bluuebunny/crossref_metadata_2025 huggingface dataset:
Determining the Force-Length-Velocity Relations of the Quadriceps Muscles: I. Anatomical and Geometric Parameters
Authors: Chow John W. , Darling Warren G. , Ehrhardt James C.
Published: August 2016

The purpose of this study was to determine the coordinates of the origin and insertion, muscle volumes, lengths, lines of action, and effective moment arm of the quadriceps muscles in vivo using magnetic resonance imaging (MRI) and radiography for a pilot study involving musculoskeletal modeling. Two magnetic resonance scans were performed, and axial images were obtained for the left thigh of a female subject in the anatomical position to measure muscle volume, coordinates of the origin and insertion, and muscle belly length at the anatomical position of each quadriceps muscle. Six knee radiographs were used to determine the effective moment arm of the quadriceps force at different knee flexion angles. A combination of MRI and radiography data was used to compute the muscle lengths at different knee flexion angles. The coordinates of the vastus lateralis, muscle volumes of individual quadriceps muscles, and effective moment arms were clearly different from the corresponding values from cadaver data reported in the literature. These comparisons demonstrate the advantages of using personalized muscle parameters instead of those collected from cadavers and dry-bone specimens.
The Effect of Patellar Taping on Quadriceps Activity Onset in the Absence of Pain
Authors: Parsons David , Gilleard Wendy
Published: August 2016

Patellofemoral taping is a technique used in the management of patellofemoral pain that has been shown to alter the pattern of muscle activation onset in symptomatic subjects. It is unknown, however, if this taping technique directly influences the patterns of muscle activity that controls patella position or if its benefits are more related to the effect of pain reduction. The purpose of this study was to investigate the effect of a taping technique on the muscle activation onset of selected quadriceps muscles where pain was not a confounding factor. Thirteen asymptomatic subjects completed a stair ascent and descent task with the right patella untaped and taped for a medial patella glide. Muscle activation onset was determined by computer algorithm from surface EMG of vastus lateralis (VL) and vastus medialis obliquus (VMO). Taping significantly delayed the muscle activation onset of VMO and VL during stair ascent. There was no significant change for stair descent. This effect may be an attempt by the motor control system to counter the mechanical effect of patella perturbation or may be due to cutaneous stimulation affecting threshold or recruitment of motor units.
Modeling the Stiffness Characteristics of the Human Body while Running with Various Stride Lengths
Authors: Derrick Timothy R. , Caldwell Graham E. , Hamill Joseph
Published: August 2016

A modified mass-spring-damper model was used to simulate the vertical ground reaction forces of a human runner as stride length was altered. Spring stiffness values were selected by an optimizing routine that altered model parameters to match the model ground reaction force curve to a runner’s actual ground reaction force curve. A mass in series with a spring was used to simulate the behavior of body structures that produce the active portion of the ground reaction force. A second mass in series with a spring-damper system was used to simulate the behavior of those components that cause the impact portion of the ground reaction force. The stiffness of the active spring showed a 51% decrease as subjects increased their stride length. The stiffness value of the impact spring showed a trend opposite that of the active spring, increasing by 20% as strides lengthened. It appears that the impact stiffness plays a role in preventing the support leg from collapsing in response to the increased contact velocities seen in the longer strides.
Effects of Hindlimb Suspension with Stretched or Shortened Muscle Length on Contractile Properties of Rat Soleus
Authors: Ohira Yoshinobu , Yoshinaga Tomoo , Yasui Wataru , Ohara Makoto , Tanaka Takato
Published: August 2016

The effects of chronic stretching or shortening of the soleus muscle of adult rats during hindlimb suspension on muscle mass and contractile properties were studied. Rats suspended with the ankle joint immobilized in either a dorsiflexed (Susp-DF. soleus stretched), a plantarflexed position (Susp-PF, soleus shortened), or without immobilization (Susp-Free. soleus shortened) were compared with cage control rats. Suspension-related muscle atrophy was prevented in Susp-DF. The relative muscle weight in Susp-PF was also less than in cage control and Susp-DF. Both isometric maximum twitch tension (Pt) and maximum tetanic tension (Po) in the Susp-Free and Susp-PF were less than control. Both Pt and Po in Susp-DF were normal. The twitch time-to-peak tension and one-half relaxation time tended to be reduced by chronic shortening of the muscle. The rate of tension development during a twitch (dp/dt), expressed as g/s, of Susp-Free group was decreased, but that expressed as g/s/g Pt was greater than controls. That in Susp-DF was subnormal. The fatigue resistance in Susp-Free was normal but was reduced in Susp-DF and Susp-PF. These data suggest that the decreases in the rat soleus mass and maximum tension production and the shift toward a fast-twitch type following hindlimb suspension are prevented by chronic stretching of muscle, although detrimental effect was induced for the fatigue resistance.
Floor Composition Affects Performance and Muscle Fatigue Following a Basketball Task
Authors: Streepey Jefferson W. , Gross M. Melissa , Martin Bernard J. , Sudarsan Sundravalli , Schiller Catherine M.
Published: August 2016

The relationship between playing surface and muscle fatigue was examined in 22 male subjects performing a simulated basketball task on a conventional wood floor and less stiff composite floor. Force and electromyographic activity (EMG) were measured during maximum and submaximum (10% of maximum) voluntary contractions of knee extensor and ankle plantarflexor muscles before and after completion of the simulated basketball task. Jump height was evaluated during the task, and perceived fatigue was assessed at the end of the task. Although not all subjects jumped significantly higher on the composite floor compared to the wood floor. competitive basketball players showed a significant improvement in jump height (3.4 cm. 6%) when jumping on the composite floor. Perceived fatigue was significantly lower for the composite floor (21.7%) than the wood floor (30.2%). The objective measures indicated the occurrence of fatigue; however, force and EMG magnitudes obtained during maximum exertions were not sensitive lo floor types. Post-task increase in EMG magnitude indicated a significant fatigue effect for the soleus muscle on the wood floor only. These findings suggest that the composite floor may benefit human performance without increasing fatigue during basketball-related activities.
The Speed-Accuracy Trade-Off in Human Gait Control When Running Towards Targets
Authors: Bradshaw Elizabeth J. , Sparrow W.A.
Published: August 2016

The study examined adjustments to gait when positioning the foot within a narrow target area at the end of an approach or “run-up” similar to the take-off board in long jumping. In one task, participants (n = 24) sprinted toward and placed their foot within targets of four different lengths for 8-m and 12-m approach distances while “running through” the target. In a second task, participants (n = 12) sprinted toward and stopped with both feet in the target area. Infra-red timing lights were placed along the approach strip to measure movement times, with a camera positioned to view the whole approach to measure the total number of steps, and a second camera placed to view the final stride, which was analyzed using an in-house digitizing system to calculate the final stride characteristics. In the run-through task, a speed-accuracy trade-off showing a linear relationship (r = 0.976, p < .05) between target length and approach time was found for the 8-m amplitude. An accelerative sub-movement and a later targeting or “homing-in” sub-movement were found in the approach kinematics for both amplitudes. Final stride duration increased, and final stride velocity decreased with a decrease in target length.
The Influence of Touchdown Parameters on the Performance of a High Jumper
Authors: Greig Matthew P. , Yeadon Maurice R.
Published: August 2016

In order to maximize the mass center vertical velocity at toe-off and thereby jump height the approach parameters in high jumping must be optimized. The present study aimed to determine the influence on jump height of the approach speed, the leg plant angle, and the knee angle at touchdown. Sixteen trials by an elite male high jumper were recorded in a single training session. Direct intervention was used to induce a change in technique so that a greater range in approach speed was obtained than was observed in competition. The optimum approach was shown to be fast (7.0 m · s–1) with the leg planted away from the vertical (34°) and with minimum knee flexion. A regression equation was obtained which was able to account for 79% of the observed variation in jump height. Jump height performance was shown to be most sensitive to changes in leg plant angle and knee angle at touchdown.
Factors Influencing the Performance of Springboard Dives of Increasing Difficulty
Authors: Miller Doris I. , Sprigings Eric J.
Published: August 2016

Major factors influencing the ability of divers to perform nontwisting springboard dives of increasing degree of difficulty were investigated. The analysis was based upon 49 dives (42 in pike and 7 in tuck) executed by male and female medalists in the 1996 Olympics. Videotapes were digitized to determine competitors’ vertical velocities and angular momenta at the beginning of dive flight. Centripetal force and resultant joint torque models were used to estimate the effort needed to perform multiple somersaulting dives. Increasing degree of difficulty by spinning in a pike rather than a tuck position for the same number of somersaults was associated with decreased vertical velocity at the start of dive flight, decreased angular velocity while somersaulting in a quasi-rigid position, and little change in centripetal force or related muscular effort. Increasing degree of difficulty by adding a somersault while rotating in a tuck rather than a pike position involved increases in vertical and angular velocities, a smaller increase in angular momentum, and notable increases in resultant joint torque and centripetal force. Sufficient muscular torque to maintain a compact spinning position was considered to be the major additional challenge facing divers making the transition from a 21/2 pike to a 31/2 tuck.
Differences in Batted Ball Speed with Wood and Aluminum Baseball Bats: A Batting Cage Study
Authors: Greenwald Richard M. , Penna Lori H. , Crisco Joseph J.
Published: August 2016

Differences in the performance of wood and metal baseball bats, measured as a function of batted ball speed, were quantified in a batting cage study. Two wood and five metal baseball bat models were studied with 19 players of various levels of experience ranging from high school to professional. Batted ball speeds from 538 hits were computed from high-speed 3-D ball position data collected with a commercially available system. In general, metal bats had significantly higher batted ball speeds than wood bats. Of the five metal bat models studied, one outperformed all other models and one bat was most similar to wood bats. The average difference in batted ball speed between wood bats and the highest performing metal bat was approximately 9 mph. Maximum batted ball speeds of 101 and 106 mph were measured for wood and metal bats, respectively. Increased skill level significantly increased the maximum batted ball speeds generated independent of bat model. Players of all experience levels were able to generate batted ball speeds in excess of 100 mph. While the results of this study are limited to the specific bats tested, this is the first study to measure and report differences in batted ball speeds among wood and metal bats.
Examining the Role of the Gastrocnemius during the Leg Curl Exercise
Authors: Gallucci Jason G. , Challis John H.
Published: August 2016

This study examined the moment-producing capabilities of the gastrocnemius during isokinetic knee flexion tasks. Nine healthy men were tested using a Biodex isokinetic dynamometer. Each one completed 3 maximum repetitions at 3 angular velocities, 30, 75, and 150º/s, with his ankle braced in either full dorsiflexion or full plantar flexion. A computer model was used to simulate the experimental tasks. Experimentally, the moment produced at the knee joint with the ankle dorsiflexed was significantly higher than the moment with the ankle plantar-flexed at all 3 angular velocities, p < 0.05. This suggests that lengthening the gastrocnemius allowed for greater contribution of the gastrocnemius to the total moment produced at the knee during isokinetic knee flexions. The simulations supported the experimental data and suggested that, with the ankle dorsiflexed, the gastrocnemius acts on a more favorable part of the muscle’s force-length curve compared with the plantar-flexed condition. The results of the experimental work, along with the simulations, demonstrated that lengthening the gastrocnemius significantly increased the moment produced at the knee joint during isokinetic knee flexion tasks. These results have implications for instructions given to persons who perform leg curls for muscle strengthening, and for the design of knee flexion exercise machines.
The Role of Footwear on Kinematics and Plantar Foot Pressure in Fencing
Authors: Geil Mark D.
Published: August 2016

The sport of fencing involves asymmetric motions, large forces, and rapid changes in momentum. Today’s fencing shoes are designed to facilitate footwork but they provide little plantar force dissipation. Plantar foot pressures and kinematics were measured in 13 fencers. The study compared fencing shoes to a standard court shoe. The court shoe resulted in a significant reduction in plantar pressures during the fencing lunge, advance-lunge, and fleche. However, most fencers preferred the fencing shoe for fencing. The court shoe tended to alter fencing kinematics, generally though not significantly decreasing the velocity of the front foot and the weapon hand, and increasing the range of motion and overall travel of the weapon hand. This effect on fencing mechanics may stem from the design of the court shoe, or from an accommodation effect.
Evaluation of a Torque-Driven Simulation Model of Tumbling
Authors: Yeadon Maurice R. , King Mark A.
Published: August 2016

The use of computer simulation models in studies of human movement is now widespread. Most of these models, however, have not been evaluated in a quantitative manner in order to establish the level of accuracy that may be expected. Without such an evaluation, little credence should be given to the published results and conclusions. This paper presents a simulation model of tumbling takeoffs which is evaluated by comparing the simulation output with an actual performance of an elite gymnast. A five-segment planar model was developed to simulate tumbling takeoffs. The model comprised rigid foot, leg, thigh, trunk + head, and arm segments with two damped linear springs to represent the elasticity of the tumbling track/ gymnast interface. Torque generators were included at the ankle, knee, hip, and shoulder joints in order to allow each joint to open actively during the takeoff. The model was customized to the elite gymnast by determining subject-specific inertia and torque parameters. Good agreement was found between actual and simulated tumbling performances of a double layout somersault with 1% difference in the linear and angular momenta at takeoff. Allowing the activation timings of the four torque generators to vary resulted in an optimized simulation that was some 0.32 m higher than the evaluation simulation. These simulations suggest the model is a realistic representation of the elite gymnast, since otherwise the model would either fail to reproduce the double layout somersault or would produce a very different optimized solution.
Upper Extremity Kinetics in Poultry Processing: A Comparison between Two Different Cutting Tasks
Authors: Waddell Dwight E. , Wyvill Craig , Gregor Robert J.
Published: August 2016

A field study was performed using a new data collection system looking at upper extremity kinetics during two different cutting tasks, wing vs. tender cuts, in three poultry plants. The Ergonomic Work Assessment System (EWAS) was designed to simultaneously record knife forces (Fx, Fy, and Fz), electromyographic (EMG) activity (forearm flexors/extensors), and goniometric data (wrist flexion/extension), all of which may represent risk factors associated with cumulative trauma disorders, specifically carpal tunnel syndrome (CTS). The objective of this study was to monitor workers in an unencumbered fashion as they performed two different poultry cutting tasks. It was assumed that the variables measured by EWAS would be able to discriminate between the two cuts and quantify possible differences between the two. The results confirmed that EWAS successfully showed significant differences in knife forces between the wing and tender cuts. Knife force differences were also observed between plants for the same cut. Differences in the two cuts were also identified in the EMG and wrist angles. EWAS successfully quantified variables that may represent risk factors associated with CTS in three poultry plants. Knowledge of a better quantitatively described external work environment may enable plants to better design rotation schedules for their deboners.
Dynamic Effects of Muscle Moment Arm Variation and Heavy External Loads on Hinge Joints
Authors: Biscarini Andrea
Published: August 2016

A two-dimensional model has been developed to predict and explain the effects of the variation of muscle moment arms during dynamic exercises involving heavy external loads. The analytical dependence of the muscle moment arm on the joint angle and on the origin and insertion position was derived for an ideal uniaxial hinge joint, modeling the muscle as a cable following an idealized minimum distance path from the origin to insertion that wraps around the bony geometry. Analytical expressions for the ratios of muscular force and the joint restraining reaction components to the external load weight were deduced, for isokinetic and static exercises, as a function of joint angle, joint angular velocity, and the other geometric parameters defining the model. Therefore, external load weight, joint angular velocity, and constraints to joint range of motion may be adjusted reciprocally in order to control in advance the peak value of the components of the joint load during isokinetic exercises. A dynamic formulation of forearm flexion/extension was solved numerically under the condition of constant biceps force in order to highlight the key role played by the variation in muscle moment arm in preventing injury during lifting of external loads against gravity. For example, our analysis indicates that the mean and peak resultant joint loads decrease by 5% and 14%, respectively, as a result of the change in muscle moment arm that occurs over the range of motion.
Impact Loading in Running Shoes with Cushioning Column Systems
Authors: Aguinaldo Arnel , Mahar Andrew
Published: August 2016

This study evaluated the effects of running shoes—with two types of cushioning column systems—on impact force patterns during running. Kinematic and ground reaction force data were collected from 10 normal participants wearing shoes with the following cushions: 4-column multicellular urethane elastomer (Shoe 1), 4-column thermoplastic polyester elastomer (Shoe 2), and 1-unit EVA foam (Shoe 3). Participants exhibited significantly lower impact force (p = .02) and loading rate (p = .005) with Shoe 2 (1.84 ± 0.24 BW; 45.6 ± 11.6 BW/s) compared to Shoe 1 (1.94 ± 0.18 BW; 57.9 ± 12.1 BW/s). Both cushioning column shoes showed impact force characteristics similar to those of a top-model running shoe (Shoe 3), and improved cushioning performance over shoes previously tested in similar conditions. Alterations in impact force patterns induced by lower limb alignment and running speed were negligible since participants did not differ in ankle position, knee position, or speed during all shod running trials. Ankle plantarflexion, however, was higher for barefoot running, indicating an apparent midfoot strike. Mechanical testing of each shoe during physiologic, cyclic loading demonstrated that Shoe 3 had the greatest stiffness, followed by Shoe 2 and Shoe 1. Shoe 1 was the least stiff of the two shoes with cushioning column systems, yet it displayed a significantly higher impact loading rate during running, possibly due to rearfoot motion alterations induced by the stiffer shoe. This study showed that even in similar shoe types, impact force and loading rate values could vary significantly with midsole cushion constructions. The findings of this study suggest that using these newer running shoes may be effective for runners who want optimal cushioning during running.
Combinations of Cycle Rate and Length for Minimizing the Muscle Power Requirement in Human Running
Authors: Yanai Toshimasa , Hay James G.
Published: August 2016

The purpose of this study was to test the hypothesis that, in human running at a given speed, runners select the combination of cycle rate (CR) and cycle length (CL) that minimizes the power generated by the muscles. A 2-D model of a runner consisting of a trunk and two legs was defined. A force actuator controlled the length of each leg, and a torque actuator controlled the amplitude and frequency of the backward and forward swing of each leg. The sum of the powers generated by the actuators was determined for a range of CRs at each of a series of speeds. The CR and CL vs. speed relationships selected for the model were derived from a series of CR and CL combinations that required the least power at each speed. Two constraints were imposed: the maximum amplitude of the forward and backward swing of the legs (±50°) and the minimum ground contact time needed to maintain steady-state running (0.12 sec). The CR vs. speed and CL vs. speed relationships derived on the basis of a minimum power strategy showed a pattern similar to those reported for longitudinal (within-subjects) analyses of human running. The anatomical constraint set a limit on the maximum CL attainable at a given speed, and the temporal constraint made CL decrease at high speeds. It was concluded that the process for selecting CL-CR combinations for human running has characteristics similar to the process for solving a constrained optimization problem.
Effects of Series Elasticity of the Muscle Tendon Complex on an Explosive Activity Performance with a Counter Movement
Authors: Nagano Akinori , Komura Taku , Fukashiro Senshi
Published: August 2016

The two goals of this study were (a) to evaluate the effects of the series elasticity of the muscle tendon complex on an explosive performance that allows a counter movement, and (b) to determine whether or not a counter movement is automatically generated in the optimal explosive activity, using computer simulation. A computer simulation model of the Hill-type muscle tendon complex, which is composed of a contractile element (CE) and a series elastic element (SEE), was constructed. The proximal end of the CE was affixed to a point in the gravitational field, and a massless supporting object was affixed to the distal end of the SEE. An inertia was held on the supporting object. The goal of the explosive activity was to maximize the height reached by the inertia. A variation of the SEE elasticity was examined within the natural range. The optimal pattern of neural activation input was sought through numerical optimization for each value of the SEE elasticity. Two major findings were obtained: (a) As the SEE elasticity increased, the maximal height reached by the inertia increased. This was primarily due to the enhanced force development of the CE. (b) A counter movement was automatically generated for all values of the SEE elasticity through the numerical optimization. It is suggested that it is beneficial to make a counter movement in order to reach a greater jump height, and the effect of making a counter movement increases as the elasticity of the muscle tendon complex increases.
Optimizing the Release Conditions for a Free Throw in Wheelchair Basketball
Authors: Schwark Brianne N. , Mackenzie Sasho J. , Sprigings Eric J.
Published: August 2016

The primary purpose of this study was to determine the optimal release conditions and corresponding arm movement pattern for the free throw for players classified as 3 to 4.5 on the international player classification system in wheelchair basketball. A 2-D, three-segment simulation model was used to investigate this problem. The computational process involved a two-step optimization scheme in which an outer computational loop was used to optimize the magnitude and timing of the muscle torques that generate the arm's motion, and an inner computational loop was used to determine the optimal angle and speed of the ball at the moment of release. The inner optimization loop revealed that Brancazio's (1981) and Hay's (1993) approaches to determining the optimal release angle produced identical results. The lowered seated height of the wheelchair basketball player required that the ball be released at a steeper angle with greater vertical velocity, and hence the need for greater shoulder torque. For the wheelchair player, the peak shoulder flexion torque generated by the model was reduced by approximately 43% when the upper arm was initially positioned at an angle approximately 40° below the horizontal, as compared to being positioned at an angle of 10° above the horizontal. For the wheelchair player, the optimal release angle and speed for a ball released at a horizontal distance of 4.09 m from the center of the basket, and 1.30 m below the rim, was computed to be 53.8° and 7.4 m/s, respectively.
Subject-Specific Estimates of Tendon Slack Length: A Numerical Method
Authors: Manal Kurt , Buchanan Thomas S.
Published: August 2016

Tendon develops force proportional to the distance it is stretched beyond its slack length. Tendon slack length is an important parameter for musculoskeletal models because it can greatly affect estimations of muscle force. Unfortunately, tendon slack length is a difficult parameter to measure, and therefore values for it are not often reported in the literature. In this paper we present a numerical method for estimating tendon slack length from architectural parameters of the muscle. Specifically, tendon slack length is computed iteratively from musculotendon lengths determined when a corresponding joint is held at two angles, and from knowledge of the muscle's optimal fiber length. Idealized data generated using SIMM were used to test the tendon slack length algorithm. The method converged to within 1% of the “true” tendon slack length specified in the SIMM model. The advantage of the method outlined in this paper is that it yields subject-specific estimates of tendon slack length, given subject-specific input parameters.
Measurement of Resistance Exercise Force Expression
Authors: Chiu Loren Z.F. , Schilling Brian K. , Fry Andrew C. , Weiss Lawrence W.
Published: August 2016

Displacement-based measurement systems are becoming increasingly popular for assessment of force expression variables during resistance exercise. Typically a linear position transducer (LPT) is attached to the barbell to measure displacement and a double differentiation technique is used to determine acceleration. Force is calculated as the product of mass and acceleration. Despite the apparent utility of these devices, validity data are scarce. To determine whether LPT can accurately estimate vertical ground reaction forces, two men and four women with moderate to extensive resistance training experience performed concentric-only (CJS) and rebound (RJS) jump squats, two sessions of each type in random order. CJS or RJS were performed with 30%, 50%, and 70% one-repetition maximum parallel back squat 5 minutes following a warm-up and again after a 10-min rest. Displacement was measured via LPT and acceleration was calculated using the finite-difference technique. Force was estimated from the weight of the lifter-barbell system and propulsion force from the lifter-barbell system. Vertical ground reaction force was directly measured with a single-component force platform. Two-way random average-measure intraclass correlations (ICC) were used to assess the reliability of obtained measures and compare the measurements obtained via each method. High reliability (ICC > 0.70) was found for all CJS variables across the load-spectrum. RJS variables also had high ICC except for time parameters for early force production. All variables were significantly (p < 0.01) related between LPT and force platform methods with no indication of systematic bias. The LPT appears to be a valid method of assessing force under these experimental conditions.
Influence of Laminotomies and Laminectomies on Cervical Spine Biomechanics under Combined Flexion-Extension
Authors: Ng Hong-Wan , Teo Ee-Chon , Zhang QingHang
Published: August 2016

Posterior decompressive techniques including one- and two-level laminotomies and laminectomies are often used in treating cervical stenosis. Previously, several in vitro studies were conducted to help us understand the biomechanical changes occurring in the cervical spine after these surgical techniques. However, changes in the intersegmental flexibility under combined flexion-extension remain unclear. In this study, a 3-D nonlinear intact model of the C2–C7 was developed to evaluate the influence of one- and two-level laminotomies and laminectomies on the intersegmental moment rotational responses and internal stresses. The intact model was validated by comparing the predicted responses against experimental data. The validated model was then modified to simulate various surgical techniques for finite element analysis. Results showed that one- and two-level laminectomies increase the C2–C7 rotation motions by about 15% and 20%, respectively. The predicted increase in rotational motions also correlated well with the published data. Furthermore, results indicated that laminectomies would influence the biomechanical responses on both the affected and adjacent motion segments. In contrast, laminotomies have no significant effects on cervical biomechanics. To conduct a one-level laminectomy study, current findings indicate that it takes at least five motion segments to capture the immediate postsurgical biomechanical changes accurately and realistically. Minimally invasive cervical spine surgeries with one- or two-level laminotomies are preferred over one- and two-level laminectomies. Also, there is no consideration as to the efficacy of the two techniques in decompressing the spinal cord or nerve roots, which is the goal of the surgery, but is not examined in this study.
Lower-Extremity Kinetic Response to Weighted-Vest Resistance during Stepping Exercise in Older Adults
Authors: Salem George J. , Flanagan Sean P. , Wang Man-Ying , Song Joo-Eun , Azen Stanley P. , Greendale Gail A.
Published: August 2016

Stepping activities when wearing a weighted vest may enhance physical function in older persons. Using 3 weighted-vest resistance dosages, this study characterized the lower-extremity joint biomechanics associated with stepping activities in elders. Twenty healthy community-dwelling older adults, ages 74.5 ± 4.5 yrs, performed 3 trials of forward step-up and lateral step-up exercises while wearing a weighted vest which added 0% body weight (BW), 5% BW, or 10% BW. They performed these activities on a force platform while instrumented for biomechanical analysis. Repeated-measures ANOVA was used to evaluate the differences in ankle, knee, and hip maximum joint angles, peak net joint moments, joint powers, and impulses among both steping activities and the 3 loading conditions. Findings indicated that the 5% BW vest increased the kinetic output associated with the exercise activities atall threelower-extremity joints. These increases ranged from 5.9% for peak hip power to 12.5% for knee extensor impulse. The application of an additional 5% BW resistance did not affect peak joint moments or powers, but it did increase the joint impulses by 4–11%. Comparisons between exercise activities, across the 3 loading conditions, indicated that forward stepping preferentially targeted the hip extensors while lateral stepping targeted the plantar flexors; both activities equally targeted the knee extensors. Weighted-vest loads of 5% and 10% BW substantially increased the mechanical demand on the knee extensors, hip extensors (forward stepping), and ankle plantar flexors (lateral stepping).
Comparison of Elasticity of Human Tendon and Aponeurosis in Knee Extensors and Ankle Plantar Flexors in Vivo
Authors: Kubo Keitaro , Kanehisa Hiroaki , Fukunaga Tetsuo
Published: August 2016

The purposes of this study were to compare the elasticity of tendon and aponeurosis in human knee extensors and ankle plantar flexors in vivo and to examine whether the maximal strain of tendon was correlated to that of aponeurosis. The elongation of tendon and aponeurosis during isometric knee extension (n= 23) and ankle plantar flexion (n= 22), respectively, were determined using a real-time ultrasonic apparatus, while the participants performed ramp isometric contractions up to voluntary maximum. To calculate the strain values from the measured elongation, we measured the respective length of tendon and aponeurosis. For the knee extensors, the maximal strain of aponeurosis (12.1 ± 2.8%) was significantly greater than that of the patella tendon (8.3 ± 2.4%),p< 0.001. On the contrary, the maximal strain of Achilles tendon (5.9 ± 1.4%) was significantly greater than that of aponeurosis in ankle plantar flexors (2.7 ± 1.4%),p< 0.001. Furthermore, for both knee extensors and ankle plantar flexors there was no significant correlation between maximal strain of tendon and aponeurosis. These results would be important for understanding the different roles of tendon and aponeurosis during human movements and for more accurate muscle modeling.
Potential Method of Optimizing the Klapskate Hinge Position in Speed Skating
Authors: Van Horne Scott , Stefanyshyn Darren J.
Published: August 2016

Acceptance of the klap speed skate was fully realized on the world speed skating scene in 1997. However, one of the most important unknowns regarding the klapskate was the positioning of the point of foot rotation (pivot point), which is believed to play an important role in optimizing klapskate performance. The purposes of this study were to explore the ankle, knee, and hip joint mechanical changes that occurred when the pivot point location was modified, and to determine whether maximal ankle torques provide predictive ability as to where the optimal pivot point positioning is for a skater. We tested 16 proficient skaters at three pivot point (PP) locations, ranging from just in front of the metatarsal-phalangeal joint to just in front of the first phalangeal joint. Of the 16 skaters, 10 were tested at a fourth position: tip of the toe. Push phase kinetics and kinematics were measured on a modified slide board. The optimal PP for each skater was defined as the position that allowed him to generate the most total push energy. Maximum voluntary static torque measures of the ankle and knee were collected on a Biodex dynamometer. Overall, anterior pivot point shifting led to a significant increase in ankle energy generated and a decrease in knee energy generated, with no significant change at the hip joint. We found no significant correlations between the static strength measures and the skaters' optimal pivot points.
Comparison of Three Heel Cord Surgeries in Children with Cerebral Palsy
Authors: Engsberg Jack R. , Oeffinger Donna J. , Ross Sandy A. , White Hank D. , Tylkowski Chester M. , Schoenecker Perry L.
Published: August 2016

This nonrandomized prospective descriptive study compared outcomes of three isolated heel cord surgeries in children with spastic diplegia cerebral palsy (CP): (1) heel cord advancement (HCA), (2) heel cord lengthening according to Vulpius (HCL-V), and (3) heel cord lengthening according to White (HCL-W). Thirty-two children were tested prior to and approximately 1 year after undergoing one of the three surgeries. Objective measures were collected for ankle passive and active range of motion, gross motor function measure (GMFM), and gait. All surgeries indicated significant improvements in end range passive and active ankle dorsifiexion, GMFM, and dorsifiexion during gait. Gait speed was significantly improved for the HCA group, but appeared to be the result of maturity. Gait speed for the HCL-V and HCL-W groups was unchanged. The study was the first to directly compare three heel-cord-lengthening surgeries.
Physical and Mechanical Properties of Various Field Lacrosse Balls
Authors: Crisco Joseph J. , Drewniak Elizabeth I. , Alvarez Martin P. , Spenciner David B.
Published: August 2016

Although the sport of lacrosse has evolved dramatically over the last few decades and is presently the fastest growing team sport in the United States, the current specifications for balls date back to 1943. The purpose of this study was to see if various commercially available field lacrosse balls meet these specifications and to determine additional mechanical properties of the ball that may more completely characterize ball performance. Eight models from several manufacturers were tested. Seven models were designated for game play, while one model was promoted as a practice ball. In accordance with the specifications, the mass, circumference, and rebound height were recorded for one dozen balls from each model. The load required to compress the balls 0.0125 m and the coefficient of restitution (COR) with an incident speed of 26.80 m/s were also determined. We found that some balls met several of the specifications, but none of the models had every ball meet all the specif cations. For the two measures of ball liveliness, rebound height had a weak correlation with COR. Ball compression loads averaged about 750 N over most models, but were almost 85% less for the practice model. It appears that current governing body specifications are outdated, as no ball model we tested met these specifications. The determination of ball liveliness at more realistic speeds should also be taken into account. Since balls with low compression loads can pass through face protectors worn by lacrosse players, the sport's governing bodies may wish to consider a specification on ball compression.
High School and College Baseball Pitchers' Response and Glove Movements to Line Drives
Authors: Young Douglas E. , Trachtman Doris , Scher Irving S. , Schmidt Richard A.
Published: August 2016

The timing of glove movements used by baseball pitchers to catch fast approaching balls (i.e., line drives) was examined in two tests to determine the responses and temporal characteristics of glove movements in high school and college baseball pitchers. Balls were projected toward the head of participants at 34.8 m·s–1 (78 mph) on average in an indoor test and at speeds approaching 58.1 m·s–1 (130 mph) in a field test. Pitchers caught over 80% and 15% of the projected balls in the indoor and field tests, respectively. Analyses of glove responses indicated that all pitchers could track the line drives and produce coordinated glove movements, which were initiated 160 ms (± 47.8), on average, after the ball was launched. College pitchers made initial glove movements sooner than high school pitchers in the field test (p = 0.012). In contrast, average glove velocity for pitchers increased from 1.33 (± 0.61) to 3.45 (± 0.86) m·s–1 across the tests, but did not differ between experience levels. Glove movement initiation and speed were unrelated, and pitchers utilized visual information throughout the ball's flight to catch balls that approached at speeds exceeding the estimated speeds in competitive situations.
Influence of Swimsuit Design and Fabric Surface Properties on the Butterfly Kinematics
Authors: Rogowski Isabelle , Monteil Karine , Legreneur Pierre , Lanteri Pierre
Published: August 2016

This study investigated the influence of the covering swimsuit and the fabric surface properties on the butterfly stroke kinematics. Surface properties were evaluated by wetting measurements of two fabric samples: one for training suits and one for competition suits. The surface of the second one was coated by mechanochemical treatment in order to modify its surface properties. Nine national level swimmers performed a 50-m butterfly at submaximal velocity in three swimsuit conditions: conventional, long, and coated long swimsuits. From video recording, the hip was digitized at the entry and exit of the swimmer's hand in order to calculate the duration, hip displacement, and hip linear velocity during underwater and recovery phases and during stroke. The results for wetting show that competition fabric was more water-repellent than training fabric, but both were isotropic. Moreover, the mechanochemical treatment increased water repellency and anisotropy. The swimming results indicated that, when compared to a conventional swimsuit, wearing a coated long swimsuit increased hip linear velocity during stroke, and particularly during the recovery phase which had a shorter duration. These results suggest that the covering swimsuit should be coupled with the water repellent and anisotropic properties of the fabric surface in order to improve swimming performance.
The Effect of Muscular Pre-Tensing on the Sprint Start
Authors: Gutiérrez-Dávila Marcos , Dapena Jesús , Campos José
Published: August 2016

Pre-tensed and conventional starts that exert, respectively, large and small forces against the starting blocks in the “set” position (0.186 vs. 0.113 N per newton of body weight) were analyzed. The starts were videotaped, and the horizontal forces exerted on feet and hands were obtained from separate force plates. In the pre-tensed start, the legs received larger forward impulses early in the acceleration (0.18 vs. 0.15 N·s per kilogram of mass in the first 0.05 s), but the hands received larger backward impulses (–0.08 vs. –0.04 N·s·kg–1). At the end of the acceleration phase, there was no significant difference in horizontal velocity between the two types of start and only trivial differences in the center of mass positions. The results did not show a clear performance change when the feet were pressed hard against the blocks while waiting for the gun.
Constitutive Modeling of Cartilaginous Tissues: A Review
Authors: Taylor Zeike A. , Miller Karol
Published: August 2016

An important and longstanding field of research in orthopedic biomechanics is the elucidation and mathematical modeling of the mechanical response of cartilaginous tissues. Traditional approaches have treated such tissues as continua and have described their mechanical response in terms of macroscopic models borrowed from solid mechanics. The most important of such models are the biphasic and single-phase viscoelastic models, and the many variations thereof. These models have reached a high level of maturity and have been successful in describing a wide range of phenomena. An alternative approach that has received considerable recent interest, both in orthopedic biomechanics and in other fields, is the description of mechanical response based on consideration of a tissue's structure—so-called microstructural modeling. Examples of microstructurally based approaches include fibril-reinforced biphasic models and homogenization approaches. A review of both macroscopic and microstructural constitutive models is given in the present work.
Effect of Fatigue on Single-Leg Hop Landing Biomechanics
Authors: Orishimo Karl F. , Kremenic Ian J.
Published: August 2016

The objective of this study was to measure adaptations in landing strategy during single-leg hops following thigh muscle fatigue. Kinetic, kinematic, and electromyographic data were recorded as thirteen healthy male subjects performed a single-leg hop in both the unfatigued and fatigued states. To sufficiently fatigue the thigh muscles, subjects performed at least two sets of 50 step-ups. Fatigue was assessed by measuring horizontal hopping ability following the protocol. Joint motion and loading, as well as muscle activation patterns, were compared between fatigued and unfatigued conditions. Fatigue significantly increased knee motion (p= 0.012) and shifted the ankle into a more dorsiflexed position (p= 0.029). Hip flexion was also reduced following fatigue (p= 0.042). Peak extension moment tended to decrease at the knee and increase at the ankle and hip (p= 0.014). Ankle plantar flexion moment at the time of peak total support moment increased from 0.8 (N⋅m)/kg (SD, 0.6 [N⋅m]/kg) to 1.5 (N⋅m)/kg (SD, 0.8 [N⋅m]/kg) (p= 0.006). Decreased knee moment and increased knee flexion during landings following fatigue indicated that the control of knee motion was compromised despite increased activation of the vastus medialis, vastus lateralis, and rectus femoris (p= 0.014,p= 0.014, andp= 0.017, respectively). Performance at the ankle increased to compensate for weakness in the knee musculature and to maintain lower extremity stability during landing. Investigating the biomechanical adaptations that occur in healthy subjects as a result of muscle fatigue may give insight into the compensatory mechanisms and loading patterns occurring in patients with knee pathology. Changes in single-leg hop landing performance could be used to demonstrate functional improvement in patients due to training or physical therapy.
The Correlation of Segment Accelerations and Impact Forces with Knee Angle in Jump Landing
Authors: Elvin Niell G. , Elvin Alex A. , Arnoczky Steven P. , Torry Michael R.
Published: August 2016

Impact forces and shock deceleration during jumping and running have been associated with various knee injury etiologies. This study investigates the influence of jump height and knee contact angle on peak ground reaction force and segment axial accelerations. Ground reaction force, segment axial acceleration, and knee angles were measured for 6 male subjects during vertical jumping. A simple spring-mass model is used to predict the landing stiffness at impact as a function of (1) jump height, (2) peak impact force, (3) peak tibial axial acceleration, (4) peak thigh axial acceleration, and (5) peak trunk axial acceleration. Using a nonlinear least square fit, a strong (r = 0.86) and significant (p ≤ 0.05) correlation was found between knee contact angle and stiffness calculated using the peak impact force and jump height. The same model also showed that the correlation was strong (r = 0.81) and significant (p ≤ 0.05) between knee contact angle and stiffness calculated from the peak trunk axial accelerations. The correlation was weaker for the peak thigh (r = 0.71) and tibial (r = 0.45) axial accelerations. Using the peak force but neglecting jump height in the model, produces significantly worse correlation (r = 0.58). It was concluded that knee contact angle significantly influences both peak ground reaction forces and segment accelerations. However, owing to the nonlinear relationship, peak forces and segment accelerations change more rapidly at smaller knee flexion angles (i.e., close to full extension) than at greater knee flexion angles.