bluuebunny/crossref_metadata_2025 huggingface dataset:
Three-Dimensional Analysis of the Men‘s 100-m Freestyle during the 1992 Olympic Games
Authors: Cappaert Jane M. , Pease David L. , Troup John P.
Published: August 2016

Twelve male 100-m freestyle swimmers were videotaped during the 1992 Olympic Games. Four cameras, two above water and two below, recorded the same stroke cycle of the swimmer at approximately the 40- to 45-m mark. The whole body and the recovering arms were digitized from the videotapes to recreate a complete stroke cycle. Body position variables and hand reaction forces (Schleihauf, 1979) were calculated. Swimmers were divided into elite and subelite groups based on their swimming velocity and were compared for differences in biomechanical variables. Elites used slightly lower hand forces while maintaining a higher propelling efficiency. Subelites had opposite rotations about the longitudinal axis of the body rather than symmetrical body roll. The elite swimmers were different from subelites in that their pulling patterns were more efficient and their body position was more streamlined. These variables assisted them in achieving faster swimming velocities without requiring higher propulsive forces.
Internal Loading of the Foot and Ankle during Impact in Running
Authors: Cole Gerald K. , Nigg Benno M. , Fick Gordon H. , Morlock Michael M.
Published: August 2016

A 3-D model was used in this study to determine the influence of midsole hardness, as well as the influence of running in shoes in comparison to barefoot, on the contact forces in the joints of the foot and ankle during running. The results showed that there were no statistical differences in the magnitude and rate of joint loading for changing midsole hardness, nor were there any general trends observed in the measured variables. However, both the magnitude and rate of loading in the subtalar and ankle joints during the impact phase were found to be greater in the barefoot condition than the shod condition. The results suggest that if running injuries are assumed to be related to the impact of heel-strike, running in shoes may aid in preventing injuries, whereas it is still questionable whether changes in the midsole hardness have a general influence on the incidence of impact-related injuries.
Modeling Human Body Motion with Application in Crash Victim Simulation
Authors: Huang Shyh-Chour
Published: August 2016

This paper presents a description of a general -purpose nonlinear model of the human body. The model is developed to simulate human response to high force and high acceleration as typically experienced in vehicle accidents. The model is composed of connected bodies of segments representing the torso and limbs of the human frame. Nonlinear springs and dampers are used at the connection joints to represent human anatomical characteristics and limits imposed by muscles, ligaments, and soft tissue. The governing dynamical equations are developed using Kane's equations (Kane <&: Levin-son, 1985) and multibody dynamics analysis procedures developed by Huston et al. (1974, 1975, 1978). These equations and procedures form the basis for the algorithms of a computer code. The equations are solved numerically using a fourth-order Runge-Kutta integrator. The results of several accident simulations are also presented.
The Optimal Placement of Boxes on the Shelves of a Food Product Warehouse
Authors: Smyth Gilmen , Gagnon Micheline
Published: August 2016

An experimental study was undertaken to optimize the placement of boxes on the shelves in a food product warehouse by minimizing joint loadings on the shoulders and on the lower back as criteria. A dynamic sagittal plane model was used to estimate net muscular moments on the shoulders, and a model of internal forces was used to estimate compression forces on the L5/ SI intervertebral disk. Lifting boxes of 6.4 kg or more produced compression forces at L5/S1 above the “action limit” of the National Institute for Occupational Safety and Health (NIOSH, 1981). Regression methods were then used to estimate joint loadings for each product at each working height and for each task. Optimizing the placement of products by minimizing loadings on the lower back reduced overall loadings by as much as 15% for certain racks. For minimizing loadings on the shoulders, results indicated that this variable Was not sensitive to different placements of boxes on the shelves.
Optimal Javelin Release
Authors: Best Russell J. , Bartlett Roger M. , Sawyer Richard A.
Published: August 2016

This paper reports a study of the optimal release of men's and women's new and old rule javelins involving modeling, simulation, optimization (including sensitivity analysis), and simulation evaluation. Because of the lack of repro-ducibility in earlier results of two-dimensional flight simulation research, the paper presents a continuation of the two-dimensional model used previously. As expected, each javelin was found to have a different optimal release for a given individual, and the optimal release varied with the thrower's nominal release speed. A limited degree of simulation evaluation was achieved by comparison of the model and simulation results with measured throws. Within the constraints of measurement error, this tended to support both the adequacy of the two-dimensional model and the results of the simulations for such high standard throws. However, further experimental studies to quantify the angle of yaw (sideslip) in measured wind conditions are recommended to assess any changes needed to the two-dimensional model of javelin throwing and to determine the advisability of including this three-dimensional aspect of javelin release in future simulations.
The Effect of Varying Midsole Hardness on impact Forces and Foot Motion during Foot Contact in Running
Authors: Wit Brigit De , Clercq Dirk De , Lenoir Matthieu
Published: August 2016

The purpose of this study was to investigate the influence of midsole hardness on both impact forces and rearfoot motion. Seven trained male long-distance runners were assessed with a Kistler force plate and with high-speed video, while running at 4.5 ± 0.1 m · s"1 with soft and hard shoe soles (EVA; soft shore Asker C40; hard shore Asker C65). The results showed smaller initial vertical impact peaks, occurring with a higher loading rate, and a significantly larger and faster initial eversion when subjects ran with hard shoes. Support is given to the concept that a more pronounced initial eversion offers an additional deceleration mechanism (Stacoff, Denoth, Kaelin, & Stuessi, 1988) also increasing the eccentric loading of the inverting muscles. On the other hand, during midstance soft shoe soles were found to produce a larger maximum eversion and pronation, also imposing an increased load on the same muscles. So, a good running shoe should be focused on a balance between reducing impact forces and reducing overpronation.
Estimated Patellofemoral Compressive Forces and Contact Pressures during Dance Landings
Authors: Simpson Kathy J. , Jameson Eugene G. , Odum Susan
Published: August 2016

Patellofemoral dysfunctions due to abnormal force loading are significant problems for dancers. Increased jump length was predicted to require increased quadriceps force during landing, which would increase patellofemoral forces and pressures. Six female dancers performed 10 traveling jumps each at 30, 60, and 90% maximum jump displacements (JDs). A sagittal view of the landing onto a force platform (500 Hz) was filmed (100 fps). Repeated-measures ANOVA (JD) and Scheffé post hoc analyses (p < .05) showed that greater peak patellofemoral pressures occurred at longer JDs and the corresponding times to these events decreased and knee flexion increased. Previous research and these findings indicate that different regions of the patella may endure higher loads at greater JDs even though the contact areas increase with greater patellofemoral forces. However, greater knee flexion and velocity could indicate more rapid distribution of load to various patellar regions, which would reduce the time any given patellofemoral region would be subjected to high loads.
Kinematics, Kinetics, and Muscle Activation during Explosive Upper Body Movements
Authors: Newton Robert U. , Kraemer William J. , Häkkinen Keijo , Humphries Brendan J. , Murphy Aron J.
Published: August 2016

The aim of this study was to investigate the kinematics, kinetics, and neural activation of the traditional bench press movement performed explosively and the explosive bench throw in which the barbell was projected from the hands. Seventeen male subjects completed three trials with a bar weight of 45% of the subject's previously determined 1RM. Performance was significantly higher during the throw movement compared to the press for average velocity, peak velocity, average force, average power, and peak power. Average muscle activity during the concentric phase for pectoralis major, anterior deltoid, triceps brachii, and biceps brachii was higher for the throw condition. It was concluded that performing traditional press movements rapidly with light loads does not create ideal loading conditions for the neuromuscular system with regard to explosive strength production, especially in the final stages of the movement, because ballistic weight loading conditions where the resistance was accelerated throughout the movement resulted in a greater velocity of movement, force output, and EMG activity.
Modeling Effects of Muscle Fatigue on Unilateral Postural Control
Authors: Davis Brian L. , Grabiner Mark D.
Published: August 2016

Measurement of postural sway is a valuable research and clinical tool that can provide information related to various central and peripheral elements of the nervous system. The present study involved modeling single-limb standing as an inverted pendulum tethered to a supporting surface by two sets of springs that simulated the stiffness of muscles spanning the joint and the inherent stiffness of the joint itself. There are four key elements of this model: (a) joint stiffness is greater in the frontal plane compared to the sagittal plane (neither being affected by fatigue), (b) muscle stiffness is exponentially related to its extension from a resting position, (c) muscle stiffness is reduced by fatigue, and (d) an "ankle strategy" is used to maintain upright single-limb posture. It is concluded that an inverted pendulum model can be used to adequately predict sway frequencies and amplitudes in the mediolateral (ML) and anteroposterior (AP) directions for single-limb stance pre- and postfatigue. In particular, it is possible for acute muscle fatigue to increase sway in the ML direction but not necessarily in the AP direction.
Postural Dynamics in Upright and Inverted Stances
Authors: Slobounov Semyon M. , Newell Karl M.
Published: August 2016

This study provides a comparative analysis of certain features of upright and inverted stance in collegiate-level competitive gymnastic and diving athletes. A particular focus was the compensatory movement strategies used to maintain inverted stance. The analyses revealed that the motion of the center of pressure was significantly greater in the hand stance as opposed to the upright stance condition. Instability increased over the duration of a 15-s hand stance trial, and it was paralleled by the introduction of a small set of compensatory movement strategies that included enhanced motion at the distal segments of the legs and at the elbow joint. The compensatory movement strategies appeared to be in support of minimizing variability of motion in the head and trunk. The relative contribution of the principal sources of this instability in the hand stance remains to be determined.
Kinesiological Factors in Vertical Jump Performance: Differences among Individuals
Authors: Aragón-Vargas Luis F. , Gross M. Melissa
Published: August 2016

The purpose of this study was to investigate the kinesiological factors that distinguish good jumpers from poor ones, in an attempt to understand the critical factors in vertical jump performance(VJP).Fifty-two normal, physically active male college students each performed five maximal vertical jumps with arms akimbo. Ground reaction forces and video data were collected during the jumps. Subjects' strength was tested isometrically. Thirty-five potential predictor variables were calculated for statistical modeling by multiple-regression analysis. At the whole-body level of analysis, the best models (which included peak and average mechanical power) accounted for 88% ofVJPvariation (p< .0005). At the segmental level, the best models accounted for 60% of variation inVJP(p< .0005). Unexpectedly, coordination variables were not related toVJP. These data suggested thatVJPwas most strongly associated with the mechanical power developed during jump execution.
Twisting Double Somersault High Bar Dismounts
Authors: Yeadon Maurice R.
Published: August 2016

At the 1988 Seoul Olympic Games, four double somersault dismounts with one twist and four double somersault dismounts with two twists were filmed using two 16 mm cameras during the men's horizontal bar competitions. Contributions to tilt angle reached at the midtwist position, determined using computer simulations based on modifications of the data obtained from film, were used as measures of the twisting potential of various techniques. The amount of tilt produced was greater when total twist was greater and when the body was tucked rather than straight. The twisting techniques used varied with the timing of the twist within the two somersaults. Contact contributions were larger when there was more twist in the first somersault. When there was little or no twist in the first somersault, the major contribution came from aerial techniques that comprised mainly arm movements and asymmetrical hip movements in the flight phase.
Does Elastic Energy Enhance Work and Efficiency in the Stretch-Shortening Cycle?
Authors: Schenau Gerrit Jan van Ingen , Bobbert Maarten F. , de Haan Arnold
Published: August 2016

This target article addresses the role of storage and reutilization of elastic energy in stretch-shortening cycles. It is argued that for discrete movements such as the vertical jump, elastic energy does not explain the work enhancement due to the prestretch. This enhancement seems to occur because the prestretch allows muscles to develop a high level of active state and force before starting to shorten. For cyclic movements in which stretch-shortening cycles occur repetitively, some authors have claimed that elastic energy enhances mechanical efficiency. In the current article it is demonstrated that this claim is often based on disputable concepts such as the efficiency of positive work or absolute work, and it is argued that elastic energy cannot affect mechanical efficiency simply because this energy is not related to the conversion of metabolic energy into mechanical energy. A comparison of work and efficiency measures obtained at different levels of organization reveals that there is in fact no decisive evidence to either support or reject the claim that the stretch-shortening cycle enhances muscle efficiency. These explorations lead to the conclusion that the body of knowledge about the mechanics and energetics of the stretch-shortening cycle is in fact quite lean. A major challenge is to bridge the gap between knowledge obtained at different levels of organization, with the ultimate purpose of understanding how the intrinsic properties of muscles manifest themselves underin-vivo-like conditions and how they are exploited in whole-body activities such as running. To achieve this purpose, a close cooperation is required between muscle physiologists and human movement scientists performing inverse and forward dynamic simulation studies of whole-body exercises.
The Isometric Knee Extension Moment-Angle Relationship: Experimental Data and Predictions Based on Cadaver Data
Authors: Meijer Kenneth , Bosch Peter , Bobbert Maarten F. , van Soest Arthur J. , Huijing Peter A.
Published: August 2016

The influence of parameter values (i.e., fiber optimum lengths and moment arms) and simplification of the geometry of a Hill-type muscle model on the prediction of normalized maximal isometric knee extension moment to knee joint angle relationship was studied. For that purpose, the geometry of m. quadriceps femoris was modeled in considerable detail, and all parameter values were determined on one set of cadaver specimens that had been selected for muscular appearance. The predicted relationship was compared to that measured in human subjects over the full range of physiological knee angles, and a good correspondence was found (r = .96). The good correspondence could be attributed to the substitution of realistic parameter values into the model. Incorporating complex muscle geometry into the model resulted in a small additional improvement of the prediction. It was speculated that the variation in results of cadaver measurements among studies reflects true differences caused by individuals' levels of physical activity in the period preceding death.
Quantitative Intramuscular Myoelectric Activity of Lumbar Portions of Psoas and the Abdominal Wall during Cycling
Authors: Juker Daniel , McGill Stuart , Kropf Peter
Published: August 2016

The purpose of this study was to quantify activation using intramuscular EMG from lumbar psoas and the three layers of the abdominal wall during several styles of cycling: normal posture (slightly flexed), upright posture, racing in flexed posture, standing up from the saddle, and standing during maximal sprint effort. Lumbar erector spinae and rectus femoris were also monitored with surface electrodes. Results demonstrated that the activity patterns were influenced by the style of cycling. Furthermore, psoas activity peaked at 14% of MVC (or less) during the upstroke phase of normal cycling but became much more active at TDC during flexed cycling (approximately 30% MVC) and approached 60% of MVC during sprinting. Generally, the abdominal wall was activated to relatively low but continual levels except during standing and sprinting. Erector spinae activity was very low at less than 5% MVC throughout the cycle until standing or sprinting styles were adopted. These normalized and scaled data on deep muscle activity during ergometer cycling provide insight into the functioning of these muscles; this information can be used to prescribe rehabilitation and training programs and can help biomechanists understand muscle activity associated with cycling.
Hydrodynamic Characteristics of a Swimmer’s Hand
Authors: Sanders Ross H.
Published: August 2016

The main purpose of this study was to develop a model for calculating forces produced by a swimmer’s hand, with the thumb adducted, accelerating in the direction of flow. The model included coefficients to account for the velocity and acceleration of the hand. These coefficients were designed to calculate forces in the direction opposite the motion (drag) and two components of lift orthogonal to the direction of motion. To determine the coefficients, three-dimensional forces acting on a resin cast of a swimmer’s hand were recorded while accelerating the hand from rest to 0.45 m · s−1 and 0.6 m · −1 in a towing tank. The hand orientation was varied throughout the entire range at 5° increments. Three-dimensional surfaces describing the magnitude of the coefficients as functions of pitch and sweepback angle were produced. It was found that acceleration coefficients as well as velocity coefficients are required for accurate modeling of the forces produced by the hand in swimming. The forces generated by the hand are greatest when pitch angles approach 90° due to the large contribution by the drag component. However, at pitch angles near 45° and sweepback angles near 45° and 135°, lift forces contribute substantially.
Maximum Trunk Flexion Angle during the Sit to Stand Is Not Determined by Knee or Trunk-Hip Extension Strength in Healthy Older Adults
Authors: Lundin Thomas M. , Jahnigen Dennis W. , Grabiner Mark D.
Published: August 2016

When rising from a chair, older adults have been reported to use a strategy in which the trunk is flexed to a greater extent than young adults, a strategy attributed by some to concerns with the postural stability demands of the task. This study determined the extent to which maximum trunk flexion angle during a self-paced sit-to-stand from a standardized initial position was influenced by the maximum isometric strength of the knee and trunk/hip extensor muscles in older adults. The hypothesis was that the larger maximum trunk flexion angle attained by older adults when rising from a chair is related to the maximum isometric strength of the knee and trunk-hip extensor muscles. To test this hypothesis, maximum voluntary isometric strength of the trunk extensor and knee extensor muscles of 28 older men and women were measured. Trunk motion during the sit-to-stand by these adults was men assessed using motion analysis. Multiple regression was used to characterize the relationship between the maximum trunk flexion angle and maximum isometric knee extensor and trunk extensor muscle strength. The derived relationship was neither statistically significant nor biomechanically meaningful. This result suggests that the trunk flexion angle attained by healthy older adults when rising from a chair from a standardized initial position is not influenced by knee extension and trunk-hip extension strength as measured in the present study.
Internal Rotation of the Upper-Arm Segment during a Stretch-Shorten Cycle Movement
Authors: Elliott Bruce C. , Baxter Kevin G. , Besier Thor F.
Published: August 2016

This research examined the influence on performance of no-pause and mean delays of 0.97 s and 1.5 s between the eccentric and concentric phases of the stretch-shorten cycle movement of internal rotation (IR) of me upper arm. Videography and surface electromyography were used in the assessment of 19 athletes throwing a baseball in a manner that constrained all degrees of freedom other than upper-arm IR. Results demonstrated that the pectoralis major, latissimus dorsi, and anterior deltoid muscles were all active at above 100% maximum voluntary contraction (MVC) during IR. The maximum velocity of the wrist decreased with increasing pause time between me eccentric and concentric phases of the IR movement. A mean 21.9% augmentation to the maximum wrist velocity was recorded when the no-pause delay and a mean delay of 1.5 s were compared. There were no electromyographically discernible differences recorded either prior to or after release for any of the monitored muscles during IR across the pause conditions. It is evident therefore that the benefits of a prestretch during external rotation (ER) have a significant influence on the subsequent velocity of IR.
Computational Methods Used in the Determination of Loading Rate: Experimental and Clinical Implications
Authors: Woodard C. Mark , James Margaret K. , Messier Stephen P.
Published: August 2016

Our purpose was to compare methods of calculating loading rate to the first peak vertical ground reaction force during walking and provide a rationale for the selection of a loading rate algorithm in the analysis of gait in clinical and research environments. Using vertical ground reaction force data collected from 15 older adults with symptomatic knee osteoarthritis and 15 healthy controls, we: (a) calculated loading rate as the first peak vertical force divided by the time from touchdown until the first peak; (b) calculated loading rate as the slope of the least squares regression line using vertical force and time as the dependent and independent variables, respectively; (c) calculated loading rate over discrete intervals using the Central Difference method; and (d) calculated loading rate using vertical force and lime data representing 20% and 90% of the first peak vertical force. The largest loading rate, which may be of greatest clinical importance, occurred when loading rates were calculated using the fewest number of data points. The Central Difference method appeared to maximize our ability to detect differences between healthy and pathologic cohorts. Finally, there was a strong correlation between methods, suggesting that all four methods are acceptable. However, if maximizing the chances of detecting differences between groups is of primary importance, the Central Difference method appears superior.
Measurement of Applied Force and Deflection in the Javelin Throw
Authors: Maeda Masato , Shamoto Eiji , Moriwaki Toshimichi , Nomura Haruo
Published: August 2016

The present paper presents a new sensor to measure 6 components of force and 2 components of deflection applied to the javelin during the throw. Since the javelin is deflected and vibraled during throwing, measurement of force and deflection applied to the javelin will provide important information for throwers in how to better throw the javelin and to design javelins with better dynamic characteristics. The sensor is designed not to significantly change the static and dynamic characteristics of the javelin. The force sensor performs well in terms of linearity and crosstalk, and the javelin equipped with this sensor has similar characteristics to ordinary javelins. The present paper also presents an example of measurement in the javelin throw.
Surface Responses of Maximum Isokinetic Ankle Torque Generation Capability
Authors: Khalaf Kinda A. , Parnianpour Mohamad , Karakostas Tasos
Published: August 2016

The majority of existing normative torque generation capability (torque capability for short) databases are reported in the form of torque as a function of joint angle. although it is well recognized that torque capability is a function of both the joint angular position and angular velocity. The main objective of this study was to develop the methodology of 3-D dynamic representation of torque capability using the ankle joint as an example. The ankle torque capability of 20 males and females was assessed at 5 levels of ankle joint angular positions and velocities in each direction of plantar and dorsi flexion. The ANOVA results indicated significant main effects of joint angular position, angular velocity, direction, and gender, in addition to the interaction effect of angular position and velocity (p < .003) on the torque capability of the ankle joint. The regression analysis indicated that an individualized quadratic surface response performed significantly belter than the models developed for each gender or the whole population using the coefficient of determination and standard error of the regression as criteria. Such 3-D representation of torque capability has a broad spectrum of applications ranging from rehabilitation and ergonomic to biomechanical applications.
Instrumentation to Quantify Exercise Using an Impulse Inertial System
Authors: Phillips Todd C. , Kohles Sean S. , Orwin John F. , Brody Lori Thein , McCabe Ronald P. , Vanderby Ray
Published: August 2016

An impulse-momentum exercise system was instrumented for collection of kinematic and kinetic data during shoulder exercise. The objective of this study was to quantify the dynamics of an exercise system that utilizes a weighted shuttle (22.2 N) traveling on a rail system and evaluate its efficacy as an exercise and rehabilitative tool. Two healthy adults (mean age. 30.0 years) were tested utilizing 2 protocols. The first protocol required the subject to maintain tension in the system while externally rotating the upper arm from neutral to 90° relative to the shoulder and then internally rotating back to the initial position. In me second protocol, the range of motion was similar, but each subject was instructed to carry out the exercise as rapidly as possible without regard to the tension in the rope, thus creating an impulsive load. Average peak loads up to 87.9 and 137.0 N were recorded using the first and second protocols. respectively. Average maximum loads using the second protocol were approximately 50 N greater than those using the first protocol (p < .05). Representative calculations demonstrated that less mechanical work was performed during the first protocol (−3.8 to −45.9%). Qualitatively the shuttle acceleration curves appear dramatically different, although similar average peak accelerations are achieved during use (4.12 vs. 3.47 m/s2, protocol I vs. protocol 2, respectively).
Hip Spasticity and Strength in Children with Spastic Diplegia Cerebral Palsy
Authors: Engsberg Jack R. , Ross Sandy A. , Hollander Kevin W. , Park T.S.
Published: August 2016

Hip spasticity and strength from 44 children with cerebral palsy (CP) and 44 children with able bodies (AB) were compared. For spasticity, a KinCom dynamometer abducted the passive hip at 4 different speeds and recorded the resistive adductor torques. Work values for the torque-angle data were calculated at each speed. Linear regression derived the slope for the line of best fit for the work-velocity data to determine the spasticity measure. For strength, the KinCom rotated the hip from maximum adduction to maximum abduction at a speed of 10°/s while the child performed a maximum abduction concentric contraction. Tests were reversed to record maximum adduction. Maximum torques and work by the abductors and adductors were calculated. Spasticity in the adductors for the CP group was significantly greater than values recorded for the AB group. All strength measures were significantly less than the AB group. Results provide objective information, quantifying hip spasticity and strength in children with CP.
Stretch-Shortening Cycle in Roller Ski Skating: Effects of Speed
Authors: Perrey Stéphane , Millet Guillaume , Candau Robin , Rouillon Jean-Denis
Published: August 2016

The purpose of this study was to examine the effects of speed on the stretch-shortening cycle (SSC) behavior during roller ski skating. Ten highly skilled male cross-country skiers roller skied at 4.56, 5.33 m · s–1and maximal speed using the V2-alternate technique on a flat terrain. Knee and ankle joint kinematics, and EMG of thevastus lateralis(VL) andgastrocnemius lateralis(GL) muscles were recorded during the last 40 s of each bout of roller skiing. Maximal speed was associated with increases in cycle rate combined with decreases in cycle length. For VL, no significant differences were observed for the integrated EMG eccentric-to-concentric ratio (iEMG Ecc/Conc) and for the stretching velocity over the range of speeds. For GL, stretching velocity and iEMG Ecc/Conc were significantly greater at maximal speed. The analysis of GL EMG activity suggests that speed improved GL stiffness so that more elastic energy was stored, a better force transmission occurred, and coupling time decreased. These findings suggest that the efficiency of roller ski skating locomotion may be increased with speed through a better use of the stretch-shortening cycle pattern in the ankle extensors.
Testing the Planar Assumption during Ergometer Cycling
Authors: Umberger Brian R. , Martin Philip E.
Published: August 2016

Lower extremity motions during cycling are often assumed to occur in the sagittal plane. While seemingly logical, this assumption has not been rigorously tested. Frontal plane rotation of the ankle joint (inversion/eversion) has been studied extensively during gait but infrequently during cycling despite the suggestion that excessive eversion or pronation may be related to overuse knee injuries. Two-dimensional sagittal plane hip, knee, and ankle joint kinematics were generally found to be similar to simultaneously measured 3-D values. Despite the similarity in motion patterns, maximum hip angle was 34° more flexed in 2-D than 3-D. Maximum and minimum frontal plane ankle joint angles were similar in 2-D and 3-D. However, during the middle of the pedal cycle, 2-D frontal plane ankle joint motion deviated from 3-D, such that maximum ankle eversion was reached 36% of the pedal cycle later in 2-D versus 3-D. The discrepancy at the hip was due primarily to differences in hip angle definition for 2-D and 3-D approaches, and an alternate convention for hip angle in 2-D is suggested. Discrepancies in frontal plane ankle joint motion are due to weaknesses in the planar approach and would be difficult to overcome without resorting to 3-D measurement.
Within-Day Accommodation Effects on Vertical Reaction Forces for Treadmill Running
Authors: White Scott C. , Gilchrist Louise A. , Christina Kathryn A.
Published: August 2016

Prescribing an appropriate adaptation period is an important consideration when using treadmills for locomotion studies. The present study investigated within-trial accommodation to running on a force measuring treadmill. Force measures were derived from vertical reaction force records of 16 runners; 8 were experienced in running on a treadmill. Three dependent measures, the peak impact force (F1), the loading rate of the impact force (LR), and the peak active force (F2) were tested for significant differences (p < 0.05) every 2 minutes of a continuous 20-min run using a two-factor ANOVA (group × time) with one repeated measure (time). Coefficients of variation (CV) for each dependent measure were tested for statistical significance in the same way. There were no significant differences in F1, LR, or F2 over any samples for the 20-min running trials. There were no significant changes in CV values for the duration of the run. The results from the present study suggest that after 30 seconds of treadmill running, there were no significant within-day accommodation effects on vertical force measures over a 20-min treadmill run. Variability between individuals in the consistency of force measures, however, could be a confounding factor. This lack of consistent response for individuals should be considered when exposing participants to experimental designs involving treadmill locomotion.
Influence of Age, Gender, and Obesity on the Mechanical Properties of the Heel Pad under Walking Impact Conditions
Authors: Alcántara Enrique , Forner Arturo , Ferrús Elena , García Ana-Cruz , Ramiro José
Published: August 2016

Impact mechanics of the human heel pad were studied using a ballistic pendulum. Young and elderly men and women took part in the experiment. Twelve parameters were used to describe heel pad properties. Analysis of variance was conducted to assess the influence of age, gender, and obesity. Heel pad properties were correlated with impact force and time to peak force in order to study impact mechanics. Maximal stiffness, peak displacement, and energy absorption were established so as to sufficiently describe impact properties of the heel pad. Age, gender, and obesity introduced significant differences in heel pad properties. Peak displacement and time to peak force increased in the elderly. Women presented a shorter time to peak force together with lower peak displacement, energy absorption, and lower maximal stiffness than men. Obese elderly showed lower impact forces, longer time to peak, and greater peak displacement than non-obese and younger participants. In addition, energy absorption was greater and maximal stiffness was lower for obese than for non-obese participants.
Effects of Step Uncertainty on Impact Peaks, Shock Attenuation, and Knee/Subtalar Synchrony in Treadmill Running
Authors: Thomas Joshua M. , Derrick Timothy R.
Published: August 2016

The purpose of this research was to determine the effects of step uncertainty on shock attenuation and knee/subtalar synchrony. Uncertainty was manipulated by decreasing the intensity of light and introducing bumps to the running surface. Twelve experienced distance runners ran at their chosen pace on a treadmill with two surfaces (smooth and irregular) and three light intensities (light, medium, dark). Knee angle, subtalar angle, leg impacts, and head impacts were recorded at 1,000 Hz. Heart rate was also monitored. Injury potential was assessed by evaluating the impacts and asynchronous activity between the knee and subtalar joint. Stride length was not influenced by either source of uncertainty. Heart rate increased with the intensity of light on the smooth running surface but decreased with the intensity of light on the irregular surface. The knee was more flexed at heel contact during the irregular surface conditions but was not affected by the intensity of light. This decreased the effective mass of the impact and allowed greater peak leg accelerations and greater impact attenuation during irregular surface running. There was a decrease in the rearfoot angle at contact on the irregular surface that approached significance (p = 0.056). Knee/subtalar asynchrony increased with the intensity of light on the smooth surface but decreased on the irregular surface. It appears that participants used the knee joint to adapt to the irregular surface and thus accommodate changes in the terrain. The subtalar joint may have become more stable during irregular surface running to minimize the chance of inversion sprains. The effects of intensity of light were small and generally mediated the irregular surface effects. Overall, these adaptations likely reduced the potential for injury during irregular surface running but may have been detrimental to performance.
Optimum Technique for Generating Angular Momentum in Accelerated Backward Giant Circles Prior to a Dismount
Authors: Hiley Michael J. , Yeadon M.R.
Published: August 2016

In men’s artistic gymnastics the backward giant circle on the high bar is used to produce the angular momentum that the gymnast needs for executing somersaulting dismounts. Dismounts in which the gymnast performs two somersaults in the layout (straight body) position require the greatest angular momentum. However, it appears there are two distinct techniques that elite gymnasts use when performing backward giant circles prior to a double layout somersault dismount. The “traditional” technique has been superseded by the “scooped” technique which is now used by the majority of elite gymnasts. To determine whether the scooped technique is better at producing angular momentum, a simulation model was used to optimize the angular momentum about the mass center at release. The model was evaluated using data obtained from a force/video analysis of accelerated giant circles. The model was able to estimate the reaction forces measured by strain gauges on the bar to within 9% of the peak forces, and the body rotation angle to within 1% of total rotation. During the optimizations, the joint angle time histories of the model were manipulated in order to maximize the angular momentum about the model’s mass center at release. Two optima were found which were characteristic of the two backward giant circle techniques used by elite gymnasts. The traditional technique produced more angular momentum than the scooped technique, although both were capable of producing sufficient angular momentum for a double layout somersault dismount. This suggests that the preference of elite gymnasts for the scooped technique must be based on factors other than the production of angular momentum.
Mono- and Biarticular Muscle Activity during Jumping in Different Directions
Authors: Jones Stephanie L. , Caldwell Graham E.
Published: August 2016

This study examined the role of mono- and biarticular muscles in control of countermovement jumps (CMJ) in different directions. It was hypothesized that monoarticular muscles would demonstrate the same activity regardless of jump direction, based on previous studies which suggest their role is to generate energy to maximize center-of-mass (CM) velocity. In contrast, biarticular activity patterns were expected to change to control the direction of the ground reaction force (GRF) and CM velocity vectors. Twelve participants performed maximal CMJs in four directions: vertical, forward, intermediate forward, and backward. Electromyographical data from 4 monoarticular and 3 biarticular lower extremity muscles were analyzed with respect to segmental kinematics and kinetics during the jumps. The biarticular rectus femoris (RF), hamstrings (HA), and gastrocnemius all exhibited changes in activity magnitude and pattern as a function of jump angle. In particular, HA and RF demonstrated reciprocal trends, with HA activity increasing as jump angle changed from backward to forward, while RF activity was reduced in the forward jump condition. The vastus lateralis and gluteus maximus both demonstrated changes in activity patterns, although the former was the only monoarticular muscle to change activity level with jump direction. Mono- and biarticular muscle activities therefore did not fit with their hypothesized roles. CM and segmental kinematics suggest that jump direction was initiated early in the countermovement, and that in each jump direction the propulsion phase began from a different position with unique angular and linear momentum. Issues that dictated the muscle activity patterns in each jump direction were the early initiation of appropriate forward momentum, the transition from countermovement to propulsion, the control of individual segment rotations, the control of GRF location and direction, and the influence of the subsequent landing.
A Computer Model to Simulate the Swing Phase of a Transfemoral Prosthesis
Authors: Burkett Brendan , Smeathers James , Barker Timothy M.
Published: August 2016

For amputees to perform an everyday task, or to participate in physical exercise, it is crucial that they have an appropriately designed and functional prosthesis. Past studies of transfemoral amputee gait have identified several limitations in the performance of amputees and in their prosthesis when compared with able-bodied walking, such as asymmetrical gait, slower walking speed, and higher energy demands. In particular the different inertial characteristics of the prosthesis relative to the sound limb results in a longer swing time for the prosthesis. The aim of this study was to determine whether this longer swing time could be addressed by modifying the alignment of the prosthesis. The following hypothesis was tested: Can the inertial characteristics of the prosthesis be improved by lowering the prosthetic knee joint, thereby producing a faster swing time? To test this hypothesis, a simple 2-D mathematical model was developed to simulate the swing-phase motion of the prosthetic leg. The model applies forward dynamics to the measured hip moment of the amputee in conjunction with the inertial characteristics of prosthetic components to predict the swing-phase motion. To evaluate the model and measure any change in prosthetic function, we conducted a kinematic analysis on four Paralympic runners as they ran. When evaluated, there was no significant difference (p> 0.05) between predicted and measured swing time. Of particular interest was how swing time was affected by changes in the position of the prosthetic knee axis. The model suggested that lowering the axis of the prosthetic knee could reduce the longer swing time. This hypothesis was confirmed when tested on the amputee runners.
Patellofemoral Contact Characteristics in Total Knee Prostheses with and Without Anterior Patellar Flange
Authors: Fuchs Susanne , Schuette Guido , Witte, Hartmut , Tibesku Carsten Oliver
Published: August 2016

A new design of total knee prosthesis without anterior patellar flange was developed to preserve the anatomical shape of the patellofemoral joint. The aim of the current study was to experimentally compare patellofemoral contact area and pressure in a nonreplaced knee, in a knee after implantation of a conventionally designed total knee arthroplasty, and in a knee after implantation of the newly designed total knee arthroplasty without patellar flange. Six cadaveric legs were examined before and after implantation of either a conventional or a newly developed total knee arthroplasty, both without patellar replacement. The essential change in design is the absence of an anterior patellar flange. Contact area and pressure were measured using pressure sensitive films in 45°, 60°, 90°, and 120° of flexion and the results were compared between the different prosthesis designs and with the nonreplaced knee. The prosthesis without patellar flange showed less average and maximum pressure than the conventional prosthesis. Compared with the nonreplaced knee, the conventional prosthesis led to increased average and maximum pressure and decreased contact area. In an experimental test setup, the newly developed total knee arthroplasty without patellar flange showed reduced patello-femoral contact pressure in comparison with a total knee prosthesis with conventional patellofemoral design. This could possibly lead to a lower incidence of anterior knee complaints in patients.
Optimal Knee Extension Timing in Springboard and Platform Dives from the Reverse Group
Authors: Sprigings Eric J. , Miller Doris I.
Published: August 2016

Optimized computer simulation, using a mathematical model of a diver, was employed to gain insight into the primary mechanical factors responsible for producing height and rotation in dives from the reverse group. The performance variable optimized was the total angular displacement of the diver as measured from last contact to the point where the diver's mass center passed the level of the springboard or platform. The times of onset, and lengths of activation for the joint torque actuators, were used as the control variables for the optimization process. The results of the platform simulation indicated that the magnitude of the hip torque was approximately twice that generated by the knee joint during the early extension phase of the takeoff. Most of the knee extension for the simulation model coincided with the period of reduced hip torque during the later phase of takeoff, suggesting that the knee torque served mainly to stabilize the lower limbs so that the force from the powerful hip extension could be delivered through to the platform. Maintaining a forward tilt of the lower legs (~50° from the horizontal) during hip and knee extension appeared to be paramount for successful reverse somersaults. Although the movement pattern exhibited by the springboard model was limited by the torque activation strategy employed, the results provided insight into the timing of knee extension. Peak knee extension torque was generated just prior to maximum springboard depression, allowing the diver's muscular efforts to be exerted against a stiffer board. It was also apparent that the diver must maintain an anatomically strong knee position (~140°) at maximum depression to resist the large upward force being exerted by the springboard against the diver's feet. The optimization process suggested that, as the number of reverse somersaults increases, both the angle of the lower legs with respect to the springboard and the angle of knee extension at completion of takeoff should decrease.
Stiffness Adaptations in Shod Running
Authors: Divert Caroline , Baur Heiner , Mornieux Guillaume , Mayer Frank , Belli Alain
Published: August 2016

When mechanical parameters of running are measured, runners have to be accustomed to testing conditions. Nevertheless, habituated runners could still show slight evolutions of their patterns at the beginning of each new running bout. This study investigated runners' stiffness adjustments during shoe and barefoot running and stiffness evolutions of shoes. Twenty-two runners performed two 4-minute bouts at 3.61 m·s–1shod and barefoot after a 4-min warm-up period. Vertical and leg stiffness decreased during the shoe condition but remained stable in the barefoot condition,p< 0.001. Moreover, an impactor test showed that shoe stiffness increased significantly during the first 4 minutes,p< 0.001. Beyond the 4th minute, shoe properties remained stable. Even if runners were accustomed to the testing condition, as running pattern remained stable during barefoot running, they adjusted their leg and vertical stiffness during shoe running. Moreover, as measurements were taken after a 4-min warm-up period, it could be assumed that shoe properties were stable. Then the stiffness adjustment observed during shoe running might be due to further habituations of the runners to the shod condition. To conclude, it makes sense to run at least 4 minutes before taking measurements in order to avoid runners' stiffness alteration due to shoe property modifications. However, runners could still adapt to the shoe.