-to-day reliability of the transverse tibial rotations using an individually molded shank shell has not been previously investigated. This study examined the between-tests and trials reliability of an individually molded shank shell for measuring peak tibial internal and external rotations, time of peak values, and tibia range of motion during 5 walking trials. The trial-to-trial reliability of tibial transverse rotations was measured in 14 healthy individuals while the test-retest reliability was measured in 10 persons on two occasions. Trial-to-trial reliability for peak transverse rotations, time of peak values, and tibia range of motion ranged from ICC (3,1) 0.59–0.95. The PCA between trials showed that 88–99% of values were within 3° of agreement. Test-retest reliability for peak rotations, tibia range of motion, and time of peak values ranged from ICC (3,1) 0.70–0.89 with SEM 1.6–2.21°, 0.021%, and 0.034%, respectively. The PCA between tests showed that 70–100% of values were within 3° of agreement. The use of an individually molded shell and the close attachment of the shank shell to the individual's shank resulted in reliable test-retest and trial-to-trial data.
The Margin for Error When Releasing the Asymmetric Bars for Dismounts
Authors: Hiley Michael J. , Yeadon Maurice R.
Published: August 2016

It has previously been shown that male gymnasts using the “scooped” giant circling technique were able to flatten the path followed by their mass center, resulting in a larger margin for error when releasing the high bar (Hiley & Yeadon, 2003a). The circling technique prior to performing double layout somersault dismounts from the asymmetric bars in women's artistic gymnastics appears to be similar to the “traditional” technique used by some male gymnasts on the high bar. It was speculated that as a result the female gymnasts would have margins for error similar to those of male gymnasts who use the traditional technique. However, it is unclear how the technique of the female gymnasts is affected by the need to avoid the lower bar. A 4-segment planar simulation model of the gymnast and upper bar was used to determine the margins for error when releasing the bar for 9 double layout somersault dismounts at the Sydney 2000 Olympics. The elastic properties of the gymnast and bar were modeled using damped linear springs. Model parameters, primarily the inertia and spring parameters, were optimized to obtain a close match between simulated and actual performances in terms of rotation angle (1.2°), bar displacement (0.011 m), and release velocities (<1%). Each matching simulation was used to determine the time window around the actual point of release for which the model had appropriate release parameters to complete the dismount successfully. The margins for error of the 9 female gymnasts (release window 43–102 ms) were comparable to those of the 3 male gymnasts using the traditional technique (release window 79–84 ms).
Lower Extremity Coupling Parameters during Locomotion and Landings
Authors: Tillman Mark D. , Hass Chris J. , Chow John W. , Brunt Denis
Published: August 2016

During ballistic locomotion and landing activities, the lower extremity joints must function synchronously to dissipate the impact. The coupling of subtalar motion to tibial and knee rotation has been hypothesized to depend on the dynamic requirements of the task. This study was undertaken to look for differences in the coupling of 3-D foot and knee motions during walking, jogging, and landing from a jump. Twenty recreationally active young women with normal foot alignment (as assessed by a licensed physical therapist) were videotaped with high-speed cameras (250 Hz) during walking, jogging, hopping, and jumping trials. Coupling coefficients were compared among the four activities. The ratio of eversion to tibial rotation increased from the locomotion to the landing trials, indicating that with the increased loading demands of the activity, the requirements of foot motion increased. However, this increased motion was not proportionately translated into rotation of the tibia through the subtalar joint. Furthermore, the ratio of knee flexion to knee internal rotation increased significantly from the walking to landing trials. Together these findings suggest that femoral rotation may compensate for the increase in tibial rotation as the force-dissipating demands of the task increase. The relative unbalance among the magnitude of foot, tibial, and knee rotations observed with increasing task demands may have direct implications on clinical treatments aimed at reducing knee motion via controlling motion at the foot during landing tasks.