bluuebunny/crossref_metadata_2025 huggingface dataset:
Contribution of Series Elasticity in Human Cyclic Heel-Raise Exercise
Authors: Nagano Akinori , Fukashiro Senshi , Komura Taku
Published: August 2016

Contribution of series elasticity of the human mm. triceps surae in cyclic heel-raise exercise (similar to hopping but the feet do not leave the floor) was examined via computer modeling and simulation. A two-dimensional skeletal model of the human body was constructed. Upright posture was maintained throughout the simulation to prevent the model from falling. A mathematical representation of the mm. triceps surae was implemented in the skeletal model. The muscle was activated by the neural activation input signal with a time resolution of 0.050 sec. Cyclic heel-raise exercises of cycle duration ranging from 0.300 sec to 0.900 sec, corresponding to the motion frequency of 200 to 66.7 cycles/min, were generated using an optimization approach. The goal of the numerical optimization was to generate cyclic motions with as much range of motion as possible. As a result, realistic heel-raise motions were generated with the range of motion between 0.0023 m (cycle duration = 0.300 sec) and 0.0414 m (cycle duration = 0.900 sec). It was found that contribution of the series elasticity in positive mechanical work output of the muscle-tendon complex during the pushoff phase (from the lowest position to the termination of a cycle) increased as motion frequency increased (3% at 66.7 cycles/min to 47% at 200 cycles/min). Relatively higher muscle activation was found during the downward moving phase when the motion frequency was higher. These tendencies are consistent with the findings reported in preceding studies involving experimental animals as well as human participants. It is suggested that series elasticity plays an integral role in the generation of cyclic human motions.
A Computational Technique for Determining the Ground Reaction Forces in Human Bipedal Stance
Authors: Audu Musa L. , Kirsch Robert F. , Triolo Ronald J.
Published: August 2016

Our long-term goal is to use a musculoskeletal modeling approach for developing controller algorithms to restore standing balance to individuals with lower extremity paralysis using functional electrical stimulation. This paper describes a technique that facilitates this approach by avoiding the numerical problems associated with modeling the closed kinematic chain formed by the two lower extremities and the ground while standing. Specifically, we propose an optimization technique to estimate the magnitude and origin of the ground reaction force (GRF) vector on one of the feet, resulting in an equivalent open-chain formulation. Using this technique, we performed a series of inverse dynamic computations to determine the GRF and center of pressure (COP) values for five standing postures: neutral, neutral with forward lean, neutral with backward lean, wide, and tandem. The optimization procedure elicited force results that satisfy equilibrium and result in COP locations that are consistent and physically reasonable.
Triathlon Wet Suit and Technical Parameters at the Start and End of a 1500-m Swim
Authors: Perrier David , Monteil Karine
Published: August 2016

The aim of this study was to determine the effect of wearing a triathlon wet suit on the technical parameters of the front crawl stroke. Eight highly trained male triathletes were filmed with underwater camcorders during two 1500-m swim tests: one with a wet suit (WS) and the other with a standard suit (SS). Two conditions were considered: Condition I (CI) and Condition XV (CXV), representing the 1st and the 15th 100-m, respectively. Views were synchronized and digitized using kinematic analysis software (Schleihauf, 1994) to obtain 3-D coordinates of the anatomical landmarks of the body. Results showed that the wet suit and duration of the exercise significantly influenced stroke parameters. The swim with WS was characterized by greater stroke length and a progressive increase in stroke frequency, resulting from a more extended elbow position during the stroke and from a decrease in the absolute and relative times of the propulsive phase. These changes indicated more efficient upper limb action. The duration of exercise modified the swim with WS and SS. The loss of velocity observed in CXV was related to a decrease in stroke length, or more precisely a reduction in lever arm length during the aquatic phase, insufficiently offset by a slight increase in stroke frequency. These two motor responses, a less extended elbow position and a stroke frequency increase, emerged as an easier motor solution for coping with the effect of fatigue. This solution could be regarded as an adaptation to the duration of the exercise.
Reduction of Lower Limb Model Indeterminacy by Force Redundancy in Sit-to-Stand Motion
Authors: Mak Margaret K.Y. , Levin Oron , Mizrahi Joseph , Hui-Chan Christina W.Y.
Published: August 2016

Calculation of joint torques during the rising phase of sit-to-stand motion is in most cases indeterminate, due to the unknown thighs/chair reaction forces in addition to the other sources of uncertainties such as joint positioning and anthropometric data. In the present study we tested the reliability of computation of the joint torques from a five-segment model; we used force plate data of thighs/chair and feet/ground reaction forces, in addition to kinematic measurements. While solving for joint torques before and after seat-off, differences between model solutions and measured data were calculated and minimized using an iterative algorithm for the reestimation of joint positioning and anthropometric properties. The above method was demonstrated for a group of six normal elderly persons.
Wobbling Mass Influence on Impact Ground Reaction Forces: A Simulation Model Sensitivity Analysis
Authors: Pain Matthew T.G. , Challis John H.
Published: August 2016

Wobbling mass models have been used to gain insight into joint loading during impacts. This study investigated the sensitivity of a wobbling mass model of landing from a drop to the model's parameters. A 2-D wobbling mass model was developed. Three rigid linked segments designed to represent the skeleton each had a second mass attached to them, via two translational nonlinear spring dampers, representing the soft tissue. Model parameters were systematically varied one at a time and the effect this had on the peak vertical ground reaction force and segment kinematics was examined. Model output showed low sensitivity to most model parameters but was sensitive to the timing of joint torque initiation. Varying the heel pad stiffness in the range of stiffness values reported in the literature had the largest influence on peak vertical ground reaction force. The analysis indicated that the more proximal body segments had a lower influence on peak vertical ground reaction force per unit mass than the segments nearer the contact point. Model simulations were relatively insensitive to variations in the properties of the connection between wobbling masses and the skeleton. If the goal is to examine the effects of wobbling mass on the system, this insensitivity is an advantage, with the proviso that estimates for the other model parameters and joint torque activation timings lie in a realistic range. If precise knowledge about the motion of the wobbling mass is of interest, however, this calls for more experimental work to precisely determine these model parameters.
A Simple Method for Measuring Stiffness during Running
Authors: Morin Jean-Benoît , Dalleau Georges , Kyröläinen Heikki , Jeannin Thibault , Belli Alain
Published: August 2016

The spring-mass model, representing a runner as a point mass supported by a single linear leg spring, has been a widely used concept in studies on running and bouncing mechanics. However, the measurement of leg and vertical stiffness has previously required force platforms and high-speed kinematic measurement systems that are costly and difficult to handle in field conditions. We propose a new “sine-wave” method for measuring stiffness during running. Based on the modeling of the force-time curve by a sine function, this method allows leg and vertical stiffness to be estimated from just a few simple mechanical parameters: body mass, forward velocity, leg length, flight time, and contact time. We compared this method to force-platform-derived stiffness measurements for treadmill dynamometer and overground running conditions, at velocities ranging from 3.33 m·s–1to maximal running velocity in both recreational and highly trained runners. Stiffness values calculated with the proposed method ranged from 0.67% to 6.93% less than the force platform method, and thus were judged to be acceptable. Furthermore, significant linear regressions (p< 0.01) close to the identity line were obtained between force platform and sine-wave model values of stiffness. Given the limits inherent in the use of the spring-mass model, it was concluded that this sine-wave method allows leg and stiffness estimates in running on the basis of a few mechanical parameters, and could be useful in further field measurements.
Dynamics of the In-Run in Ski Jumping: A Simulation Study
Authors: Ettema Gertjan J.C. , Bråten Steinar , Bobbert Maarten F.
Published: August 2016

A ski jumper tries to maintain an aerodynamic position in the in-run during changing environmental forces. The purpose of this study was to analyze the mechanical demands on a ski jumper taking the in-run in a static position. We simulated the in-run in ski jumping with a 4-segment forward dynamic model (foot, leg, thigh, and upper body). The curved path of the in-run was used as kinematic constraint, and drag, lift, and snow friction were incorporated. Drag and snow friction created a forward rotating moment that had to be counteracted by a plantar flexion moment and caused the line of action of the normal force to pass anteriorly to the center of mass continuously. The normal force increased from 0.88G on the first straight to 1.65G in the curve. The required knee joint moment increased more because of an altered center of pressure. During the transition from the straight to the curve there was a rapid forward shift of the center of pressure under the foot, reflecting a short but high angular acceleration. Because unrealistically high rates of change of moment are required, an athlete cannot do this without changing body configuration which reduces the required rate of moment changes.
The Efficacy of a Pneumatic Compression Device in the Treatment of Plantar Fasciitis
Authors: Kavros Steven J.
Published: August 2016

Plantar fasciitis is a common foot disorder that affects more than two million Americans each year. Conservative management of plantar fasciitis is the first line of treatment by the medical specialist who frequently encounters this common foot complaint. In this study, 50 patients with plantar fasciitis of 4 weeks duration but less than 12 weeks were randomized into two groups. One group of 25 patients used the AirHeel (Aircast, Inc.) and the second group of 25 used the 1st Step prefabricated foot insert (Wrymark, Inc). Standardized weight-bearing radiographs were obtained in order to categorize the foot type: normal arch, pes planus, or pes cavus. Patients were initially evaluated and at 12 weeks they returned for a subsequent visit. The contact area of the foot with the AirHeel and 1st Step insert were similar, an increase of 27% and 26%, respectively, over the contact area barefoot. There was a noted difference in force reduction with the two devices. The AirHeel reduced the midstance force by 20.19%, as compared to the 1st Step insert which showed a 1.03% increase in midstance force. Patients with a higher initial pain score seemed to respond better initially to the AirHeel (p= 0.015) than the 1st Step insert (p= 0.035). This study demonstrates the benefits of offloading the foot at midstance with two devices to relieve the discomfort associated with plantar fasciitis. The Aircast AirHeel is a new modality for dynamic, functional treatment of proximal plantar fasciitis.
Contribution of Muscle Series Elasticity to Maximum Performance in Drop Jumping
Authors: Böhm Harald , Cole Gerald K. , Brüggemann Gert-Peter , Ruder Hanns
Published: August 2016

The contribution of muscle in-series compliance on maximum performance of the muscle tendon complex was investigated using a forward dynamic computer simulation. The model of the human body contains 8 Hill-type muscles of the lower extremities. Muscle activation is optimized as a function of time, so that maximum drop jump height is achieved by the model. It is shown that the muscle series elastic energy stored in the downward phase provides a considerable contribution (32%) to the total muscle energy in the push-off phase. Furthermore, by the return of stored elastic energy all muscle contractile elements can reduce their shortening velocity up to 63% during push-off to develop a higher force due to their force velocity properties. The additional stretch taken up by the muscle series elastic element allows only m. rectus femoris to work closer to its optimal length, due to its force length properties. Therefore the contribution of the series elastic element to muscle performance in maximum height drop jumping is to store and return energy, and at the same time to increase the force producing ability of the contractile elements during push-off.
Relationship between Hip and Knee Strength and Knee Valgus during a Single Leg Squat
Authors: Claiborne Tina L. , Armstrong Charles W. , Gandhi Varsha , Pincivero Danny M.
Published: August 2016

The purpose of this study was to determine the relationship between hip and knee strength, and valgus knee motion during a single leg squat. Thirty healthy adults (15 men, 15 women) stood on their preferred foot, squatted to approximately 60 deg of knee flexion, and returned to the standing position. Frontal plane knee motion was evaluated using 3-D motion analysis. During Session 2, isokinetic (60 deg/sec) concentric and eccentric hip (abduction/adduction, flexion/extension, and internal/external rotation) and knee (flexion/extension) strength was evaluated. The results demonstrated that hip abduction (r2 = 0.13), knee flexion (r2 = 0.18), and knee extension (r2 = 0.14) peak torque were significant predictors of frontal plane knee motion. Significant negative correlations showed that individuals with greater hip abduction (r = –0.37), knee flexion (r = –0.43), and knee extension (r = –0.37) peak torque exhibited less motion toward the valgus direction. Men exhibited significantly greater absolute peak torque for all motions, excluding eccentric internal rotation. When normalized to body mass, men demonstrated significantly greater strength than women for concentric hip adduction and flexion, knee flexion and extension, and eccentric hip extension. The major findings demonstrate a significant role of hip muscle strength in the control of frontal plane knee motion.
Modeling a Viscoelastic Gymnastics Landing Mat during Impact
Authors: Mills Chris , Pain Matthew T.G. , Yeadon Maurice R.
Published: August 2016

Landing mats that can undergo a large amount of area deformation are now essential for the safe completion of landings in gymnastics. The objective of this study was to develop an analytical model of a landing mat that reproduces the key characteristics of the mat-ground force during impact with minimal simulation run time. A force plate and two high-speed video cameras were used to record the mat deformation during vertical drop testing of a 24-kg impactor. Four increasingly complex point mass spring-damper models, from a single mass spring-damper system, Model 1, to a 3-layer mass spring-damper system, Model 4, were constructed using Matlab to model the mat's behavior during impact. A fifth model composed of a 3-layer mass spring-damper system was developed using visual Nastran 4D. The results showed that Models 4 and 5 were able to match the loading phase of the impact with simulation times of less than 1 second for Model 4 and 28 seconds for Model 5. Both Models 4 and 5 successfully reproduced the key force-time characteristics of the mat-ground interface, such as peak forces, time of peak forces, interpeak minima and initial rates of loading, and could be incorporated into a gymnast-mat model.
Parameter Determination for a Computer Simulation Model of a Diver and a Springboard
Authors: Yeadon Maurice R. , Kong Pui W. , King Mark A.
Published: August 2016

This study used kinematic data on springboard diving performances to estimate viscoelastic parameters of a planar model of a springboard and diver with wobbling masses in the trunk, thigh, and calf segments and spring dampers acting at the heel, ball, and toe of the foot segment. A subject-specific angle-driven eight-segment model was used with an optimization algorithm to determine viscoelastic parameter values by matching simulations to four diving performances. Using the parameters determined from the matching of a single dive in a simulation of another dive resulted in up to 31% difference between simulation and performance, indicating the danger of using too small a set of kinematic data. However, using four dives in a combined matching process to obtain a common set of parameters resulted in a mean difference of 8.6%. Because these four dives included very different rotational requirements, it is anticipated that the combined parameter set can be used with other dives from these two groups.
The Interday Reliability of Leg and Ankle Musculotendinous Stiffness Measures
Authors: McLachlan Ken A. , Murphy Aron J. , Watsford Mark L. , Rees Sven
Published: August 2016

Two popular methods of assessing lower body musculotendinous stiffness include the hopping and oscillation tests. The disparity and paucity of reliability data prompted this investigation into leg musculotendinous stiffness (Kleg) and ankle musculotendinous stiffness (Kank) measures. Kleg and Kank were assessed on three separate occasions in 20 female subjects. Kleg was determined using bilateral hopping procedures conducted at 2.2 Hz and 3.2 Hz frequencies. Kank was assessed by perturbation of the subject's ankle musculotendinous unit on an instrumented calf raise apparatus at 70% of maximum isometric force (MIF). Excellent reliability was produced for all Kleg measures between all days, whereas Kank exhibited acceptable reliability after one session of familiarization. No relationship was evident between Kleg and Kank. It was concluded that no familiarization session was required for Kleg at the test frequencies and conditions tested, whereas at least one familiarization session was needed to ensure the reliable assessment of Kank.
Analysis of Center-of-Pressure Data during Unipedal and Bipedal Standing Using Fractional Brownian Motion Modeling
Authors: Burdet Cyril , Rougier Patrice
Published: August 2016

To question the relation between uni- and bipedal postural skills, 21 subjects were required to stand on a force platform through uni- and bipedal conditions. These two protocols are commonly used paradigms to assess the balance capacities of healthy and disabled patients. The recorded displacements of the center of pressure (CP) were decomposed along mediolateral and anteroposterior axes and assessed through variance positions and parameters obtained from fractional Brownian motion (fBm) modeling to determine the nature and the spatiotemporal organization of the successive controlling mechanisms. The variances underline the relative independence of the two tasks. Nevertheless, as highlighted by the fBm framework, postural correction is initiated for the unipedal stance after shorter time delays and longer covered distances. When compared to bipedal standing, one of the main characteristics of unipedal standing is to induce better-controlled CP trajectories, as deduced from the scaling regimes computed from the fBm modeling. Lastly, the control of the CP trajectories during the shortest time intervals along the anteroposterior axis appears identical for both uni- and bipedal conditions. Unipedal and bipedal standing controls should thus be viewed as two complementary tasks, each providing specific and complementary insights into the postural control organization.
Position Sense in the Lumbar Spine with Torso Flexion and Loading
Authors: Gade Venkata K. , Wilson Sara E.
Published: August 2016

Proprioception plays an important role in appropriate sensation of spine position, movement, and stability. Previous research has demonstrated that position sense error in the lumbar spine is increased in flexed postures. This study investigated the change in position sense as a function of altered trunk flexion and moment loading independently. Reposition sense of lumbar angle in 17 subjects was assessed. Subjects were trained to assume specified lumbar angles using visual feedback. The ability of the subjects to reproduce this curvature without feedback was then assessed. This procedure was repeated for different torso flexion and moment loading conditions. These measurements demonstrated that position sense error increased significantly with the trunk flexion (40%,p< .05) but did not increase with moment load (p= .13). This increased error with flexion suggests a loss in the ability to appropriately sense and therefore control lumbar posture in flexed tasks. This loss in proprioceptive sense could lead to more variable lifting coordination and a loss in dynamic stability that could increase low back injury risk. This research suggests that it is advisable to avoid work in flexed postures.
Drag Characteristics of Competitive Swimming Children and Adults
Authors: Kjendlie Per-Ludvik , Stallman Robert Keig
Published: August 2016

The aims of this study were to compare drag in swimming children and adults, quantify technique using the technique drag index (TDI), and use the Froude number (Fr) to study whether children or adults reach hull speed at maximal velocity (vmax). Active and passive drag was measured by the perturbation method and a velocity decay method, respectively, including 9 children aged 11.7 ± 0.8 and 13 adults aged 21.4 ± 3.7. The children had significantly lower active (kAD) and passive drag factor (kPD) compared with the adults. TDI (kAD/kPD) could not detect any differences in swimming technique between the two groups, owing to the adults swimming maximally at a higher Fr, increasing the wave drag component, and masking the effect of better technique. The children were found not to reach hull speed at vmax, and their Fr were 0.37 ± 0.01 vs. the adults 0.42 ± 0.01, indicating adults’ larger wave-making component of resistance at vmax compared with children. Fr is proposed as an evaluation tool for competitive swimmers.
Directional Sensitivity of Velocity Sense in the Lumbar Spine
Authors: Soltys Joseph S. , Wilson Sara E.
Published: August 2016

Regulating spinal motion requires proprioceptive feedback. While studies have investigated the sensing of static lumbar postures, few have investigated sensing lumbar movement speed. In this study, proprioceptive contributions to lateral trunk motion were examined during paraspinal muscle vibration. Seventeen healthy subjects performed lateral trunk flexion movements while lying prone with pelvis fixed. A 44.5-Hz vibratory stimulus was applied to the paraspinal muscles at the L3 level. Subjects attempted to match target paces of 9.5, 13.5, and 17.5 deg/s with and without paraspinal muscle vibration. Vibration of the paraspinal musculature was found to result in slower overall lateral flexion. This effect was found to have a greater influence in the difference of directional velocities with vibration applied to the left musculature. These changes reflect the sensitivity of lumbar velocity sense to applied vibration leading to the perception of faster muscle lengthening and ultimately resulting in slower movement velocities. This suggests that muscle spindle organs modulate the ability to sense velocity of motion and are important in the control of dynamic motion of the spine.
Wrist Splint Effects on Muscle Activity and Force during a Handgrip Task
Authors: Di Domizio Jennifer , Mogk Jeremy P.M. , Keir Peter J.
Published: August 2016

Wrist splints are commonly prescribed to limit wrist motion and provide support at night and during inactive periods but are often used in the workplace. In theory, splinting the wrist should reduce wrist extensor muscle activity by stabilizing the joint and reducing the need for co-contraction to maintain posture. Ten healthy volunteers underwent a series of 24 10-s gripping trials with surface electromyography on 6 forearm muscles. Trials were randomized between splinted and nonsplinted conditions with three wrist postures (30° flexion, neutral, and 30° extension) and four grip efforts. Custom-made Plexiglas splints were taped to the dorsum of the hand and wrist. It was found that when simply holding the dynamometer, use of a splint led to a small (<1% MVE) but significant reduction in activity for all flexor muscles and extensor carpi radialis (all activity <4% maximum). At maximal grip, extensor muscle activity was significantly increased with the splints by 7.9–23.9% MVE. These data indicate that splinting at low-to-moderate grip forces may act to support the wrist against external loading, but appears counterproductive when exerting maximal forces. Wrist bracing should be limited to periods of no to light activity and avoided during tasks that require heavy efforts.
Validity of Four Gait Models to Estimate Walked Distance from Vertical COG Acceleration
Authors: López Antonio M. , Álvarez Diego , González Rafael C. , Álvarez Juan C.
Published: August 2016

Pedometers are basically step counters usually used to estimate the distance walked by a pedestrian. Although their precision to compute the number of steps is quite accurate (about 1%), their feasibility to estimate the walked distance is very poor, as they do not consider the intrinsic variability of human gait. Reported results show values of 10% of precision in optimal conditions, increasing to 50% when conditions differ. Electronic accelerometer-based pedometers base their functioning on a basic processing of the vertical acceleration of the waist. Recently, different approaches have been proposed to relate such signals to the step length. This can lead to an improvement of the performance of this kind of device for estimating the walked distance. In this article, we analyze four gait models applied to the vertical accelerations of the body’s center of gravity, three biomechanical and one empirical. We compare their precision and accuracy. Results support the superior performance of three of them over an ideal pedometer. We also analyze their feasibility to be implemented in pedometer-like devices.
Helmet and Shoulder Pad Removal in Football Players with Unstable Cervical Spine Injuries
Authors: Dahl Michael C. , Ananthakrishnan Dheera , Nicandri Gregg , Chapman Jens R. , Ching Randal P.
Published: August 2016

Football, one of the country’s most popular team sports, is associated with the largest overall number of sports-related, catastrophic, cervical spine injuries in the United States (Mueller, 2007). Patient handling can be hindered by the protective sports equipment worn by the athlete. Improper stabilization of these patients can exacerbate neurologic injury. Because of the lack of consensus on the best method for equipment removal, a study was performed comparing three techniques: full body levitation, upper torso tilt, and log roll. These techniques were performed on an intact and lesioned cervical spine cadaveric model simulating conditions in the emergency department. The levitation technique was found to produce motion in the anterior and right lateral directions. The tilt technique resulted in motions in the posterior left lateral directions, and the log roll technique generated motions in the right lateral direction and had the largest amount of increased instability when comparing the intact and lesioned specimen. These findings suggest that each method of equipment removal displays unique weaknesses that the practitioner should take into account, possibly on a patient-by-patient basis.
Knee Strength Capabilities and Slip Severity
Authors: Wyszomierski Sarah A. , Chambers April J. , Cham Rakié
Published: August 2016

Slips and falls are a serious public health concern in older populations. Reduced muscle strength is associated with increased age and fall incidence. Understanding the relationships between specific joint muscle strength characteristics and propensity to slip is important to identify biomechanical factors responsible for slip-initiated falls and to improve slip/fall prevention programs. Knee corrective moments generated during slipping assist in balance recovery. Therefore, the study goal was to investigate the relationship between knee flexion/extension strength and slip severity. Isometric knee flexion/extension peak torque and rate of torque development (RTD) of the slipping leg were measured in 29 young and 28 older healthy subjects. Motion data were collected for an unexpected slip during self-paced walking. Peak slip velocity (PSV) of the slipping heel served as a slip severity measure. Within-sex and age group regressions relating gait speed-controlled PSV to strength of the slipping leg revealed significant inverse PSV-knee extension peak torque and PSV-knee flexion/extension RTD relationships in young males only. Differences in PSV-strength relationships between sex and age groups may be caused by greater ranges of strength capabilities in young males. In conclusion, the ability to generate higher, more rapid knee flexion/extension muscle moments (greater peak torque/RTD) may assist in recovery from severe slips.
Muscular Coordination of the Lower Extremities of Oarsmen during Ergometer Rowing
Authors: Janshen Lars , Mattes Klaus , Tidow Günter
Published: August 2016

In sweep-oar rowers, asymmetrical force production of the legs is a known phenomenon. The purpose of this study was to investigate the muscular activity of the legs that may cause this asymmetry even when oarsmen perform a symmetrical endurance task. Seven male young elite oarsmen performed an all-out 2000-m test on a rowing ergometer. During stroke kinematics, myoelectric activity of six muscles of each leg and pressure distribution under both feet were measured. Data were collected over two 30-s time windows starting 1 and 5 min after the test started. No significant differences were observed between legs and time windows for the range of motion of the hip, knee, and ankle joint as well as for the onset/offset timing of muscles. However, in the drive phase, the knee and hip muscles of the leg on the oar side (inside leg) showed 20–45% (both p < .05) higher activation intensities compared with the leg opposite the oar (outside leg). Corresponding to this, 56–91% (both p < .05) higher mean pressure values under the ball of the inside foot compared with the outside foot indicated an asymmetrical force production of the legs even under kinematically symmetrical working conditions.
Influence of Shock Waves and Muscle Activity at Initial Contact on Walk–Run Transition Evaluated by Two Models
Authors: Shung Kin , de Oliveira Carlos G. , Nadal Jurandir
Published: August 2016

The walk–run transition (WRT) is a well-described phenomenon without any known cause; however, mechanical variables related to human gait have been associated with the WRT. This study tested the hypothesis that shock waves in the tibia and 3rd lumbar vertebra in addition to activity of tibialis anterior, vastus lateralis, and erector spinae muscles could be responsible for the WRT. Thirty subjects walked and ran on a treadmill at 80%, 90%, 100%, 110%, and 120% of preferred transition speed. Shock waves were measured with skin-mounted accelerometers and muscle activity by surface electromyography. The influence on the WRT was analyzed with two models. The shock waves and muscle activity tended to a significant increase (p< .05) for both walking and running with increased speed. The only factor that appeared to be involved in the WRT mechanism was the activity of the tibialis anterior; however, this was only confirmed by one of the two models. The use of different models to analyze the same data for the WRT triggers may give different results; thus, a standard model is required to investigate the influence of given factors on biological phenomena.
Interactive Effects of Mass Proportions and Coupling Properties on External Loading in Simulated Forefoot Impact Landings
Authors: Gittoes Marianne J. R. , Kerwin David G.
Published: August 2016

This study aimed to gain insight into the individual and interactive effects of segmental mass proportions and coupling properties on external loading in simulated forefoot landings. An evaluated four-segment wobbling mass model replicated forefoot drop landings (height: 0.46 m) performed by two subjects. A comparison of the peak impact forces (GFzmax) produced during the evaluated landing and further simulated landings performed using modified (±5% perturbation) mass proportions and coupling properties was made. Independent segmental mass proportion changes, particularly in the upper body, produced a prominent change in GFzmax of up to 0.32 bodyweight (BW) whereas independent mass coupling stiffness and damping alterations had less effect on GFzmax (change in GFzmax of up to 0.18 BW). When combining rigid mass proportion reductions with damping modifications, an additional GFzmax attenuation of up to 0.13 BW was produced. An individual may be predisposed to high loading and traumatic and overuse injury during forefoot landings owing to their inherent inertia profile. Subject-specific neuromuscular modifications to mass coupling properties may not be beneficial in overriding the increased forces associated with larger rigid mass proportions.
Limitations of Functionally Determined Joint Centers for the Analysis of Athletic Human Movement: A Case Study of the Upper Limb
Authors: Roosen Andy , Pain Matthew T.G. , Begon Mickaël
Published: August 2016

Much research is ongoing into improving the accuracy of functional algorithms to determine joint centers (JC), but there has been limited testing using human movement data. This paper is in three parts: Part 1, errors in determining JCs from real human movement data using the SCoRE method; Part 2, variability of marker combinations during a punch; Part 3, variability in the JC due to reconstruction. Results indicate determining the JC of the shoulder or elbow with a triad of markers per segment with an accuracy greater than 20 mm is unlikely. Part 2 suggests conducting a pilot study with abundant markers to obtain triads, which are most stable due to differences of 300–400% in variability between triads. Variability due to the choice of reference frame for reconstruction during the punch ranged from 2.5 to 13.8 mm for the shoulder and 1.5 to 21.1 mm for the elbow. It would appear more pertinent to enhance the practical methods in situ than to further improve theoretical accuracy of functional methods.
Relationships between the Front Crawl Stroke Parameters of Competitive Unilateral Arm Amputee Swimmers, with Selected Anthropometric Characteristics
Authors: Osborough Conor D. , Payton Carl J. , Daly Daniel J.
Published: August 2016

The purpose of this study was to determine the relationships between swimming speed (SS), stroke length (SL), and stroke frequency (SF) for competitive single-arm amputee front crawl swimmers and assess their relationships with anthropometric characteristics. Thirteen highly trained swimmers (3 male, 10 female) were filmed underwater from a lateral view during seven increasingly faster 25-m front crawl trials. Increases in SS (above 75% of maximum SS) were achieved by a 5% increase in SF, which coincided with a 2% decrease in SL. At SSmax, interswimmer correlations showed that SF was significantly related to SS (r = .72; p < .01) whereas SL was not. Moderate but nonsignificant correlations suggested that faster swimmers did not necessarily use longer and slower strokes to swim at a common submaximal speed when compared with their slower counterparts. No correlations existed between SL and any anthropometric characteristics. Biacromial breadth, shoulder girth, and upper-arm length all significantly correlated with the SF used at SSmax. These findings imply that as a consequence of being deprived of an important propelling limb, at fast swimming speeds SF is more important than SL in influencing the performance outcome of these single-arm amputee swimmers.
Day-to-Day Consistency of Lower Extremity Kinematics during Walking and Running
Authors: Wolf Peter , List Renate , Ukelo Thomas , Maiwald Christian , Stacoff Alex
Published: August 2016

Before conclusions can be drawn with respect to the quality of adaptations in human gait, the day-to-day consistency of the variables of interest must be known. The present study estimated the day-to-day consistency of kinematic variables collected during barefoot walking and running. Sixteen healthy subjects performed two gait analysis sessions based on skin markers. Test sessions were at least 1 week apart. In total, 48 ranges of motion were monitored for the hip, knee, ankle, and midfoot joint. Based on differences between the repeated gait analysis sessions, the day-to-day consistency was estimated. It was found that the day-to-day consistency was of the magnitude of 3 to 4 degrees for almost all ranges of motion independently of the test condition, the investigated joints, or the cardinal body plane. It was concluded that future studies on effects of interventions or on the characterization of pathological versus normative gait should consider the provided values of day-to-day consistency to improve their interpretation and conclusions.
Variability in Lateral Positioning of Surface EMG Electrodes
Authors: Finni Taija , Cheng Sulin
Published: August 2016

The positions of EMG electrodes over the knee extensor muscles were examined in 19 healthy men using MR images; electrodes were placed according to the SENIAM (surface electromyography for non-invasive assessment of muscles) guidelines. From axial images, the medial and lateral borders of the muscles were identified, and the arc length of the muscle surface was measured. The electrode location was expressed as a percentage value from the muscle’s medial border. EMGs were recorded during isometric maximal contraction, squat jumps, and countermovement jumps and analyzed for cross-correlation. The results showed that variations in lateral positioning were greatest in vastus medialis (47% SD 11) and rectus femoris (68% SD 15). In vastus lateralis, the electrode was usually placed close to the rectus femoris (19% SD 6). The peak cross-correlation coefficient varied between 0.15 and 0.68, but was not associated with electrode location. It is recommended that careful consideration is given to the medial-lateral positioning of the vastus lateralis electrodes especially, so that the electrodes are positioned over the mid-muscle rather than in close proximity to rectus femoris.
Mathematical Functions and Their Properties as Relevant to the Biomechanical Modeling of Cell and Tissue Damage
Authors: Gefen Amit
Published: August 2016

The extrapolation of biological damage from a biomechanical model requires that a closed-form mathematical damage threshold function (DTF) be included in the model. A DTF typically includes a generic load variable, being the critical load (e.g., pressure, strain, temperature) causing irreversible tissue or cell damage, and a generic time variable, which represents the exposure to the load (e.g., duration, strain rate). Despite the central role that DTFs play in biomechanical studies, there is no coherent literature on how to formulate a DTF, excluding the field of heat-induced damage studies. This technical note describes six mathematical function types (Richards, Boltzmann, Morgan-Mercer-Flodin, Gompertz, Weibull, Bertalanffy) that are suitable for formulating a wide range of DTFs. These functions were adapted from the theory of restricted growth, and were fitted herein to describe biomechanical damage phenomena. Relevant properties of each adapted function type were extracted to allow efficient fitting of its parameters to empirical biomechanical data, and some practical examples are provided.
A Biomechanical Analysis of Handcycling: A Case Study
Authors: Faupin Arnaud , Gorce Philippe , Watelain Eric , Meyer Christophe , Thevenon Andre
Published: August 2016

The aim of this study was to investigate muscle activity, kinematic, and handgrip-force pattern generation during handcycling. One able-bodied participant performed a 1-min exercise test on a handcycle at 70 revolutions per minute. This article proposes an original data collection and analysis methodology that gathers synchronized kinematics, kinetics, and electromyography. Such data, which most often appear complex, are easily summarized using this methodology. This preliminary study has an new setup and offers good indications on the biomechanical pattern for handcycling movement analysis.
A Marker-Based Mean Finite Helical Axis Model to Determine Elbow Rotation Axes and Kinematics in Vivo
Authors: Chin Aaron , Lloyd David , Alderson Jacqueline , Elliott Bruce , Mills Peter
Published: August 2016

The predominance of upper-limb elbow models have been based on earlier lower-limb motion analysis models. We developed and validated a functionally based 2 degree-of-freedom upper-limb model to measure rotations of the forearm using a marker-based approach. Data were collected from humans and a mechanical arm with known axes and ranges of angular motion in 3 planes. This upper-limb model was compared with an anatomically based model following the proposed ISB standardization. Location of the axes of rotation relative to each other was determined in vivo. Data indicated that the functional model was not influenced by cross-talk from adduction-abduction, accurately measuring flexion-extension and pronation-supination. The functional flexion-extension axis in vivo is angled at 6.6° to the anatomical line defined from the humeral medial to lateral epicondyles. The pronation-supination axis intersected the anatomically defined flexion-extension axis at 88.1°. Influence of cross-talk on flexion-extension kinematics in the anatomical model was indicated by strong correlation between flexion-extension and adduction-abduction angles for tasks performed by the subjects. The proposed functional model eliminated cross-talk by sharing a common flexion axis between the humerus and forearm. In doing so, errors due to misalignment of axes are minimized providing greater accuracy in kinematic data.
Determination of the Drag Coefficient during the First and Second Gliding Positions of the Breaststroke Underwater Stroke
Authors: Vilas-Boas J. Paulo , Costa Lígia , Fernandes Ricardo J. , Ribeiro João , Figueiredo Pedro , Marinho Daniel , Silva António J. , Rouboa Abel , Machado Leandro
Published: August 2016

The purpose of the current study was to assess and to compare the hydrodynamics of the first and second gliding positions of the breaststroke underwater stroke used after starts and turns, considering drag force (D), drag coefficient (CD) and cross-sectional area (S). Twelve national-level swimmers were tested (6 males and 6 females, respectively 18.2 ± 4.0 and 17.3 ± 3.0 years old). Hydrodynamic parameters were assessed through inverse dynamics from the velocity to time curve characteristic of the underwater armstroke of the breaststroke technique. The results allow us to conclude that, for the same gliding velocities (1.37 ± 0.124 m/s), D and the swimmers’ S and CD values obtained for the first gliding position are significantly lower than the corresponding values obtained for the second gliding position of the breaststroke underwater stroke (31.67 ± 6.44 N vs. 46.25 ± 7.22 N; 740.42 ± 101.89 cm2 vs. 784.25 ± 99.62 cm2 and 0.458 ± 0.076 vs. 0.664 ± 0.234, respectively). These differences observed for the total sample were not evident for each one of the gender’s subgroups.
Treatment with Pharmacological Agents in Peripheral Arterial Disease Patients Does Not Result in Biomechanical Gait Changes
Authors: Huisinga Jessie M. , Pipinos Iraklis I. , Stergiou Nicholas , Johanning Jason M.
Published: August 2016

Pharmacological treatment has been used to alleviate the claudication symptoms and improve walking performance in peripheral arterial disease (PAD) patients. However, the effects of claudication treatments on gait mechanics have not been objectively indentified with biomechanical techniques. For this study, 20 PAD patients were assigned to take either pentoxifylline (n = 11) or cilostazol (n = 9), the two FDA-approved pharmacological therapies used to treat intermittent claudication symptoms. All patients completed a gait evaluation protocol that involved the acquisition of kinematic and kinetic gait data before use of the medication and after 12 weeks of treatment. Results showed that treatment with either pentoxifylline or cilostazol resulted in limited overall improvement in gait parameters including joint angles and joint moments. Walking speed was unchanged, in either treatment group, as a result of the medication. These results suggest that to improve biomechanical walking parameters of PAD patients, clinicians cannot rely on drug therapies alone.
Quantification of Patellofemoral Joint Reaction Forces during Functional Activities Using a Subject-Specific Three-Dimensional Model
Authors: Chen Yu-Jen , Scher Irving , Powers Christopher M.
Published: August 2016

The purpose of this study was to describe an imaging based, subject specific model that was developed to quantify patellofemoral joint reaction forces (PFJRF’s). The secondary purpose was to test the model in a group of healthy individuals while performing various functional tasks. Twenty healthy subjects (10 males, 10 females) were recruited. All participants underwent two phases of data collection: 1) magnetic resonance imaging of the knee, patellofemoral joint, and thigh, and 2) kinematic, kinetic and EMG analysis during walking, running, stair ascent, and stair descent. Using data obtained from MRI, a subject specific representation of the extensor mechanism was created. Individual gait data were used to drive the model (via an optimization routine) and three-dimensional vasti muscle forces and subsequent three-dimensional PFJRF’s were computed. The average peak PFJRF was found to be highest during running (58.2 N/kg-bwt), followed by stair ascent (33.9 N/kg-bwt), stair descent (27.9 N/kg-bwt), and walking (10.1 N/kg-bwt). No differences were found between males and females. For all conditions, the direction of the PFJRF was always in the posterior, superior, and lateral directions. The posterior component of the PFJRF always had the greatest magnitude, followed by superior and lateral components. Our results indicate that estimates of the magnitude and direction of the PFJRF during functional tasks can be obtained using a 3D-imaging based model.