bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comparison of Methods to Quantify the In-Season Training Load of Professional Soccer Players
Authors: Scott Brendan R. , Lockie Robert G. , Knight Timothy J. , Clark Andrew C. , Janse de Jonge Xanne A.K.
Published: August 2016

Purpose:

To compare various measures of training load (TL) derived from physiological (heart rate [HR]), perceptual (rating of perceived exertion [RPE]), and physical (global positioning system [GPS] and accelerometer) data during in-season field-based training for professional soccer.

Methods:

Fifteen professional male soccer players (age 24.9 ± 5.4 y, body mass 77.6 ± 7.5 kg, height 181.1 ± 6.9 cm) were assessed in-season across 97 individual training sessions. Measures of external TL (total distance [TD], the volume of low-speed activity [LSA; <14.4 km/h], high-speed running [HSR; >14.4 km/h], very high-speed running [VHSR; >19.8 km/h], and player load), HR and session-RPE (sRPE) scores were recorded. Internal TL scores (HR-based and sRPE-based) were calculated, and their relationships with measures of external TL were quantified using Pearson product–moment correlations.

Results:

Physical measures of TD, LSA volume, and player load provided large, significant (r = .71−.84; P < .01) correlations with the HR-based and sRPE-based methods. Volume of HSR and VHSR provided moderate to large, significant (r = .40−.67; P < .01) correlations with measures of internal TL.

Conclusions:

While the volume of HSR and VHSR provided significant relationships with internal TL, physical-performance measures of TD, LSA volume, and player load appear to be more acceptable indicators of external TL, due to the greater magnitude of their correlations with measures of internal TL.
Assessment of Sprint and Change-of-Direction Performance in College Football Players
Authors: Condello Giancarlo , Schultz Kevin , Tessitore Antonio
Published: August 2016

The aim of the current study was to investigate the relationship between straight-sprint and change-of-direction performance. Total sprinting time and split time at 5 m were collected from 44 college football players during a 15-m straight sprint (SS15m) and a 15-m zigzag sprint with two 60° changes of direction (COD15m). Differences in sprinting time between COD15m and SS15m and between COD5m and SS5m were expressed as percentage of decrement at 5 m and 15 m (Δ%5m and Δ%15m). Significant and high correlations emerged between SS15m and COD15m (r = .86, P < .0001), SS5m and SS15m (r = .92, P < .0001), SS5m and COD5m (r = .92, P < .0001), and COD5m and COD15m (r = .71, P < .0001). Δ%5m and Δ%15m showed a range of 1.2–30.0% and 34.9–59.4%, respectively. These results suggested how straight-sprint and change-of-direction performance are similar abilities in college football players, in particular when a smaller angle of the change of direction is considered. Moreover, it seems necessary to have athletes undergo tests that mimic the demands of football game, which is characterized by sprint on short distances and with changes of direction.
A Novel Approach for Lactate Threshold Assessment Based on Rating of Perceived Exertion
Authors: Fabre Nicolas , Mourot Laurent , Zerbini Livio , Pellegrini Barbara , Bortolan Lorenzo , Schena Federico
Published: August 2016

This study tested the hypothesis that the DMAX (for maximal distance) method could be applied to ratings of perceived exertion (RPE), to propose a novel method for individual detection of the lactate threshold (LT) using RPE alone during an incremental test to exhaustion. Twenty-one participants performed an incremental test on a cycle ergometer. At the end of each stage, lactate concentration was measured and the participants estimated RPE using the Borg CR100 scale. The intensity corresponding to the fixed lactate values of 2 or 4 mmol · L−1(2mM and 4mM), the ventilatory threshold (VT), the respiratory-compensation point (RCP), and the instant of equality of pulmonary gas exchange (RER=1.00) were determined. Lactate (DMAX La) and RPE (DMAX RPE) thresholds were determined using the DMAX method. Oxygen uptake (VO2), heart rate, and power output measured at DMAX RPE and at DMAX La were not statistically different. Bland-Altman plots showed small bias and good agreements when DMAX RPE was compared with the DMAX La and RER=1.00 methods (bias = −0.05% and −2% of VO2max, respectively). Conversely, VO2 from the DMAX RPE method was lower than VO2 at 4 mM and at RCP and was higher than VO2 at 2 mM and at VT. VO2 at DMAX RPE was strongly correlated with VO2 at DMAX La (r = .97), at RER=1.00 (r = .97), at 2 mM (r = .85), at 4 mM (r = .93), at VT (r = .95), and at RCP (r = .95). The combination of the DMAX method with the RPE responses permitted precise and individualized estimates of LT using the DMAX method.
The Reliability of a 30-s Sprint Test on the Wattbike Cycle Ergometer
Authors: Driller Matthew W. , Argus Christos K. , Shing Cecilia M.
Published: August 2016

Purpose:

To determine the reliability of a 30-s sprint cycle test on the Wattbike cycle ergometer.

Methods:

Over 3 consecutive weeks, 11 highly trained cyclists (mean ± SD; age 31 ± 6 y, mass 74.6 ± 10.6 kg, height 180.5 ± 8.1cm) completed four 30-s maximal sprints on a Wattbike ergometer after a standardized warmup. The sprint test implemented a “rolling start” that consisted of a 60-s preload (at an intensity of 4.5 W/kg) before the 30-s maximal sprint. Variables determined across the duration of the sprint were peak power (Wpeak), mean power (Wmean), W/kg, mean cadence (rpm), maximum heart rate (n = 10), and postexercise blood lactate.

Results:

The average intraclass correlation coefficients between trials (2v1, 3v2, 4v3, 4v1) were Wpeak .97 (90%CI .94–.99), Wmean .99 (90%CI .97–1.00), W/kg .96 (90%CI .91–.98), mean cadence .96 (90%CI .92–.99), maximum heart rate .99 (90%CI .97–.99), and postexercise blood lactate .94 (90%CI .87–.98). The average typical error of measurement (expressed as a CV% and absolute value between trials—2v1, 3v2, 4v3, 4v1) was Wpeak 4.9%, 52.7 W; Wmean 2.4%, 19.2 W; W/kg 2.3%, 0.18 W/kg; mean cadence 1.4%, 1.6 rpm; maximum heart rate 0.9%, 1.6 beats/min; and postexercise blood lactate 4.6%, 0.48 mmol/L.

Conclusion:

A 30-s sprint test on the Wattbike cycle ergometer is highly reproducible in trained cyclists.
Individualization of Time–Motion Analysis: A Case-Cohort Example
Authors: Lovell Ric , Abt Grant
Published: August 2016

Purpose:

To report the intensity distribution of Premier League soccer players’ external loads during match play, according to recognized physiological thresholds. The authors also present a case in which individualized speed thresholds changed the interpretation of time–motion data.

Method:

Eight outfield players performed an incremental treadmill test to exhaustion to determine the running speeds associated with their ventilatory thresholds. The running speeds were then used to individualize time–motion data collected in 5 competitive fixtures and compared with commonly applied arbitrary speed zones.

Results:

Of the total distance covered, 26%, 57%, and 17% were performed at low, moderate, and high intensity, respectively. Individualized time– motion data identified a 41% difference in the high-intensity distance covered between 2 players of the same positional role, whereas the player-independent approach yielded negligible (5–7%) differences in total and high-speed distances covered.

Conclusions:

The authors recommend that individualized speed thresholds be applied to time–motion-analysis data in synergy with the traditional arbitrary approach.
The Effects of 4 Different Recovery Strategies on Repeat Sprint-Cycling Performance
Authors: Argus Christos K. , Driller Matthew W. , Ebert Tammie R. , Martin David T. , Halson Shona L.
Published: August 2016

Purpose:

To evaluate the effectiveness of different recovery strategies on repeat cycling performance where a short duration between exercise bouts is required.

Methods:

Eleven highly trained cyclists (mean ± SD; age = 31 ± 6 y, mass = 74.6 ± 10.6 kg, height = 180.5 ± 8.1 cm) completed 4 trials each consisting of three 30-s maximal sprints (S1, S2, S3) on a cycle ergometer, separated by 20-min recovery periods. In a counterbalanced, crossover design, each trial involved subjects performing 1 of 4 recovery strategies: compression garments (COMP), electronic muscle stimulation (EMS), humidification therapy (HUM), and a passive control (CON). The sprint tests implemented a 60-s preload (at an intensity of 4.5 W/kg) before a 30-s maximal sprint. Mean power outputs (W) for the 3 sprints, in combination with perceived recovery and blood lactate concentration, were used to examine the effect of each recovery strategy.

Results:

In CON, S2 and S3 were (mean ± SD) –2.1% ± 3.9% and –3.1% ± 4.2% lower than S1, respectively. Compared with CON, COMP resulted in a higher mean power output from S1 to S2 (mean ± 90%CL: 0.8% ± 1.2%; possibly beneficial) and from S1 to S3 (1.2% ± 1.9%; possibly beneficial), while HUM showed a higher mean power output from S1 to S3 (2.2% ± 2.5%; likely beneficial) relative to CON.

Conclusion:

The authors suggest that both COMP and HUM may be effective strategies to enhance recovery between repeated sprint-cycling bouts separated by ~30 min.
An Approach to Estimating Gross Efficiency During High-Intensity Exercise
Authors: de Koning Jos J. , Noordhof Dionne A. , Uitslag Tom P. , Galiart Rianna E , Dodge Christopher , Foster Carl
Published: August 2016

Purpose:

Gross efficiency (GE) is coupling power production to propulsion and is an important performance-determining factor in endurance sports. Measuring GE normally requires measuring VO2 during submaximal exercise. In this study a method is proposed to estimating GE during high-intensity exercise.

Methods:

Nineteen subjects completed a maximal incremental test and 2 GE tests (1 experimental and 1 control test). The GE test consisted of 10 min cycling at 50% peak power output (PPO), 2 min at 25 W, followed by 4 min 100% PPO, 1 min at 25 W, and another 10 min at 50% PPO. GE was determined for the 50%-PPO sections and was, for the second 50%-PPO section, back-extrapolated, using linear regression, to the end of the 100%-PPO bout.

Results:

Back-extrapolation of the GE data resulted in a calculated GE of 15.8% ± 1.7% at the end of the 100%-PPO bout, in contrast to 18.3% ± 1.3% during the final 2 min of the first 10-min 50%-PPO bout.

Conclusion:

Back-extrapolation seems valuable in providing more insight in GE during high-intensity exercise.
A Kinematic Comparison of Single, Double, and Triple Axels
Authors: King Deborah L. , Arnold Allison S. , Smith Sarah L.
Published: August 2016

To be competitive internationally, figure skaters today must perform complex athletic skills such as triple axels. However, few skaters are executing such jumps consistently. In this study, a 3D kinematic analysis of five elite male skaters was undertaken to compare characteristics of single, double, and triple axels and to determine which parameters are most critical to completion of the triple axel. Results indicate that skaters increase their number of revolutions by increasing their rotational velocity, not by increasing their time in the air. The study also shows that skaters' triple axels travel horizontally only 70% as far as their single axels, an observation attributable to skaters' greater skid distances, greater takeoff angles, and consequently lower horizontal velocities in their triple axels. It appears that achieving a high rotational velocity by generating angular momentum at takeoff and by minimizing moment of inertia about the spin axis is a key to completing the triple axel.
Baseball Bat Inertial and Vibrational Characteristics and Discomfort Following Ball–Bat Impacts
Authors: Noble Larry , Walker Hugh
Published: August 2016

This study examined the relationship between selected mechanical characteristics of aluminum baseball bats and sensations on the hands resulting from impacts. Sixteen skilled male Little League baseball players held each of two bats while they were impacted at the following locations by baseballs at speeds of approximately 27 m/s: near barrel end, center of percussion (COP), distal node of the fundamental mode, and 4 in. toward the hands from the COP. Results of a questionnaire regarding annoyance and discomfort were correlated with selected bat characteristics and vibrational characteristics associated with each impact condition. Results indicated that perceptions of annoyance and discomfort were related to the level of excitation of the fundamental mode and first overtone mode and that annoyance and discomfort were less with impacts on the COP and fundamental vibrational node.
Twisting Techniques Used in Dismounts from the Rings
Authors: Yeadon Maurice R.
Published: August 2016

At the 1992 Olympic Games six full twisting double somersault dismounts were recorded with two video cameras during the rings individual apparatus finals in the men's Artistic Gymnastics competition. Angles describing body configuration were determined from video data and were input, together with initial orientation angle values and angular momentum components, into a computer simulation model of aerial movement. Mean absolute deviations between simulation and video after the completion of one half twist were 0.01 rev for somersault, 2.8° for tilt, and 0.08 rev for twist. When the estimate of the initial tilt angle was adjusted by up to 1° these deviations fell to 1.6° for tilt and 0.02 rev for twist. All 6 competitors produced the majority of the tilt using aerial techniques that were predominantly asymmetrical movements of the arms. Contributions to the subsequent removal of tilt were determined using reverse simulations, and again arm movements were the main contributors.
A Kinematic Profile of the Approach Run of Novice Long Jumpers
Authors: Berg William P. , Greer Nancy L.
Published: August 2016

This study determined the kinematics of the final 11 steps of the long jump approach (LJA) for 19 novice long jumpers. Associations between takeoff accuracy and jump performance were identified, and comparisons of LJA kinematics were made with previous investigations of horizontal jumps performed by expert long jumpers. Results indicated that absolute takeoff error was not an important determinant of jump distance for the novice long jumpers. Additionally, novice jumpers differed from expert jumpers in terms of the relationships among specific variables. The results suggest that kinematic variables that appear to be causally related to jump performance in experts may not piay a similar role in the performance of novices. Hypotheses for these differences were offered. Differences between the LJAs of novice and expert long jumpers warrant further investigation, so that their origins can be determined and used to develop effective training regimes.
Pressure Distributions on the Plantar Surface of the Foot during the Javelin Throw
Authors: Bartlett Roger , Müller Erich , Raschner Christian , Lindinger Stefan , Jordan Caroline
Published: August 2016

The aim of this study was to compare the plantar pressures and forces recorded from both feet of two groups of javelin throwers of different performance levels, in order to investigate differences between skill levels. The study was carried out using an EMED insole system on a Tartan javelin runway at the University of Innsbruck, Austria. Most of the differences (at p < .01) between the two groups were found in the two foot contacts during the delivery stride. Higher maximum total forces (forces on the whole foot) and maximum pressures were recorded for the more skilled or club throwers during the right foot contact at the beginning of this stride. For the left foot landing before release, the club throwers exhibited higher overall maximum forces and overall pressures (the largest forces and pressures recorded on any of the different foot regions) than the novices. The differences between the groups in the medial forefoot region contributed significantly to this result.
Rearfoot Motion and Pressure Distribution Patterns during Running in Shoes with Varus and Valgus Wedges
Authors: Milani Thomas L. , Schnabel Gerrit , Hennig Ewald M.
Published: August 2016

The purpose of this study was to investigate the influence of 8° varus and vaigus shoe modifications on the foot mechanics in overground running. Twenty male subjects performed eight rearfoot running trials in three shoe conditions. Ground reaction forces, tibial accelerations, rearfoot motion, and in-shoe pressure distribution data were collected simultaneously. Between footwear conditions, force and acceleration parameters were found to be significantly different. Compared to the neutral shoe, maximum pronation and pronation velocity were reduced for the varus and increased for the vaigus shoes. Higher lateral rearfoot loads and an increased contribution of the first ray in the forefoot could be evaluated for the vaigus shoe. In contrast, a larger contribution of the medial midfoot and the fifth metatarsal head was observed for the varus shoe. The relative load analysis from the pressure distribution measurements provided additional information about the behavior of the foot in response to major changes in shoe construction.
Techniques Used by Olympic Ski Jumpers in the Transition from Takeoff to Early Flight
Authors: Arndt Anton , Brüggemann Gert-Peter , Virmavirta Mikko , Komi Paavo
Published: August 2016

This study was concerned with identifying important flight characteristics of the ski jump at the end of the early flight phase and describing how these characteristics developed from the run-in through the takeoff and during the early flight phase. The K90 individual competition of the 1994 Olympic Winter Games was analyzed. The 2-D data (takeoff) were collected by a high-speed video camera, and the 3-D analysis (early flight) used an algorithm whereby two cameras followed the jumpers through the early flight phase. Center of mass (CM) velocities at takeoff and after early flight and CM heights at these positions had no significant linear correlations with total distance. Only small differences in these parameters were distinguished between better and poorer performers. Significant differences between jumpers were identified in angular parameters at takeoff and in early flight. A combination of five defined flight angles yielded an R2 value of .84. It was found that the complex movement sequences involved in ski jumping were therefore more important in their contributions to optimal flight position than the ballistic properties of the ski jumper reduced to a single point model.
A New Bicycle Pedal Design for On-Road Measurements of Cycling Forces
Authors: Álvarez Gorka , Vinyolas Jordi
Published: August 2016

A pedal is presented that was designed specifically for the evaluation of cycling technique of different cyclists in real conditions. Most of the instrumented force pedals referred to in research literature have been designed for laboratory use, where pedal weight and dimension have not been considered critical characteristics. By means of this new instrumented force pedal, which is externally identical to one of the most popular clipless pedals, cycling forces under real conditions are measured. The interest in this pedal lies in the fact that it can be used in road trials like the sprint or climb, where tridimensional movements must be considered. Some measurements obtained in hill climb cycling, such as maximum normal force and force distribution during crank revolution, are also presented and discussed.
Kinematic and Kinetic Comparison between Baseball Pitching and Football Passing
Authors: Fleisig Glenn S. , Escamilla Rafael F. , Andrews James R. , Matsuo Tomoyuki , Satterwhite Yvonne , Barrentine Steve W.
Published: August 2016

Kinematic and kinetic aspects of baseball pitching and football passing were compared. Twenty-six high school and collegiate pitchers and 26 high school and collegiate quarterbacks were analyzed using three-dimensional high-speed motion analysis. Although maximum shoulder external rotation occurred earlier for quarterbacks, maximum angular velocity of pelvis rotation, upper torso rotation, elbow extension, and shoulder internal rotation occurred earlier and achieved greater magnitude for pitchers. Quarterbacks had shorter strides and stood more erect at ball release. During arm cocking, quarterbacks demonstrated greater elbow flexion and shoulder horizontal adduction. To decelerate the arm, pitchers generated greater compressive force at the elbow and greater compressive force and adduction torque at the shoulder. These results may help explain differences in performance and injury rates between the two sports.
Muscle Activity Patterns of Elite Downhill Ski Racers during Landing
Authors: Schaff Peter , Nordsletten Lars , Aune Arne Kristian
Published: August 2016

The purpose of this study was to examine motion and muscle activity in downhill skiing in order to estimate muscular involvement during the landing phase and its potential effect on ACL injury. Specially developed 8-channel portable electromyo-graphy registration was conducted during three jumps on the Russi jump of the 1994 Olympic downhill slope, and six control jumps were carried out in the laboratory. The results reveal that the skier adapts to the expected loading of the knee, possibly by using a learned motor control pattern. It is still not clear, however, how important muscular adaptation to expected forces is. The complex functional EMG pattern that skiers use while landing indicates that ACL rupture caused during a backward fall in downhill skiing might be due to a combination of the boot-top-induced anterior shear, the force generated in the ACL by forceful knee hyperflexion supported by the high bending moment generated by a stiff spoiler, and the possible absence of a significant protecting hamstrings force during maximum loading.
The Effect of Rearfoot Motion on Attenuation of the Impulse Wave at Impact during Running
Authors: Yingling Vanessa R. , Yack H. John , White Scott C.
Published: August 2016

This study investigated whether rearfoot motion at heel contact during running attenuates the magnitude of the impact force traveling through the body. Fifteen subjects completed running trials for two conditions:(a) running on a treadmill at a self-selected speed and a cadence of 160 steps/min and (b) running at the same speed and cadence but with rearfoot motion limited by a medial wedge inserted into the subject's shoe. A pairedttest was used to test for differences between conditions in the peak accelerations of each accelerometer and the time to peak of the tibia acceleration. The predominant impact frequency and amplitude of the frequency peak were also tested for significant differences. No significant difference was found in the variables compared between the two conditions. The results demonstrated that restriction of rearfoot motion using a medial wedge during the initial 15% of the stance phase has no effect on the characteristics of the impulse wave at the tibia.
Functional Biomechanical Analysis of the Pilates-Based Reformer during Demi-Plié Movements
Authors: Self Brian P. , Bagley Anita M. , Triplett Teresa L. , Paulos Lonnie E.
Published: August 2016

The Pilates-based reformer is used by dancers for training and for injury rehabilitation. Knee kinematics and applied forces during demi-plié in fifth and in first positions were analyzed while dancers performed the motions (a) standing, (b) on the reformer equipped with two springs, and (c) on the reformer equipped with four springs. The highest forces, normalized to body weight, were obtained for the standing demi-plié, while the largest knee flexion angles occurred on the reformer with four springs. Greater range of motion was achieved in first position than in fifth, and females exhibited greater extension and higher normalized forces than males, It was also noted that force/knee angle relationships for the standing demi-plié and for the reformer tests were quite different. Reformer forces were totally dependent on the knee angle, whereas the forces during the standing demi-plié depended on the acceleration of the dancer's center of gravity.
Biomechanical Testing of Materials Used in the Construction of Playing Casts
Authors: Bahamonde Rafael E. , Malone Kathy
Published: August 2016

The purpose of this study was to test the mechanical properties of popular playing cast materials and their abilities to absorb the force produced by an impact. A Shore A2 durometer was used to test the hardness of four types of materials: RTV11, Delta-Lite®, QuickCast™, and Scotchcast™Soft Cast. Force absorption characteristics of the materials were analyzed using a drop test. The rigidity (stiffness) of the materials was measured using modulus of elasticity procedures. ANOVA techniques were used to analyze the differences between group means for hardness, peak force, percentage of force absorbed, modulus of elasticity, and compressive stress. There were significant differences in the hardness of the materials. The QuickCast™ and the RTV11 were able to absorb a large percentage of the impact force and had the lowest compressive stress values. In the modulus of elasticity test, QuickCast™ proved to be the most rigid of the materials. The best values for the performance coefficient were obtained by QuickCast™ and RTV11.
A Technique for Measuring Clothed Range of Joint Motion
Authors: Maulucci Ruth A. , Eckhouse Richard H.
Published: August 2016

The study of range of joint motion is of theoretical and practical interest to basic research, workspace design, rehabilitation, and mathematical models. Nude range of motion has been extensively explored, whereas range of motion under clothed conditions, although equally important in applications, has received less attention. A project was designed to investigate modern instrumentation and methodologies for examining clothed range of joint motion. An empirical study was conducted using three distinct techniques simultaneously, involving 6 subjects, two military ensembles, and 46 planar motions. The results of the study showed one of the techniques, a computerized six-degree-of-freedom electromagnetic tracker, to be superior for joint motion applications under clothed conditions. Customized physical modifications and software were implemented to adapt the device for physiological applications, and algorithms were created for extracting joint motion information. Standardized procedures for performance strategies were defined. Recommendations were also given for the use of the other two techniques in applications having different requirements.
Lower Limb Cycling Mechanics in Subjects with Unilateral Cerebrovascular Accidents
Authors: Perell Karen L. , Gregor Robert J. , Scremin A.M. Erika
Published: August 2016

Biomechanical analysis of the generalized muscle moment and power patterns involved in cycling provides information regarding coordination within each limb. The purpose of this study was to compare individual joint kinetics, bilaterally, in subjects who had experienced cerebrovascular accidents (CVAs). Two-dimensional cinematography and force pedal data in a linked-segment model were used to study 8 ambulatory subjects while they rode a recumbent bicycle. The involved lower limb was defined as the lower limb with the greatest deficits, whereas the contralateral lower limb was defined as the lower limb opposite the involved lower limb and ipsilateral to the lesion site. The contralateral lower limbs of subjects with CVAs demonstrated patterns similar to those reported for nondisabled cyclists on an upright bicycle except for a bimodal hip power generation pattern that was possibly due to compensation for a lack of involved lower limb power generation. There were two critical findings of this study: Single-joint power generation patterns during the power phase indicated that either the hip or the knee, but not both joints, generated power in the involved lower limb, and asymmetrical differences between lower limbs appeared significant at the ankle alone.
Three-Dimensional Analysis of Handspring with Full Turn Vault: Deterministic Model, Coaches' Beliefs, and Judges' Scores
Authors: Takei Yoshiaki
Published: August 2016

The purpose of the study was to identify mechanical variables that govern successful performance of the handspring with full turn vault. Subjects were 67 male gymnasts from 25 countries performing the vault during the 1992 Olympic Games. The vaults were filmed by two 16-mm Locam II DC cameras operating at 100 Hz. Approximately 80 frames per subject were digitized for each camera view. Direct linear transformation (DLT) was used to calculate the 3-D coordinates of the digitized body points. The method of Hay and Reid (1988) was used to develop a theoretical model to identify the mechanical variables that determine linear and angular motions of the vault. Significant correlations (p < .005) indicated that the following were important determinants for success: large horizontal velocity, large horizontal kinetic energy term, and overall translational kinetic energy term at takeoff from the board; short duration, small vertical displacement of the center of gravity (CG), and small somersaulting angular distance of preflight; large vertical velocity and large vertical kinetic energy term at takeoff from the horse; and large "amplitude of postflight," that is, large horizontal and vertical displacements of CG and long duration of flight; great height of CG during the second quarter-tum in postflight; and small point deduction for landing.
Incidence and Severity of Head Impact during Freestyle Aerial Ski Jumping
Authors: Mecham Matthew D. , Greenwald Richard M. , Macintyre James G. , Johnson Stephen C.
Published: August 2016

A field study was performed using freestyle aerial ski jumpers to determine the incidence of head impact (slapback) and to record head acceleration data during slapback episodes for the 1994–1995 and 1995–1996 winter seasons. A total of 382 slapbacks were recorded from 2,352 jumps for an observed slapback incidence of 16.2%. Head acceleration data were recorded for 5 slapback events. Maximum head acceleration magnitudes for the 5 impacts ranged from 27 to 92 gs and impact durations ranged from 12 to 96 μsec. Standard severity indices including the Gadd Severity Index and Head Injury Criteria were calculated from the resultant acceleration signal and ranged from 57 to 223, and 21 to 159, respectively, which are considered low in terms of life threatening injury levels.
Exploring Unique Applications of Kinetic Analyses to Movement in Older Adults
Authors: Wolf Steven L. , Gregor Robert J.
Published: August 2016

During the past decade, considerable effort has been directed toward evaluating kinetic responses among older individuals particularly with the intent of better understanding events predictive of or leading to falling behavior. Within this context, neither provision of visual feedback of kinetic responses to angular perturbations to shape postural responses nor the assessment of postural responses to anticipated or unexpected movements following unique exercise interventions, including Tai Chi, has been explored. Generally, the magnitude of vertical loading responses does not appear amenable to conditioning, but an analysis of kinetic changes observed during movements holds more potential as a correlate to the delayed onset of falls among older Tai Chi practitioners.
Longer Integration Intervals Reduce Variability and Improve Reliability of EMG Derived from Maximal Isometric Exertions
Authors: Vint Peter F. , Hinrichs Richard N.
Published: August 2016

Isometric knee extension force and average integrated EMG of the vastus lateralis muscle were obtained from 27 healthy subjects using a maximum effort, ramp and hold protocol. In each of the 125 total trials mat were included in the analysis, a 2-s plateau region was extracted and divided into two adjacent 1000-ms bins. Variability and reliability of bin-to-bin measurements of force and EMG were then evaluated across 14 different integration intervals ranging from 10 to 1000 ms. Statistical analyses of bin-to-bin variability measures demonstrated that integration intervals of 250 ms and longer significantly reduced variability and improved reliability of average integrated EMG values during maximum effort isometric exertions. Bin-to-bin EMG reliability increased from .728 at 10 ms to .991 at 1000 ms. Force parameters appeared less sensitive to changes in length of the integration interval. It was suggested that longer intervals might also improve the validity of the EMG-force relationship during maximum effort isometric exertions by reducing problems associated with electromechanical delay.
A Three-Dimensional Biomechanical Analysis of the Cat Ankle Joint Complex: I. Active and Passive Postural Mechanics
Authors: Lawrence John H. , Nichols T. Richard
Published: August 2016

Muscle actions are often defined with respect to a single anatomical reference plane based on a “predominant” functional activity. Yet animals must control posture and movement within a three-dimensional (3-D) environment, exerting control over more than one reference plane when responding to a 3-D array of perturbing forces. Consequently, enhanced knowledge concerning the 3-D torque capabilities of certain appendicular muscles might provide for greater understanding of the biomechanical basis for motor control. We propose that the cat postural control mechanism utilizes the inherent 3-D mechanical actions of ankle flexors and extensors to maintain extra-saggital joint stiffness. We used a 6 degree-of-freedom force-moment sensor to assess the effect of ankle joint orientation on the 3-D nature of isometric joint torques evoked by electrical stimulation of muscles crossing the AJC in the deeply anesthetized cat. An orthogonal axis system was established at the designated ankle rotation center, such that pitch (defining flexion-extension), yaw (abduction-adduction), and roll (inversion-eversion) axis torques were calculated. Experimental results show that the classical cat ankle flexor and extensors evoke large extra-sagittal torques as well. Also, the hind limb levering system stabilizes the AJC against large yaw and roll rotations away from the control position.
Components of the End-Effector Jerk during Voluntary Arm Movements
Authors: Laczko Jozsef , Jaric Slobodan , Tihanyi Jozsef , Zatsiorsky Vladimir M. , Latash Mark L.
Published: August 2016

Jerk (time derivative of acceleration) of the endpoint of a multi-joint kinematic chain can be represented as the sum of terms related to jerks, accelerations, and velocities in individual joints. We investigated the relative contribution of these terms during simulations of planar movement of a 3-segment kinematic chain and also during unconstrained movements at different velocities, over different amplitudes, and with different intentionally changed curvature. Our results demonstrate that the term related to individual joint jerks dominates in the total endpoint jerk. This domination was particularly strong during voluntary movements and was not as striking during the simulations based on 5th-order polynomial functions for individual joint trajectories. Thus, the minimum-jerk criterion for multi-joint movements can be well approximated by minimization of the jerk-related terms for individual joints. The decomposition of endpoint jerk into its terms shows potential limitations of the commonly used 5th-order polynomial modeling for describing voluntary multi-joint movements.
Experimental Vertical Jump Model Used to Evaluate the Pivot Location in Klap Speed Skates
Authors: Allinger Todd L. , Motl Robert W.
Published: August 2016

This study used a vertical jump model to simulate the push-off phase for a skater using klap speed skates and evaluated die effects of pivot location and shoe base flexion on energy production. Boards of different lengths and one board with a hinge under the metatarsal heads were attached to the running shoes of volunteers. Six skaters performed 3 maximal effort vertical jumps across 5 different base conditions: running shoe, board that hinged under metatarsal heads, and rigid boards that pivoted with the ground al -25 mm (typical pivot location for klapskales), 0 mm, and +25 mm from the toes. There were no significant differences in total energy at take-off among the 3 rigid base conditions, but there were differences in potential and kinetic energy production. The total and kinetic energy produced at take-off was 9% greater in the hinged base condition than the corresponding rigid base condition. If differences in energy measures from the vertical jump reflect those for skating, a hinged boot base could increase skating speeds by about 3% over the current klap-skales, which have a rigid boot base.
Lower Extremity Mechanics in Runners with a Converted Forefoot Strike Pattern
Authors: Williams Dorsey S. , McClay Irene S. , Manal Kurt T.
Published: August 2016

Runners are sometimes advised to alter their strike pattern as a means of increasing performance or in response to injury. The purpose of this study was to compare lower extremity mechanics of rearfoot strikers (RFS), who were instructed to run with a forefoot strike pattern (CFFS) to those of a preferred forefoot striker (FFS). Three-dimensional mechanics of 9 FFS and 9 CFFS were evaluated. Peak values for most kinematic and kinetic variables and all patterns of movement were not found to be statistically different between CFFS and FFS. Only peak vertical ground reaction force and peak ankle plantarflexion moment were found to be significantly lower (p ≤ .05) in the CFFS group. This suggests that RFS are able to assume a FFS pattern with very little practice that is very similar to that of a preferred FFS. The impact of changing one's strike pattern on injury risk and running performance needs further study.
A Comparative Analysis of the Center of Gravity and Center of Pressure Trajectory Path Lengths in Standing Posture: An Estimation of Active Stiffness
Authors: Caron Olivier , Gélat Thierry , Rougier Patrice , Blanchi Jean-Pierre
Published: August 2016

The center of foot pressure (CP) motions, representing the net neuromuscular control, was compared to the center of gravity (CG) motions, representing the net performance. The comparison focused on the trajectory path length parameter along the mediolateral and antero-posterior axes because these two variables depend on amplitude versus frequency relationship. This relationship was used to evaluate the CG motions based on the CP motions. Seven subjects stood still on a force plate with eyes open and eyes closed. The results showed that the ratio of (CP – CG)/CP trajectory path length was personal for each subject. These results suggest different levels of passive (ligaments, elastic properties) and active (reflex activity) stiffness. For some subjects, this ratio was significantly lower for the eyes open condition than for the eyes closed condition, indicating a decrease of the active stiffness for the eyes open condition. Therefore, a CG – CP comparative analysis appeared helpful in understanding the control of balance and necessary to quantify the subjects’ net performance.
An Anatomical Database Providing Three-Dimensional Geometric Representation of Lower Limb Structures
Authors: Barr Alan , Hawkins David
Published: August 2016

An anatomical database was constructed containing three-dimensional geometric representations of the structures comprising the lower extremity. The database was constructed by digitizing 100 high-resolution digital photographic images supplied from the National Library of Medicine’s Visual Human Male (VHM) project. These images were taken of sequential transverse cross-sectional slices of the leg. Slices were located 1 cm apart between a location approximately 3 mm below the superior aspect of the ilium and approximately 2 mm below the distal end of the fibula. Image Tool Software (v. 2.0) was used to manually digitize the perimeters of muscles, tendons, and bones of the pelvis, thigh, and shank from the right leg of the VHM. Additionally, the perimeter of the leg and the inner aspect of the superficial fat layer were digitized. The pelvis was digitized as a hemi-pelvis. Tissue perimeters were characterized using between 10 and 151 nodes within each slice; the number of nodes varied depending on the tissue’s size. Transverse cross-sectional slice number, structure identification, node number, and the two-dimensional coordinates of each node were stored in a data file. The information contained in this file is unique and provides a database that researchers can use to investigate questions related to tissue anatomy and movement mechanics that cannot be considered using existing musculoskeletal data sets.
An Insight into the Importance of Wrist Torque in Driving the Golfball: A Simulation Study
Authors: Sprigings Eric J. , Neal Robert J.
Published: August 2016

The purpose of this study was to examine whether, in theory, the clubhead speed at impact could be increased by an optimally timed wrist torque, without jeopardizing the desired club position at impact. A 2-D, three-segment model comprising torso, left arm, and golfclub was used to model the downward phase of the golf swing. Torque generators that adhered to the activation and force-velocity properties of muscle were inserted at the proximal end of each segment. Separate simulations were performed, with the wrist joint generator enabled then disabled. The results from these simulations showed that significant gains in clubhead speed (≈9 %) could be achieved if an active wrist torque was applied to the club during the latter stages of the downswing. For a swing that produced a clubhead speed of 44 m/s (≈99 mph), the optimal timing for the activation of wrist torque occurred when the arm segment was approximately 30° below a horizontal line through the shoulder joint. The optimal activation time for the joint generators was very much dependant on the shape of the torque profiles. The optimization process confirmed that maximum clubhead speed was achieved when the torque generators commenced in sequential order from proximal to distal.
Identification of Release Conditions and Aerodynamic Forces in Pitched-Baseball Trajectories
Authors: Alaways LeRoy W. , Mish Sean P. , Hubbard Mont
Published: August 2016

Pitched-baseball trajectories were measured in three dimensions during competitions at the 1996 Summer Olympic games using two high-speed video cameras and standard DLT techniques. A dynamic model of baseball flight including aerodynamic drag and Magnus lift forces was used to simulate trajectories. This simulation together with the measured trajectory position data constituted the components of an estimation scheme to determine 8 of the 9 release conditions (3 components each of velocity, position, and angular velocity) as well as the mean drag coefficient CD and terminal conditions at home plate. The average pitch loses 5% of its initial velocity during flight. The dependence of estimated drag coefficient on Reynolds number hints at the possibility of the drag crisis occurring in pitched baseballs. Such data may be used to quantify a pitcher’s performance (including fastball speed and amount of curve-ball break) and its improvement or degradation over time. It may also be used to understand the effects of release parameters on baseball trajectories.
Quadriceps Activation during Knee Extension Exercises in Patients with ACL Pathologies
Authors: Suter Esther , Herzog Walter , Bray Robert
Published: August 2016

This study assessed muscle inhibition in patients with chronic anterior cruciate ligament (ACL) deficiency or ACL reconstruction. A series of protocols were tested for their effectiveness in increasing activity of the individual knee extensor muscles and decreasing muscle inhibition of the whole quadriceps group. Quadriceps muscle inhibition was measured by superimposing an electrical twitch onto the quadriceps muscle during a maximal voluntary knee extension. The level of activation of the individual knee extensor and knee flexor muscles was assessed via electromyography (EMG). Patients with ACL pathologies showed strength deficits and muscle inhibition in the knee extensors of the involved leg and the contralateral leg. Muscle inhibition was statistically significantly greater in ACL-deficient patients compared to ACL-reconstructed patients. When a knee extension was performed in combination with a hip extension, there was a significant increase, p < 0.05, in activation of the vastus medialis and vastus lateralis muscles compared to isolated knee extension. The use of an anti-shear device, designed to help stabilize the ACL-deficient knee, resulted in increased inhibition in the quadriceps muscle. Furthermore, a relatively more complete activation of the vasti compared to the rectus femoris was achieved during a fatiguing isometric contraction. Based on the results of this study, it is concluded that performing knee extension in combination with hip extension, or performing fatiguing knee extensor contractions, may be more effective in fully activating the vasti muscles than an isolated knee extensor contraction. Training interventions are needed to establish whether these exercise protocols are more effective than traditional rehabilitation approaches in decreasing muscle inhibition and achieving better functional recovery, including equal muscle strength in the injured and the contralateral leg.
Does Running on a Cambered Road Predispose a Runner to Injury?
Authors: O'Connor Kristian M. , Hamill Joseph
Published: August 2016

Roads are generally designed with a camber to facilitate drainage. Running on a cambered road has been suggested as a potential cause of injury. Two possible mechanisms are mediolateral control and impact shock. The purpose of this study was to investigate the effect of a cambered surface on rearfoot motion and impact shock. Twelve runners ran at 3.83 m/s on both a flat and a cambered surface with the left side raised for all of them. Selected rearfoot kinematic and tibial acceleration measures were evaluated using a 2 × 2 repeated-measures ANOVA. The touchdown angle was less supinated on the left (high) side than on the right (low) side on the cambered surface. Maximum pronation was greater on the left (high) high side than on the right (low) side, as was total rearfoot motion. Maximum velocity of pronation was greater under the left (high) limb than under the right (low) limb while running on the cambered road. Time to maximum pronation did not differ, nor were there differences in peak acceleration or time to peak acceleration. The results of this study suggest that running on a cambered road caused changes in rearfoot motion kinematics that may predispose an individual to injury. Also, since the impact shock did not change with changes in rearfoot motion, perhaps the role of pronation on shock attenuation should be reexamined.