bluuebunny/crossref_metadata_2025 huggingface dataset:
The Force-Length Curves of the Human Rectus Femoris and Gastrocnemius Muscles in Vivo
Authors: Winter Samantha L. , Challis John H.
Published: August 2016

For a physiologically realistic joint range of motion and therefore range of muscle fiber lengths, only part of the whole muscle force-length curve can be used in vivo; that is, only a section of the force-length curve is expressed. Previous work has determined that the expressed section of the force-length curve for individual muscles can vary between subjects; however, the degree of intersubject variability is different for different muscles. This study determined the expressed section of both the rectus femoris and gastrocnemius—muscles with very different ratios of tendon slack length to muscle fiber optimum length—for 28 nonspecifically trained subjects to test the hypothesis that the value of this ratio affects the amount of variability in the expressed section. The force-length curves of the two muscles were reconstructed from moment-angle data using the method of Herzog & ter Keurs (1988). There was no relationship between the expressed sections of the force-length curve for the two muscles. Less variability was found in the expressed section of the gastrocnemius compared with the rectus femoris, supporting the hypothesis. The lack of relationship between the expressed sections of the two muscles has implications for motor control and for training muscle for rehabilitation.
Three-Dimensional Trunk Kinematics and Low Back Pain in Elite Female Fast Bowlers
Authors: Stuelcken Max C. , Ferdinands René E.D. , Sinclair Peter J.
Published: August 2016

This study aimed to investigate the bowling techniques of female fast bowlers and identify any association between a history of low back pain (LBP) and the movement patterns of the thorax relative to the pelvis during the delivery stride of the bowling action. Three-dimensional kinematic data were collected from 26 elite Australian female fast bowlers using an eight-camera Vicon motion analysis system. Nineteen bowlers used a mixed action, 6 bowlers used a semiopen action, and 1 bowler used a side-on action. Fourteen bowlers had a history of LBP. Eight of these 14 bowlers used a mixed action, and bowlers with more shoulder counterrotation were no more likely to have a history of LBP. Bowlers with a history of LBP positioned the thorax in more left lateral flexion relative to the pelvis between 73–79% of the delivery stride, and moved the thorax through a significantly greater range of lateral flexion relative to the pelvis during the delivery stride compared with bowlers with no history of LBP. This information will give coaches and support staff a better understanding of female bowling technique and may facilitate better screening practices for elite female cricketers.
External Effects in the 400-m Hurdles Race
Authors: Quinn Mike D.
Published: August 2016

A mathematical model based on a differential equation of motion is used to simulate the 400-m hurdles race for men and women. The model takes into account the hurdler’s stride pattern, the hurdle clearance, and aerobic and anaerobic components of the propulsive force of the athlete, as well as the effects of wind resistance, altitude of the venue, and curvature of the track. The model is used to predict the effect on race times of different wind conditions and altitudes. The effect on race performance of the lane allocation and the efficiency of the hurdle clearance is also predicted. The most favorable wind conditions are shown to be a wind speed no greater than 2 m/s assisting the athlete in the back straight and around the second bend. The outside lane (lane 8) is shown to be considerably faster than the favored center lanes. In windless conditions, the advantage can be as much as 0.15 s for men and 0.12 s for women. It is shown that these values are greatly affected by the wind conditions.
Quantitative Analysis of the Limits of Stability in Sitting
Authors: Preuss Richard A. , Popovic Milos R.
Published: August 2016

This study defines the limits of stability in sitting, and quantitatively assesses two measures of postural control relative to these limits. Young, healthy subjects sat, feet unsupported, on an elevated force plate. The limits of stability were determined by a least square fit of an ellipse to the center of pressure (CoP) excursion during maximal leaning in 8 directions. These were highly symmetrical and centered within the base of support. The ellipses had a mean eccentricity of 0.66 (major axis in the sagittal plane) and covered an area approx. 1/3 of the base of support. The CoP was then monitored over 4 min of quiet sitting, during which the postural sway covered an area <0.05% of the limits of stability and was closely centered within the latter. Finally, target-directed trunk movements were performed, in 5 directions, at 4 movement speeds and 3 target distances. Increased target distance and movement speed both decreased the margin of stability (distance between the CoP and the limits of stability), as did movement in the frontal plane, reflecting the eccentricity of the limits of stability. These combined findings support the validity of this quantitative method of defining the limits of stability in sitting, for healthy individuals.
Responses of the Trunk to Multidirectional Perturbations during Unsupported Sitting in Normal Adults
Authors: Thrasher T. Adam , Sin Vivian W. , Masani Kei , Vette Albert H. , Craven B. Cathy , Popovic Milos R.
Published: August 2016

Understanding how the human body responds to unexpected force perturbations during quiet sitting is important to the science of motor behavior and the design of neuroprostheses for sitting posture. In this study, the performance characteristics of the neck and trunk in healthy individuals were assessed by measuring the kinematic responses to sudden, unexpected force perturbations applied to the thorax. Perturbations were applied in eight horizontal directions. It was hypothesized that displacement of the trunk, settling time and steady-state error would increase when the perturbation direction was diagonal (i.e., anterior-lateral or posterior-lateral) due to the increased complexity of asymmetrical muscle responses. Perturbation forces were applied manually. The neck and trunk responded in a synchronized manner in which all joints achieved peak displacement simultaneously then returned directly to equilibrium. Displacement in the direction of perturbation and perpendicular to the direction of perturbation were both significantly greater in response to diagonal perturbations (p < .001). The center of mass returned to equilibrium in 3.64 ± 1.42 s after the onset of perturbation. Our results suggest that the trunk sometimes behaves like an underdamped oscillator and is not controlled by simple stiffness when subjected to loads of approximately 200 N. The results of this study are intended to be used to develop a neuroprosthesis for artificial control of trunk stability in individuals with spinal cord injury.
Variability and Symmetry of Force Platform Variables in Maximum-Speed Running in Young and Older Athletes
Authors: Korhonen Marko T. , Suominen Harri , Viitasalo Jukka T. , Liikavainio Tuomas , Alen Markku , Mero Antti A.
Published: August 2016

Eighteen young (23 ± 4 yr) and 25 older (70 ± 4 yr) male sprinters were examined for ground reaction force (GRF) and temporal-spatial variables. The data were collected during maximum-speed phase, and variability and symmetry indices were calculated from a total of 8 steps. There was little variation (CV < 6%) in vertical and resultant GRF and kinematic variables, while impact loading had high variability (CV: 10–21%). Overall, the pattern of variability was similar in both groups. Yet, a small but significant age-related increase in CV was evident in horizontal GRFs. There was a variable-specific asymmetry between legs but it was not related to leg dominance. No age differences existed in the symmetry indices. Results indicate that only selected force platform variables are symmetric and repeatable enough so that their use for comparison purposes is appropriate. Data also suggest that aging may increase variability in certain biomechanical measures, whereas symmetry is not affected by age.
Influence of Custom Foot Orthotic Intervention on Lower Extremity Intralimb Coupling during a 30-Minute Run
Authors: MacLean Christopher L. , van Emmerik Richard , Hamill Joseph
Published: August 2016

The purpose of this study was to analyze the influence of a custom foot orthotic (CFO) intervention on lower extremity intralimb coupling during a 30-min run in a group of injured runners and to compare the results to a control group of healthy runners. Three-dimensional kinematic data were collected during a 30-min run on healthy female runners (Shoe-only) and a group of female runners who had a recent history of overuse injury (Shoe-only and Shoe with custom foot orthoses). Results from the study revealed that the coordination variability and pattern for the some couplings were influenced by history of injury, foot orthotic intervention and the duration of the run. These data suggest that custom foot orthoses worn by injured runners may play a role in the maintenance of coordination variability of the tibia (transverse plane) and calcaneus (frontal plane) coupling during the Early Stance phase. In addition, it appears that the coupling angle between the knee (transverse plane) and rearfoot (frontal plane) joints becomes more symmetrical in the late stance phase as a run progresses.
High-Level Swimmers’ Kinetic Efficiency during the Underwater Phase of a Grab Start
Authors: Elipot Marc , Dietrich Gilles , Hellard Philippe , Houel Nicolas
Published: August 2016

The purpose of the present work was to study swimmers’ efficiency during the underwater phase of the grab start. Eight high-level swimmers participated in this study. They performed two types of start: a regular grab start (with underwater leg propulsion after the glide) and a grab start with no underwater movement (swimmers had to remain in a streamlined position). Four cameras filmed the entire underwater phase of all starts. Nine anatomic landmarks were identified on the swimmers’ bodies and their positions were calculated using a modified double plan DLT technique. From these positions and Dempster’s anthropometric data, the center of mass position and velocity were also determined. Kinetic energies were also calculated. This velocity and kinetic energies for the two types of start were compared. Swimmers began underwater leg propulsion 1.69 m too soon. The global and internal energies were significantly higher for the start with underwater leg propulsion. Nevertheless, swimmers’ velocities were equivalent for both starts. These results suggest that the swimmers did not use the underwater phase of the start efficiently: By kicking too soon, they did not succeed in producing higher velocities and thus wasted energy.
Pelvic Kinematic Method for Determining Vertical Jump Height
Authors: Chiu Loren Z.F. , Salem George J.
Published: August 2016

Sacral marker and pelvis reconstruction methods have been proposed to approximate total body center of mass during relatively low intensity gait and hopping tasks, but not during a maximum effort vertical jumping task. In this study, center of mass displacement was calculated using the pelvic kinematic method and compared with center of mass displacement using the ground-reaction force-impulse method, in experienced athletes (n = 13) performing restricted countermovement vertical jumps. Maximal vertical jumps were performed in a biomechanics laboratory, with data collected using an 8-camera motion analysis system and two force platforms. The pelvis center of mass was reconstructed from retro-reflective markers placed on the pelvis. Jump height was determined from the peak height of the pelvis center of mass minus the standing height. Strong linear relationships were observed between the pelvic kinematic and impulse methods (R2 = .86; p < .01). The pelvic kinematic method underestimated jump height versus the impulse method, however, the difference was small (CV = 4.34%). This investigation demonstrates concurrent validity for the pelvic kinematic method to determine vertical jump height.
Relationship Between Eccentric Hip Torque and Lower-Limb Kinematics: Gender Differences
Authors: Baldon Rodrigo de Marche , Lobato Daniel Ferreira Moreira , Carvalho Lívia Pinheiro , Santiago Paulo Roberto Pereira , Benze Benedito Galvão , Serrão Fábio Viadanna
Published: August 2016

The purposes of this study were to compare lower-limb kinematics between genders, and determine the relationships among eccentric hip abductor and lateral rotator torques and lower-limb kinematics. The movements of the pelvis, femur, and knee were calculated for 16 women and 16 men during the single-leg squat. Eccentric hip abductor and lateral rotator torques were measured using an isokinetic dynamometer. The results showed that women had greater contralateral pelvic depression, femur adduction, and knee abduction than men. The eccentric hip abductor and lateral rotator torques were correlated with coronal plane femur and knee movements in the overall sample. When the genders were analyzed separately, it was observed that women with greater eccentric hip abductor torque exhibited less femur adduction and femur medial rotation, and greater knee adduction excursion. No significant relationship was observed between the isokinetic and kinematic variables in the male group. The differences between the genders help to explain the greater rate of knee disorders observed in women. Moreover, the eccentric hip abduction action seemed to be more important in women to control the lower-limb movements.
Direct Kinematic Modeling of the Upper Limb During Trunk-Assisted Reaching
Authors: Hanneton Sylvain , Dedobbeler Svetlana , Hoellinger Thomas , Roby-Brami Agnès
Published: August 2016

The study proposes a rigid-body biomechanical model of the trunk and whole upper limb including scapula and the test of this model with a kinematic method using a six-dimensional (6-D) electromagnetic motion capture (mocap) device. Large unconstrained natural trunk-assisted reaching movements were recorded in 7 healthy subjects. The 3-D positions of anatomical landmarks were measured and then compared to their estimation given by the biomechanical chain fed with joint angles (the direct kinematics). Thus, the prediction errors was attributed to the different joints and to the different simplifications introduced in the model. Large (approx. 4 cm) end-point prediction errors at the level of the hand were reduced (to approx. 2 cm) if translations of the scapula were taken into account. As a whole, the 6-D mocap seems to give accurate results, except for pronosupination. The direct kinematic model could be used as a virtual mannequin for other applications, such as computer animation or clinical and ergonomical evaluations.
Trigonometric Analysis of the Mechanical Axis Deviation Induced by Telescopic Intramedullary Femoral Lengthening Nails
Authors: Burghardt Rolf D. , Herzenberg John E. , Burghardt Manfred H.
Published: August 2016

Femoral lengthening with intramedullary nails can create alterations in the mechanical axis of the limb. This is based on the relationship of the anatomic femur axis to the mechanical femur axis, which is typically 5–9 degrees valgus. We developed trigonometric formulas to calculate the predicted change, using the lengths of the tibia, femur, and whole limb; the amount of lengthening; and the angle between the anatomic and the mechanical axis of the femur. We recognized three patterns depending on whether the overall limb mechanical axis is lateral (valgus), medial (varus), or straight through the center of the knee. The varus and valgus patterns lead to similar formulas. When the mechanical axis goes directly through the center of the knee joint, the formula simplifies. These formulas could be incorporated into digital radiographic programs to predict the change in mechanical axis deviation that will develop from lengthening along the anatomic femur axis with an intramedullary lengthening nail.
The Effect of Cost Function on Optimum Technique of the Undersomersault on Parallel Bars
Authors: Hiley Michael J. , Yeadon Maurice R.
Published: August 2016

The undersomersault, or felge, to handstand on parallel bars has become an important skill in Men’s Artistic Gymnastics as it forms the basis of many complex variations. To receive no deductions from the judges, the undersomersault must be performed without demonstrating the use of strength to achieve the final handstand position. Two male gymnasts each performed nine undersomersaults from handstand to handstand while data were recorded using an automatic motion capture system. The highest and lowest scoring trials of each gymnast, as determined by four international judges, were chosen for further analysis. Three optimization criteria were used to generate undersomersault technique during the swing phase of the skill using a computer simulation model: minimization of peak joint torques, minimization of horizontal velocity before release, and maximization of angular momentum. The techniques used by both gymnasts could be explained using the second optimization criterion which facilitated further skill development. The first optimization criterion generated a technique advocated for beginners where strength might be expected to be a limiting factor. The third optimization criterion resulted in a different type of undersomersault movement of greater difficulty according to the FIG Code of Points.
Mathematical Model to Predict Drivers’ Reaction Speeds
Authors: Long Benjamin L. , Gillespie A. Isabella , Tanaka Martin L.
Published: August 2016

Mental distractions and physical impairments can increase the risk of accidents by affecting a driver’s ability to control the vehicle. In this article, we developed a linear mathematical model that can be used to quantitatively predict drivers’ performance over a variety of possible driving conditions. Predictions were not limited only to conditions tested, but also included linear combinations of these tests conditions. Two groups of 12 participants were evaluated using a custom drivers’ reaction speed testing device to evaluate the effect of cell phone talking, texting, and a fixed knee brace on the components of drivers’ reaction speed. Cognitive reaction time was found to increase by 24% for cell phone talking and 74% for texting. The fixed knee brace increased musculoskeletal reaction time by 24%. These experimental data were used to develop a mathematical model to predict reaction speed for an untested condition, talking on a cell phone with a fixed knee brace. The model was verified by comparing the predicted reaction speed to measured experimental values from an independent test. The model predicted full braking time within 3% of the measured value. Although only a few influential conditions were evaluated, we present a general approach that can be expanded to include other types of distractions, impairments, and environmental conditions.
Evaluation of Fatigue of Respiratory and Lower Limb Muscles During Prolonged Aerobic Exercise
Authors: Nadiv Yaara , Vachbroit Ricki , Gefen Amit , Elad David , Zaretsky Uri , Moran Dani , Halpern Pinchas , Ratnovsky Anat
Published: August 2016

The respiratory muscles may fatigue during prolonged exercises and thereby become a factor that limits extreme physical activity. The aim of the current study was to determine whether respiratory muscle fatigue imposes a limitation on extreme physical activity of well-trained young men. Electromyography (EMG) signals of respiratory (external intercostal and sternomastoid) and calf muscles (gastrocnemius) were measured (N = 8) during 1 hr of treadmill marching at a speed of 8 km/hr with and without a 15 kg backpack. The root mean square (RMS) and the mean power frequency of the EMG signals were evaluated for calculating fatigue indices. The EMG RMS revealed that the respiratory and calf muscles did not fatigue during the marching without a backpack load. The study did show, however, a significant rise in the EMG values when a backpack was carried with respect to the no-load condition (p < .05), which suggests that respiratory muscles should be trained in military recruits who are required to carry loaded backpacks while marching.
Aerodynamics of Cyclist Posture, Bicycle and Helmet Characteristics in Time Trial Stage
Authors: Chabroux Vincent , Barelle Caroline , Favier Daniel
Published: August 2016

The present work is focused on the aerodynamic study of different parameters, including both the posture of a cyclist’s upper limbs and the saddle position, in time trial (TT) stages. The aerodynamic influence of a TT helmet large visor is also quantified as a function of the helmet inclination. Experiments conducted in a wind tunnel on nine professional cyclists provided drag force and frontal area measurements to determine the drag force coefficient. Data statistical analysis clearly shows that the hands positioning on shifters and the elbows joined together are significantly reducing the cyclist drag force. Concerning the saddle position, the drag force is shown to be significantly increased (about 3%) when the saddle is raised. The usual helmet inclination appears to be the inclination value minimizing the drag force. Moreover, the addition of a large visor on the helmet is shown to provide a drag coefficient reduction as a function of the helmet inclination. Present results indicate that variations in the TT cyclist posture, the saddle position and the helmet visor can produce a significant gain in time (up to 2.2%) during stages.
A Comparison of Ballistic and Nonballistic Lower-Body Resistance Exercise and the Methods Used to Identify Their Positive Lifting Phases
Authors: Lake Jason , Lauder Mike , Smith Neal , Shorter Kathleen
Published: August 2016

This study compared differences between ballistic jump squat (B) and nonballistic back squat (NB) force, velocity, power, and relative acceleration duration, and the effect that the method used to identify the positive lifting phase had on these parameters. Ground reaction force and barbell kinematics were recorded from 30 resistance trained men during B and NB performance with 45% 1RM. Force, velocity, and power was averaged over positive lifting phases identified using the traditional peak barbell displacement (PD) and positive impulse method. No significant differences were found between B and NB mean force, and mean power, but B mean velocity was 14% greater than the NB equivalent. Positive impulse mean force was 24% greater than PD mean force, and B relative acceleration duration was 8.6% greater than the NB equivalent when PD was used to identify the end of the positive lifting phase. These results challenge common perceptions of B superiority for power development.
Limb Dominance Related to the Variability and Symmetry of the Vertical Ground Reaction Force and Center of Pressure
Authors: Wang Yun , Watanabe Kazuhiko
Published: August 2016

The notion of limb dominance has been commonly used in the upper extremity, yet the two lower extremities are often treated as equal for analytical purposes. Attempts to determine the effects of limb laterality on gait have produced conflicting results. The purpose of this study was to determine if limb dominance affects the vertical ground reaction force and center of pressure (COP) during able-bodied gait. The Parotec system (Paromed GmbH, Germany) was used to collect plantar foot pressure data. Fifteen subjects volunteered to participate in this study. The coefficient of variation of the COP displacement in the mediolateral direction and the variability of peak force beneath the lateral forefoot in the nondominant foot were significant greater than in the dominant foot. Moreover, COP velocity in the anterior-posterior direction during the terminal stance phase showed greater value in the dominant foot. Our study provides support for limb laterality by showing limb dominance affected the vertical ground reaction force and center of pressure during walking gait. This finding suggests it is an important issue in movement science for clinicians and would assist in improving sports performance and rehabilitation program.
Walking Strategies Change With Distance From Hill Transition and Scale With Hill Angle
Authors: Sheehan Riley C. , Gottschall Jinger S.
Published: August 2016

Individuals must constantly modify their gait patterns to safely transition between different surfaces. The goal of the current study was to determine if gait changes could be detected two steps from a transition, and whether these changes scaled with the angle of the hill. We hypothesized that during the anticipation of uphill walking and the aftereffect of downhill walking, the magnitude of kinetic and electromyography changes would be greatest at steep hill angles and fewer steps from the transition. We collected force and electromy-ography data as participants walked on the level ground before an uphill ramp and after a downhill ramp. As hypothesized, there were significant main effects for both the number of steps and angle of the hill for the first vertical GRF peak, as well as lateral gastrocnemius and vastus lateralis activity. Overall, our results indicate that when transitioning to and from hills, anticipation and aftereffect responses occur at least two steps from the transition and are scaled to the angle of the hill.
Effect of Hopping Frequency on Bilateral Differences in Leg Stiffness
Authors: Hobara Hiroaki , Inoue Koh , Kanosue Kazuyuki
Published: August 2016

Understanding the degree of leg stiffness during human movement would provide important information that may be used for injury prevention. In the current study, we investigated bilateral differences in leg stiffness during one-legged hopping. Ten male participants performed one-legged hopping in place, matching metronome beats at 1.5, 2.2, and 3.0 Hz. Based on a spring-mass model, we calculated leg stiffness, which is defined as the ratio of maximal ground reaction force to maximum center of mass displacement at the middle of the stance phase, measured from vertical ground reaction force. In all hopping frequency settings, there was no significant difference in leg stiffness between legs. Although not statistically significant, asymmetry was the greatest at 1.5 Hz, followed by 2.2 and 3.0 Hz for all dependent variables. Furthermore, the number of subjects with an asymmetry greater than the 10% criterion was larger at 1.5 Hz than those at 2.2 and 3.0 Hz. These results will assist in the formulation of treatment-specific training regimes and rehabilitation programs for lower extremity injuries.
Interactive Effects of Joint Angle, Contraction State and Method on Estimates of Achilles Tendon Moment Arms
Authors: Fath Florian , Blazevich Anthony J. , Waugh Charlie M. , Miller Stuart C. , Korff Thomas
Published: August 2016

The muscle-tendon moment arm is an important input parameter for musculoskeletal models. Moment arms change as a function of joint angle and contraction state and depend on the method being employed. The overall purpose was to gain insights into the interactive effects of joint angle, contraction state and method on the Achilles tendon moment arm using the center of rotation (COR) and the tendon excursion method (TE). Achilles tendon moment arms were obtained at rest (TErest, CORrest) and during a maximum voluntary contraction (CORMVC) at four angles. We found strong correlations between TErest and CORMVC for all angles (.72 ≤ r ≤ .93) with Achilles tendon moment arms using CORMVC being 33–36% greater than those obtained from TErest. The relationship between Achilles tendon moment arms and angle was similar across both methods and both levels of muscular contraction. Finally, Achilles tendon moment arms for CORMVC were 1–8% greater than for CORrest.
A Viscoelastic Constitutive Model Can Accurately Represent Entire Creep Indentation Tests of Human Patella Cartilage
Authors: Keenan Kathryn E. , Pal Saikat , Lindsey Derek P. , Besier Thor F. , Beaupre Gary S.
Published: August 2016

Cartilage material properties provide important insights into joint health, and cartilage material models are used in whole-joint finite element models. Although the biphasic model representing experimental creep indentation tests is commonly used to characterize cartilage, cartilage short-term response to loading is generally not characterized using the biphasic model. The purpose of this study was to determine the short-term and equilibrium material properties of human patella cartilage using a viscoelastic model representation of creep indentation tests. We performed 24 experimental creep indentation tests from 14 human patellar specimens ranging in age from 20 to 90 years (median age 61 years). We used a finite element model to reproduce the experimental tests and determined cartilage material properties from viscoelastic and biphasic representations of cartilage. The viscoelastic model consistently provided excellent representation of the short-term and equilibrium creep displacements. We determined initial elastic modulus, equilibrium elastic modulus, and equilibrium Poisson’s ratio using the viscoelastic model. The viscoelastic model can represent the short-term and equilibrium response of cartilage and may easily be implemented in whole-joint finite element models.
Age-Related Differences in Center of Pressure Measures During One-Leg Stance Are Time Dependent
Authors: Parreira Rodolfo B. , Boer Marcela C. , Rabello Lucas , Costa Viviane de Souza P. , de Oliveira Eros , da Silva Rubens A.
Published: August 2016

The aim of this study was to evaluate the changes in center of pressure (COP) movement in four time intervals (5, 10, 15 and 30 s) during a one-leg stance test performed by young and elderly adults. Twelve young adults (mean 20 years) and 12 elderly subjects (mean 68 years) participated in this study. The subjects performed three 30 s trials of an eyes open one-leg stance test on a force platform, in which the COP parameter was computed at four points in time from same original COP signal. Significant differences were found between the young and elderly adults (P < .007) only at the 10, 15 and 30 s intervals. For both groups, COP changes were significantly different between the 5 s time interval and other intervals (10, 15 and 30 s). In conclusion, these results pointed out that age-related difference in COP changes were time dependent. This suggests that the use of longer durations increases the possibility of distinguishing more subtle differences in postural strategy among different groups of subjects.
A Biomechanical Study of Side Steps at Different Distances
Authors: Inaba Yuki , Yoshioka Shinsuke , Iida Yoshiaki , Hay Dean C. , Fukashiro Senshi
Published: August 2016

Lateral quickness is a crucial component of many sports. However, biomechanical factors that contribute to quickness in lateral movements have not been understood well. Thus, the purpose of this study was to quantify 3-dimensional kinetics of hip, knee, and ankle joints in side steps to understand the function of lower extremity muscle groups. Side steps at nine different distances were performed by nine male subjects. Kinematic and ground reaction force data were recorded, and net joint torque and work were calculated by a standard inverse-dynamics method. Extension torques and work done at hip, knee, and ankle joints contributed substantially to the changes in side step distances. On the other hand, hip abduction work was not as sensitive to the changes in the side step distances. The main roles of hip abduction torque and work were to accelerate the center of mass laterally in the earlier phase of the movement and to keep the trunk upright, but not to generate large power for propulsion.
Kinetic Sensitivity of a New Lumbo-Pelvic Model to Variation in Segment Parameter Input
Authors: Crewe Helen , Campbell Amity , Elliott Bruce , Alderson Jacqueline
Published: August 2016

This study aimed to assess variability in lumbo-pelvic forces and moments during a dynamic high-impact activity (cricket fast bowling) when calculated using different body segment parameters (BSPs). The first three BSPs were estimated using methods where the trunk was divided into segments according to nonspinal anatomical landmarks. The final approach defined segment boundaries according to vertebral level. Three-dimensional motion analysis data from nine male cricketers’ bowling trials were processed using the four BSPs. A repeated-measures analysis of variance revealed no significant effect on peak lumbo-pelvic forces. However, the segmentation approach based on vertebral level resulted in significantly larger peak flexion and lateral flexion moments than the other BSP data sets. This has implications for comparisons between studies using different BSPs. Further, given that a method defined with reference to vertebral level more closely corresponds with relevant anatomical structures, this approach may more accurately reflect lumbar moments.
Gender Differences in Lower Limb Kinematics During Stair Descent
Authors: de M. Baldon Rodrigo , Lobato Daniel F.M. , Furlan Leonardo , Serrão Fábio
Published: August 2016

The purpose of this study was to compare lower limb kinematics between genders during stair descent. Fifteen females and fifteen males who were healthy and active were included in this study. The lower limb kinematics (pelvis, femur and knee) in the coronal and transversal planes were assessed during stair descent at 30°, 40°, 50° and 60° of knee flexion. The study found that females showed greater knee medial rotation for all the knee flexion angles (P = .02−.001), greater femoral adduction (P = .01 for all variables), with exception for 30° (P = .13), and greater femoral lateral rotation at 60° (P = .04). Females also showed a trend to have greater knee valgus at all the knee flexion angles (P = .06−.11) as well as less contralateral pelvis elevation at 50° and 60° (P = .10 and .12, respectively). This study showed that females carry out the stair descent with a lower limb alignment that might predispose them to develop overuse knee injuries, such as the iliotibial band syndrome and patellofemoral pain syndrome. Further prospective investigations should be carried out to verify whether these variables are factors that could predict these knee injuries.
Achilles Tendon Mechanical Properties After Both Prolonged Continuous Running and Prolonged Intermittent Shuttle Running in Cricket Batting
Authors: Houghton Laurence , Dawson Brian , Rubenson Jonas
Published: August 2016

Effects of prolonged running on Achilles tendon properties were assessed after a 60 min treadmill run and 140 min intermittent shuttle running (simulated cricket batting innings). Before and after exercise, 11 participants performed ramp-up plantar flexions to maximum-voluntary-contraction before gradual relaxation. Muscle-tendon-junction displacement was measured with ultrasonography. Tendon force was estimated using dynamometry and a musculoskeletal model. Gradients of the ramp-up force-displacement curves fitted between 0–40% and 50–90% of the preexercise maximal force determined stiffness in the low- and high-force-range, respectively. Hysteresis was determined using the ramp-up and relaxation force-displacement curves and elastic energy storage from the area under the ramp-up curve. In simulated batting, correlations between tendon properties and shuttle times were also assessed. After both protocols, Achilles tendon force decreased (4% to 5%, P < .050), but there were no changes in stiffness, hysteresis, or elastic energy. In simulated batting, Achilles tendon force and stiffness were both correlated to mean turn and mean sprint times (r = −0.719 to −0.830, P < .050). Neither protocol resulted in fatigue-related changes in tendon properties, but higher tendon stiffness and plantar flexion force were related to faster turn and sprint times, possibly by improving force transmission and control of movement when decelerating and accelerating.
Changes in Kinematics, Metabolic Cost, and External Work During Walking with a Forward Assistive Force
Authors: Zirker Christopher A. , Bennett Bradford C. , Abel Mark F.
Published: August 2016

We examined how the application of a forward horizontal force applied at the waist alters the metabolic cost, kinematics, and external work of gait. Horizontal assist forces of 4%, 8% and 12% of a subject’s body weight were applied via our testing apparatus while subjects walked at comfortable walking speed on a level treadmill. Kinematic and metabolic parameters were measured using motion capture and ergospirometry respectively on a group of 10 healthy male subjects. Changes in kinematic and metabolic parameters were quantified and found similar to walking downhill at varying grades. A horizontal assist force of 8% resulted in the greatest reduction of metabolic cost. Changes in recovery factor, external work, and center of mass (COM) movement did not correlate with changes in metabolic rate and therefore were not driving the observed reductions in cost. The assist force may have performed external work by providing propulsion as well as raising the COM as it pivots over the stance leg. Assist forces may decrease metabolic cost by reducing the concentric work required for propulsion while increasing the eccentric work of braking. These findings on the effects of assist forces suggest novel mobility aids for individuals with gait disorders and training strategies for athletes.
Influence of the Hip Flexion Angle on Isokinetic Hip Rotator Torque and Acceleration Time of the Hip Rotator Muscles
Authors: Baldon Rodrigo de M. , Furlan Leonardo , Serrão Fábio V.
Published: August 2016

The purpose of this study was to verify the influence of the hip flexion angle on isokinetic rotator torque and acceleration times of the hip medial and lateral rotator muscles. Twenty-one healthy women were included in this study. The hip rotator function was evaluated at 3 different hip flexion angles (10°, 40°, and 90°). The results showed that both eccentric and concentric hip lateral rotator torques were greater at 40° of hip flexion when compared with 90°. Moreover, both the eccentric and concentric hip medial rotator torques were greater at 90° of hip flexion than at 40° and 10°, and greater at 40° than at 10°. In addition, both the eccentric and concentric hip medial to lateral rotator torque ratios were greater at 90° of hip flexion than at 40° and 10°, and greater at 40° than at 10°. Finally, the acceleration times of the hip medial rotator muscles were smaller at 90° of hip flexion than at 10° and smaller at 40° than at 10°. The current results highlight the importance of evaluating the hip rotator muscles at different hip flexion angles to comprehensively assess their functions.
Mechanomyographic Responses for the Biceps Brachii Are Unable to Track the Declines in Peak Torque During 25, 50, 75, and 100 Fatiguing Isokinetic Muscle Actions
Authors: Stock Matt S. , Beck Travis W. , DeFreitas Jason M. , Ye Xin
Published: August 2016

This study examined the peak torque and mechanomyographic (MMG) amplitude and mean frequency (MNF) responses during fatiguing isokinetic muscle actions. On four separate occasions, twenty men (mean ± SD age = 23 ± 3 years) performed 25, 50, 75, and 100 repeated maximal concentric isokinetic muscle actions of the dominant forearm flexors. During each muscle action, the MMG signal was detected from the biceps brachii with an accelerometer. The data were examined with linear regression and one-way repeated measures analyses of variance. The results indicated that the mean percent decline in peak torque value for the 25 repetition trial (25.6%) was significantly less than that for the 50 repetition trial (45.2%). Furthermore, the mean linear slope coefficient for the peak torque versus repetition number relationship for the 50 repetition trial was significantly less than that for the 100 repetition trial. There were no mean differences among the trials for the linear slope coefficients and y-intercepts for the MMG amplitude and MNF versus repetition number relationships. When detected with an accelerometer, the linear slope coefficients and y-intercepts for the MMG amplitude and MNF versus repetition number relationships were not sensitive enough to track the decline in muscle function during fatigue.
A New Postural Force Production Index to Assess Propulsion Effectiveness During Handcycling
Authors: Jacquier-Bret Julien , Faupin Arnaud , Rezzoug Nasser , Gorce Philippe
Published: August 2016

The aim of this study was to propose a new index called Postural Force Production Index (PFPI) for evaluating the force production during handcycling. For a given posture, it assesses the force generation capacity in all Cartesian directions by linking the joint configuration to the effective force applied on the handgrips. Its purpose is to give insight into the force pattern of handcycling users, and could be used as ergonomic index. The PFPI is based on the force ellipsoid, which belongs to the class of manipulability indices and represents the overall force production capabilities at the hand in all Cartesian directions from unit joint torques. The kinematics and kinetics of the arm were recorded during a 1-min exercise test on a handcycle at 70 revolutions per minute performed by one paraplegic expert in handcycling. The PFPI values were compared with the Fraction Effective Force (FEF), which is classically associated with the effectiveness of force application. The results showed a correspondence in the propulsion cycle between FEF peaks and the most favorable postures to produce a force tangential to the crank rotation (PFPI). This preliminary study opens a promising way to study patterns of force production in the framework of handcycling movement analysis.
The Relationship between the Coefficient of Restitution and Energy Losses in Tennis Rackets
Authors: Hatze Herbert
Published: August 2016

The relationship is investigated between the apparent coefficient of restitution and the losses in preimpact kinetic energy of the ball for tennis rackets whose handles are constrained by various clamping modes. The complete energy balance equation of the racket-ball system is derived, and experimental results involving four test rackets are then used to evaluate the various components of the total energy loss for the standardized hand-held mode and the vice-clamping mode. Results demonstrate that the apparent coefficient of restitution is not, as previously thought, independent of the clamping mode but varies significantly with the constraining condition applied to the handle, and with the preimpact velocity of the ball. The relative energy losses in the strings are comparatively small, whereas the losses in the ball increase exponentially with the magnitude of the impulse. The major part of the total loss in kinetic energy of the impacting ball is due to the spatial postimpact recoil motion and internal vibrations of the racket frame.
Body Segment Moments of Inertia of the Elderly
Authors: Jensen Robert K. , Fletcher Paula
Published: August 2016

The segment principal moments of inertia of a sample of 7 elderly males and 12 elderly females were estimated using a model based on stacked elliptical cylinders at 2-cm intervals. Apart from the thigh, all male parameters were larger than female parameters. The largest differences were for the lower trunk and hand and for the forearm. The inertia parameters of the thigh for the males were about 12% smaller than the females. Nonlinear estimations of segment principal moments were then determined. The effect of the differences was tested by cross validating cadaver results against the elliptical model results. The regressions were then cross validated using an independent sample of 6 subjects. The standard errors of fit given as a percentage of the mean, Sf, were smaller than the cross validation results for the cadaver regressions and the differences were attributed to differences between cadavers and living subjects.
Aging, Respiratory Function, and Exercise
Authors: Shephard Roy J.
Published: August 2016

Aging leads to a progressive deterioration of lung function, including a decrease of vital capacity, an increase of residual volume, a tendency for the airways to collapse during expiration, enlargement of all components of the respiratory dead space, a poor mixing of inspired gas, poor matching of ventilation with perfusion, a decrease of pulmonary diffusing capacity, and a substantial increase in the work of breathing. Ventilatory demand is increased during most physical tasks, but arterial blood homeostasis is surprisingly well maintained when elderly persons undertake vigorous exercise because peak cardiac output declines in parallel with the loss of ventilatory function. However, dyspnea progressively restricts peak effort as one ages. The exercise specialist cannot restore aged or damaged pulmonary tissue but can attempt to reduce the rate of future functional loss by encouraging smoking cessation, avoiding air pollution, and controlling acute infections. Enhanced fitness, stronger skeletal muscles, and better coordination can reduce ventilatory demand. Resisted breathing exercises may also strengthen the chest muscles and allow a mechanically more efficient pattern of breathing.
Master Swimmers: How Are They Different from Younger Elite Swimmers? an Examination of Practice and Performance Patterns
Authors: Weir Patricia L. , Kerr Tracey , Hodges Nicola J. , McKay Sandra M. , Starkes Janet L.
Published: August 2016

Recent work in the area of sport expertise suggests that practice patterns can also play a critical role in maintaining athletic performance. This article examines the contribution of both physiological changes and practice patterns to swimming performances of master-, international-, junior-national-, and varsity-level swimmers. A comparison of the practice patterns of these groups suggests that master athletes spend significantly less time per week training for competition, and their training focus is on endurance, not strength. Younger swimmers train for endurance, strength, speed, and power. The authors suggest that these differences might be partly responsible for age-related performance changes. Performance changes for semilongitudinal and cross-sectional samples are characterized by significant quadratic beta weight, indicating increasing declines in performance starting at around 60 years of age. These data are discussed with respect to the role that practice plays in explaining performance changes with age.
Effect of Proprioceptive Neuromuscular Facilitation Stretch Techniques on Trained and Untrained Older Adults
Authors: Ferber Reed , Gravelle Denise C. , Osternig Louis R.
Published: August 2016

The effects of proprioceptive neuromuscular facilitation (PNF) on joint range of motion (ROM) for older adults are unknown, and few studies have investigated changes in joint ROM associated with age. This study examined PNF stretch techniques' effects on knee-joint ROM in trained (T) and untrained (UT) older adults. Knee-joint ROM was tested in T and UT adults age 45–55 and 65–75 years using 3 PNF stretch techniques: static stretch (SS), contract-relax (CR). and agonist contract-relax (ACR). The 45–55 UT group achieved significantly more ROM than did the 65–75 UT group, suggesting an age-related decline in ROM. The 65–75 T group achieved significantly greater knee-extension ROM than did their UT counterparts, indicating a training-related response to PNF stretch techniques and that lifetime training might counteract age-related declines in joint ROM. The ACR-PNF stretch condition produced 4–6° more ROM than did CR and SS for all groups except the 65–75 UT group, possibly as a result of lack of neuromuscular control or muscle strength.