bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological, Anthropometric, and Performance Characteristics of Rugby Sevens Players
Authors: Higham Dean G. , Pyne David B. , Anson Judith M. , Eddy Anthony
Published: August 2016

Although the characteristics of 15-a-side rugby union players have been well defined, there is little information on rugby sevens players.

Purpose:

The authors profiled the anthropometric, physiological, and performance qualities of elite-level rugby sevens players and quantified relationships between these characteristics.

Methods:

Eighteen male international rugby sevens players undertook anthropometric (body mass, height, sum of 7 skinfolds, lean-mass index), acceleration and speed (40-m sprint), muscle-power (vertical jump), repeatedsprint- ability (6 × 30-m sprint), and endurance (Yo-Yo Intermittent Recovery test and treadmill VO2max) testing. Associations between measurements were assessed by correlation analysis.

Results:

Rugby sevens players had anthropometric characteristics (body mass 89.7 ± 7.6 kg, height 1.83 ± 0.06 m, sum of 7 skinfolds 52.2 ± 11.5 mm; mean ± SD) similar to those of backs in international 15-player rugby union. Acceleration and speed (40-m sprint 5.11 ± 0.15 s), muscle-power (vertical jump 66 ± 7 cm), and endurance (VO2max 53.8 ± 3.4 mL · kg−1 · min−1 ) qualities were similar to, or better than, those of professional 15-a-side players. Coefficients of variation ranged from 2.5% to 22%. Relative VO2max was largely correlated with Yo-Yo distance (r = .60, .21−.82; 90% confidence interval) and moderately correlated with 40-m sprint time (r = −.46, −.75 to −.02) and repeated-sprint ability (r = −.38, −.72 to .09).

Conclusions:

International rugby sevens players require highly developed speed, power, and endurance to tolerate the demands of competition. The small between-athletes variability of characteristics in rugby sevens players highlights the need for relatively uniform physical and performance standards in contrast with 15-a-side players.
Consistency of Pacing and Metabolic Responses During 2000-m Rowing Ergometry
Authors: Gee Thomas I. , French Duncan N. , Gibbon Karl C. , Thompson Kevin G.
Published: August 2016

Purpose:

This study investigated the pacing strategy adopted and the consistency of performance and related physiological parameters across three 2000-m rowing-ergometer tests.

Methods:

Fourteen male well-trained rowers took part in the study. Each participant performed three 2000-m rowing-ergometer tests interspersed by 3–7 d. Throughout the trials, respiratory exchange and heart rate were recorded and power output and stroke rate were analyzed over each 500 m of the test. At the completion of the trial, assessments of blood lactate and rating of perceived exertion were measured.

Results:

Ergometer performance was unchanged across the 3 trials; however, pacing strategy changed from trial 1, which featured a higher starting power output and more progressive decrease in power, to trials 2 and 3, which were characterized by a more conservative start and an end spurt with increased power output during the final 500 m. Mean typical error (TE; %) across the three 2000-m trials was 2.4%, and variability was low to moderate for all assessed physiological variables (TE range = 1.4−5.1%) with the exception of peak lactate (TE = 11.5%).

Conclusions:

Performance and physiological responses during 2000-m rowing ergometry were found to be consistent over 3 trials. The variations observed in pacing strategy between trial 1 and trials 2 and 3 suggest that a habituation trial is required before an intervention study and that participants move from a positive to a reverse-J-shaped strategy, which may partly explain conflicting reports in the pacing strategy exhibited during 2000-m rowing-ergometer trials.
Optimal Race Strategy for a 200-m Flying Sprint in a Human-Powered Vehicle: A Case Study of a World-Record Attempt
Authors: de Koning Jos J. , van der Zweep Cees-Jan , Cornelissen Jesper , Kuiper Bouke
Published: August 2016

Optimal pacing strategy was determined for breaking the world speed record on a human-powered vehicle (HPV) using an energy-flow model in which the rider’s physical capacities, the vehicle’s properties, and the environmental conditions were included. Power data from world-record attempts were compared with data from the model, and race protocols were adjusted to the results from the model. HPV performance can be improved by using an energy-flow model for optimizing race strategy. A biphased in-run followed by a sprint gave best results.
The Effects of BungeeSkate Training on Measures of On-Ice Acceleration and Speed
Authors: Janot Jeffrey M. , Auner Kelly A. , Emberts Talisa M. , Kaatz Robert M. , Matteson Kaelyn M. , Muller Emily A. , Cook Mitchell
Published: August 2016

Purpose:

Previous research has stated that dryland sled pulling trains first-step quickness in hockey players. Further research has demonstrated that off-ice horizontal training (sled pull, parachute, etc) relates well to on-ice acceleration and speed. However, there is limited literature pertaining to on-ice resistance training that aims to enhance speed and acceleration in hockey players. The purpose of the current study was to determine if on-ice BungeeSkate training would improve on-ice speed and acceleration in youth hockey players.

Methods:

Twenty-three Peewee and Bantam hockey players (age 11–14) were recruited, with 20 participants completing the study. Pretesting and posttesting consisted of an on-ice 44.8-m speed test, a 6.1-m acceleration test, and a 15.2-m full-speed test. The training protocol consisted of 8 sessions of 5 BungeeSkate training exercises per session, 2 times per week for a 4-wk period.

Results:

The results of this study showed that speed and top speed were significantly increased (P < .05) by 4.2% and 4.3%, respectively. Acceleration was also slightly improved but not significantly.

Conclusions:

A 4-wk BungeeSkate training intervention can improve acceleration and speed in youth hockey players. This training method could be a valid adjunct to existing strategies to improve skill development in hockey and is shown to improve speed and acceleration in relatively short training sessions. This may be most advantageous for hockey coaches and players who are looking to maximize training benefits with limited ice time.
Aggravation of Pulmonary Diffusing Capacity in Highly Trained Athletes by 6 Weeks of Low-Volume, Low-Intensity Training
Authors: Galy Olivier , Maimoun Laurent , Coste Olivier , Manetta Jérôme , Boussana Alain , Préfaut Christian , Hue Olivier
Published: August 2016

Purpose:

Postexercise alveolar-capillary membrane-diffusing capacity (DLco) often decreases in highly trained endurance athletes and seems linked to their training status. To test the hypothesis that training status influences postexercise DLco, 13 male and 2 female triathletes (20.2 ± 4.4 y old, 175.2 ± 6.7 cm tall; weight in a range of 66.6 ± 7.4 kg to 67.4 ± 7.8 kg during the 1-y study) were randomized into experimental (n = 7) and control (n = 8) groups and performed VO2max cycle tests and simulated cycle-run successions (CR) of 30 min + 20 min after 3 periods in the competitive season.

Methods:

Both groups were tested before (pre- HTP) and after a 30-wk high-training period (HTP) with high training volume, intensity, and frequency. The experimental group was then also tested after a 6-wk low-training period (LTP) with low training volume, intensity, and frequency, while the control group continued training according to the HTP schedule for these 6 wk. Ventilatory data were collected continuously. DLco testing was performed before and 30, 60, and 120 min after the CR trials.

Results:

Whatever the period or group, DLco was significantly decreased 30 min after CR, with a significantly greater decrease in the experimental group than the control group in LTP (−15.7% and –9.3% of DLco, respectively).

Conclusions:

Six weeks of low training volume and intensity were sufficient to reverse the effects of high training volume and intensity on the alveolar-capillary membrane after a CR succession in competitive triathletes.
A Case Study of an Iron-Deficient Female Olympic 1500-m Runner
Authors: Pedlar Charles R. , Whyte Gregory P. , Burden Richard , Moore Brian , Horgan Gill , Pollock Noel
Published: August 2016

This case study examines the impact of low serum ferritin (sFe) on physiological assessment measures and performance in a young female 1500-m runner undertaking approximately 95–130 km/wk training. The study spans 4 race seasons and an Olympic Games. During this period, 25 venous blood samples were analyzed for sFe and hemoglobin (Hb); running economy, VO2max, and lactate threshold were measured on 6 occasions separated by 8–10 mo. Training was carefully monitored including 65 monitored treadmill training runs (targeting an intensity associated with the onset of blood lactate accumulation) using blood lactate and heart rate. Performances at competitive track events were recorded. All data were compared longitudinally. Mean sFe was 24.5 ± 7.6 μg/L (range 10–47), appearing to be in gradual decline with the exception of 2 data points (37 and 47 μg/L) after parenteral iron injections before championships, when the lowest values tended to occur, coinciding with peak training volumes. Each season, 1500-m performance improved, from 4:12.8 in year 1 to 4:03.5 in year 4. VO2max (69.8 ± 2.0 mL · kg−1 · min−1) and running economy (%VO2max at a fixed speed of 16 km/h; max 87.8%, min 80.3%) were stable across time and lactate threshold improved (from 14 to 15.5 km/h). Evidence of anemia (Hb <12 g/dL) was absent. These unique data demonstrate that in 1 endurance athlete, performance can continue to improve despite an apparent iron deficiency. Raising training volume may have caused increased iron utilization; however, the effect of this on performance is unknown. Iron injections were effective in raising sFe in the short term but did not appear to affect the long-term pattern.
USA Hockey’s American Development Model: Changing the Coaching and Player Development Paradigm
Authors: Martel Ken
Published: August 2016

Despite significant advances in the development and performance of United States-born hockey players since the 1970s, room for improvement remains, especially when one compares the U.S. to its top international competition, much of which succeeds at the Olympic and World Championship level with dramatically smaller pools of talent from which to assemble its elite teams. USA Hockey sought to address this performance discrepancy and fulfill the full potential of American hockey through creation and implementation of its American Development Model (ADM), a nationwide reinvention of how hockey was taught at the grassroots level. Based on long-term athlete development principles and founded on sport science and proven child development best practices, the ADM represents a revolution in athlete and coach development. This paper explores the research that helped create USA Hockey’s ADM, along with the initiative’s methodology, execution and early outcomes.
When Winning Hurts
Authors: Kentel Jeanne Adèle , Ramsankar David
Published: August 2016

Coaches are in a strong position to lay the groundwork for positive outcomes and attitudes in sports. In this paper we attempt to uncover ways in which coaching and sport pedagogy might be informed through our perspectives as parents of two young girls. As a father and a mother from two different families we examine the complexities of competition among the young. We begin to theorize about the ways young people might contribute to the discourse about competition in sport and ways coaches, coach educators and researchers might respond to enact potential reform.
Kinematic Analysis of Skating Technique of Olympic Skiers in the Men's 50-km Race
Authors: Smith Gerald A. , Heagy Brian S.
Published: August 2016

A project involving 3-D analysis of skiing technique during the 1992 Olympic Winter Games (Albertville, France) was carried out. This part of the project focused on the open field skating technique of the male skiers of the 50-km race. Three synchronized, high-speed video cameras were used to record the motion of all racers as they passed a site on flat terrain. Analysis was limited to those using the open field technique and whose skating cycle fit within the boundaries of the field being analyzed (n = 17). Several kinematic variables were determined: cycle velocity, cycle length, and cycle rate. Several significant correlations (p < .05) were observed related to performance: cycle velocity was positively related to cycle length (r = .76) but not cycle rate; cycle velocity and cycle length were positively related to strong side knee extension (r = .48 and r = .51, respectively). Thus, faster skiers on flat terrain tended to ski with longer cycle lengths, which perhaps derived from more vigorous knee extension.
A Mathematical Model for the Trajectory of a Spiked Volleyball and its Coaching Application
Authors: Kao Shawn S. , Sellens Richard W. , Stevenson Joan M.
Published: August 2016

A wind tunnel test was conducted to empirically determine the relationship between the Magnus force (M), spin rate (ω), and linear velocity (V) of a spiked volleyball. This relationship was applied in a two-dimensional mathematical model for the trajectory of the spiked volleyball. After being validated mathematically and empirically, the model was used to analyze three facets of play that a coach must address: the importance of topspin, possibility of overblock spiking, and optimum spiking points. It was found that topspin can increase the spiking effectiveness dramatically in many ways. It was also found that a shot spiked from about 2 m behind the net has the least possibility of being blocked.
Mathematical Model of the Takeoff Phase in the Pole Vault
Authors: Linthorne Nicholas P.
Published: August 2016

A mathematical model is presented of the takeoff phase in the pole vault for an athlete vaulting with a rigid pole. An expression is derived that gives the maximum height that the vaulter may grip on the pole in terms of the takeoff velocity, the takeoff angle, the athlete's vertical reach, and the depth of the takeoff box. Including the dependence of the vaulter's takeoff velocity on the takeoff angle reveals that there is an optimum takeoff angle that maximizes the vaulter's grip height. It is also shown that taller and faster vaulters are able to grip higher on the pole. The results of the investigation compare favorably with data for vaulters using bamboo and steel poles.
Tendon Elasticity and Relative Length: Effects on the Hill Two-Component Muscle Model
Authors: Caldwell Graham E.
Published: August 2016

The effects of relative tendon/fiber proportion and tendon elasticity on the force output of the Hill muscle model (a contractile component [CC] in series with an elastic element [SEC]) were examined through computer simulation. Three versions of the Hill model were constructed. Model 1 examined the effect of relative tendon/fiber proportion on CC kinematics and kinetics during an isometric twitch, while Model 2 compared the effect of changes in tendon compliance. These models revealed force profile differences related to alterations in CC velocity, although the reasons underlying the variation in CC kinematics were different. The relative tendon/fiber proportion and tendon compliance differences were examined in combination in Model 3. Test simulations revealed response differences among the three model versions, and therefore verified Alexander and Ker's (1990) contention that the morphology of muscle is related to design criteria. It is suggested that the implementation of generalized muscle models to represent specific units of the musculoskeletal system should be done carefully and that the implementation process itself warrants further study.
The Effect of Clipless Float Design on Shoe/Pedal interface Kinetics and Overuse Knee injuries during Cycling
Authors: Wheeler Jeffrey B. , Gregor Robert J. , Broker Jeffrey P.
Published: August 2016

Pedal kinetics, including the applied moment (Mz) about an axis orthogonal to the pedal surface and passing through the center of pressure, were measured across three shoe/pedal interface systems (toe-clip and strap, clipless fixed, clipless float) and three workrates (150, 250, 350 W) during steady-state cycling using specially developed multicompatible force pedals. The applied moment (Mz) at the pedal is an important contributor to the corresponding axial moment realized at the knee and has implications for studying overuse injury mechanics and prevention of cycling-related knee pain. Data were collected from 27 knee pain free (KPF) cyclists and 7 cyclists with cycling-related knee pain. The largest applied moments (Mz) were observed when clipless fixed pedals were employed, while clipless float pedals significantly attenuated the applied moment. Cyclists with chronic knee pain exhibited Mzpatterns markedly different from the KPF group, supporting the theory that relatively high moments, particularly internally applied moments during the power phase, may be related to knee loads and subsequent overuse injury. Our general conclusion is that clipless pedal float designs quantifiably reduce applied moments at the shoe/pedal interface without compromising power transmitted to the bike.
Effect of Velocity on Cycle Rate and Length for Three Roller Skiing Techniques
Authors: Hoffman Martin D. , Clifford Philip S. , Bender Frank
Published: August 2016

This investigation examined the adjustments made in cycle rate and length to velocity changes during roller skiing with the double pole (DP), kick double pole (KD), and VI skate (VS) techniques. Eight cross-country ski racers roller skied with each technique on a flat track at submaximal and maximal velocities while being videotaped from a lateral view. Increases in submaximal velocities were associated with increases in cycle rate and cycle length for KD and VS but only with increases in cycle rate for DP. Maximal sprint velocities were approximately 7% lower (p < .01) for KD than for DP and VS and were associated with increases (p < .01) in cycle rate for each technique combined with decreases (p < .01) in cycle length for DP and VS. The findings indicate that there are differences among techniques in the manner in which cycle rate and length are adjusted to change submaximal velocity, but each technique relies upon an increase in cycle rate to achieve maximal velocity.
Effect of Ability on Twisting Techniques in Forward Somersaults on the Trampoline
Authors: Sanders Ross H.
Published: August 2016

This study was designed to investigate the effect of ability on technique in the forward somersault with half twist (Barani) and the forward somersault with one and one half twists (Rudi) on the trampoline. Eleven trampolinists ranging in ability from elite (national representative) to early intermediate (regional representative) were analyzed using three-dimensional analysis techniques. Cumulative twist angle, rate of twist, angle of tilt of the twist axis, chest rotation, hip angle, and hip lateral flexion angle were measured. Characteristics of the arm actions were also assessed using an internal frame of reference. To generate twist in the Baranis, trampolinists tilted the axis between 5° and 14°; the amount of tilt was inversely related to ability (p < .05). In the Rudis, subjects tilted the axis between 15° and 23° using more asymmetrical arm actions and larger and more rapid hip extensions, hip lateral flexions, and chest rotations than in the Baranis. The timing and magnitude of the actions differed among the subjects and were related to ability.
Specific Movement Power Related to Athletic Performance in Weight Lifting
Authors: Funato Kazuo , Matsuo Akifumi , Fukunaga Tetsuo
Published: August 2016

In order to evaluate how mechanical power relates to athletic performance in weight lifting, specific movement power (SMP) was investigated using a newly developed dynamometer. Four simulated pull movements in weight lifting were measured: weight lifting pull (WL), second pull, back strength pull, and shoulder shrug pull. Subjects included 12 elite (EL) and 14 district (DI) level Japanese weight lifters. Athletic performance was defined as the highest total combined weight (snatch plus clean and jerk) lifted during competition. The highest SMP was observed in the WL. Force, velocity, and power relations were derived from the WL, showing higher velocity and power values in EL than DI at an identical force level. SMP in WL was found to be significantly correlated to athletic performance. SMP measured as a simulated pull movement in weight lifting employing the present dynamometer appears useful in evaluating athletic performance. Furthermore, this dynamometer provides force-velocity relationships during multiarticular explosive movements.
Three-Dimensional Kinematics of the Throwing Arm during the Penalty Throw in Water Polo
Authors: Feltner Michael E. , Nelson September T.
Published: August 2016

The purpose was to compute the instantaneous contributions of anatomical rotations of the trunk, upper arm, forearm, and hand to ball speed and to quantify the three-dimensional angular kinematics of the trunk and throwing arm during water polo penalty throws. The largest contributors to predicted ball speed |(vB)'| at release were forearm extension and a counterclockwise twisting rotation of the trunk. Upper arm internal rotation contribution to |(vB)'| at release was highly variable and exhibited a significant inverse relationship with the upper arm horizontal adduction contribution to |(vB)'| at release (r = −.70). Subjects with large internal rotation contributions to |(vB)'| tended to have the upper arm in positions of less external rotation, but internally rotating at a faster rate, at release. Subjects with large upper arm horizontal adduction contributions to |(vB)'| exhibited a trend for faster rates of upper arm horizontal adduction and positions of increased forearm pronation at release. Findings suggest that a continuum of technique styles are used by water polo players to produce ball speed at release.
Kinesiological Factors in Vertical Jump Performance: Differences Within individuals
Authors: Áragón-Vargas Luis F. , Gross M. Melissa
Published: August 2016

The purpose of this study was to examine the changes in both the coordination patterns of segmental actions and the dynamics of vertical jumping that accompany changes in vertical jump performance(VJP)occurring from trial to trial in single subjects. Ground reaction forces and video data were analyzed for 50 maximal vertical jumps for 8 subjects. It was possible to predictVJPfrom whole-body or even segmental kinematics and kinetics in spite of the small jump performance variability. Best whole-body models included peak and average mechanical power, propulsion time, and peak negative impulse. Best segmental models included coordination variables and a few joint torques and powers. Contrary to expectations,VJPwas lower for trials with a proximal-to-distal sequence of joint reversals.
Analysis of the Bobsled and Men’s Luge Events at the XVII Olympic Winter Games in Lillehammer
Authors: Brüggemann Gert-Peter , Morlock Michael , Zatsiorsky Vladimir M.
Published: August 2016

Performance in bobsled and luge events is influenced by several environmental, material/equipment, and team-related factors. This study concentrated on the influences of equipment and athlete on overall performance and compared the luge, 2-man bobsled, and 4-man bobsled competitions at the 1994 Lillehammer Winter Olympic Games. Start time and overall acceleration in the analyzed straight section showed significant correlations with the final time. It was concluded that for the top teams in bobsled and luge, fast start time and high speed at the end of the start section were prerequisites for an excellent overall performance. Driving capacities in the most difficult sections of the track were more statistically important among the top 15 competitors, especially in the luge. The influence of the runners could not be identified in either bobsled or luge competitions.
Fully Isometric Length-Force Curves of Rat Muscle Differ from Those during and after Concentric Contractions
Authors: Meijer Kenneth , Grootenboer Henk J. , Koopman Bart F.J.M. , Huijing Peter A.
Published: August 2016

The effect of various shortening histories on postshortening isometric length-force characteristics of rat medial gastrocnemlus (GM) was studied. Active muscle force and muscle geometry were analyzed after isotonic as well as isokinetic shortening. Active shortening significantly changed GM length-force characteristics (i.e., maximal muscle force, optimum muscle length, and active slack length). Muscle geometry did not change, which indicates that the observed changes in length-force curves are related to intracellular processes. Length-force curves valid during shortening, derived from postshortening characteristics, were very different from the fully isometric length-force curve. Their most remarkable feature was the absence of a negative slope. It was concluded that the length-force curve valid during active shortening strongly depends upon shortening characteristics (i.e., initial length and shortening speed). As a consequence, the traditional, fully isometric, length-force curve is a poor estimator of the length-force curve during dynamic contractions of muscle. Implications for muscle function are discussed.
The Effect of Body Roll on Hand Speed and Hand Path in Front Crawl Swimming—A Simulation Study
Authors: Payton Carl J. , Hay James G. , Mullineaux David R.
Published: August 2016

The aim of this study was to predict the effect of body roll on hand speed and hand path during the pull phase in front crawl swimming. An earlier three-segment model (Hay, Liu, & Andrews, 1993) was developed to enable the hand to move out of the plane through the shoulder parallel to the sagittal plane of the rotating trunk. Elbow flexion, shoulder abduction, and body roll angular velocities were modeled as sine or cosine functions. For a given elbow flexion, an increase in maximum body roll from 45° to 60° produced a marked increase in medial hand motion. For a given body roll, an increase in maximum elbow flexion from 60° to 90° increased medial hand motion and reduced downward hand motion. An increase in body roll increased hand speed in the plane perpendicular to the swimming direction, thus increasing the potential of the hand to develop propulsive lift forces.
Pedal and Crank Kinetics in Uphill Cycling
Authors: Caldwell Graham E. , Li Li , McCole Steve D. , Hagberg James M.
Published: August 2016

Alterations in kinetic patterns of pedal force and crank torque due to changes in surface grade (level vs. 8% uphill) and posture (seated vs. standing) were investigated during cycling on a computerized ergometer. Kinematic data from a planar cine analysis and force data from a pedal instrumented with piezoelectric crystals were recorded from multiple trials of 8 elite cyclists. These measures were used to calculate pedal force, pedal orientation, and crank torque profiles as a function of crank angle in three conditions: seated level, seated uphill, and standing uphill. The change in surface grade from level to 8% uphill resulted in a shift in pedal angle (toe up) and a moderately higher peak crank torque, due at least in part to a reduction in the cycling cadence. However, the overall patterns of pedal and crank kinetics were similar in the two seated conditions. In contrast, the alteration in posture from sitting to standing on the hill permitted the subjects to produce different patterns of pedal and crank kinetics, characterized by significantly higher peak pedal force and crank torque that occurred much later in the downstroke. These kinetic changes were associated with modified pedal orientation (toe down) throughout the crank cycle. Further, the kinetic changes were linked to altered nonmuscular (gravitational and inertial) contributions to the applied pedal force, caused by the removal of the saddle as a base of support.
A Three-Dimensional Biomechanical Analysis of the Cat Ankle Joint Complex: II. Effects of Ankle Joint Orientation on Evoked Isometric Joint Torque
Authors: Lawrence John H. , Nichols T. Richard
Published: August 2016

Muscle actions are often defined within a single anatomical reference plane. Yet animals must control posture and movement within a three-dimensional (3-D) environment, responding to a 3-D array of perturbing forces. Based on information gained regarding the 3-D muscle mechanics at the cat ankle joint complex (companion paper), we decided to study how alterations in the 3-D AJC orientation might affect ankle joint postural control. We used a 6 degree-of-freedom force-moment sensor to assess the affect of ankle joint orientation on the 3-D isometric joint torques evoked by electrical stimulation of muscles crossing the ankle joint complex (AJC) in the deeply anesthetized cat. An orthogonal axis system was established at the designated ankle rotation center, such that pitch (flexion-extension), yaw (abduction-adduction), and roll (inversion-eversion) axis torques were calculated. Experimental results suggest that both the magnitude and sign of extra-sagittal torques from the gastrocnemius muscles are joint angle dependent. Also, the hind limb levering system stabilizes the AJC against large yaw and roll rotations away from the control position.
Determining the Force-Length-Velocity Relations of the Quadriceps Muscles: II. Maximum Muscle Stress
Authors: Chow John W. , Darling Warren G. , Ehrhardt James C.
Published: August 2016

The purpose of this study was to determine the maximum muscle stress (σ), defined as the maximum isometric force divided by the physiological cross-sectional area, of the quadriceps muscles for a pilot study involving musculoskeletal modeling. One female subject performed maximum effort isometric knee extension exercises on an isokinetic dynamometer at different attachment arm angles. The gravitational effect was taken into consideration when determining the isometric resultant knee torques at different knee flexion angles. The anatomical and geometric parameters of the quadriceps muscles were obtained from radiography and magnetic resonance imaging taken from the subject. The σ value was computed using me measured knee torques, musculoskeletal parameters data, and information reported in the literature. The computation procedures used in this study represented the first attempt to incorporate the concept of optimal muscle length in the determination of maximum muscle stress. The σ values obtained from the data for nine different knee flexion angles ranged from 21.4 to 30.5 N/cm2. The average value of 25.6 ± 2.6 N/cm2 is notably smaller than the human σ values reported in the literature, but is comparable to the σ values obtained from isolated muscles.
Determining the Force-Length-Velocity Relations of the Quadriceps Muscles: III. A Pilot Study
Authors: Chow John W. , Darling Warren G. , Hay James G. , Andrews James G.
Published: August 2016

The purpose of this study was to propose and evaluate a method for the in vivo determination of the force-length-velocity relations of individual quadriceps muscles. One female subject performed maximum effort knee extensions on an isokinetic dynamometer. The gravitational and inertial effects were taken into consideration when determining the resultant knee torque. Selected anatomical and geometric parameters of the quadriceps muscles were obtained from radiography and magnetic resonance imaging (MRI). Hill’s (1938) mechanical model was used to represent the force-velocity relation of a muscle at a given length, and the constants in Hill’s model were assumed to vary with muscle length. Experimentally determined knee torque and muscle shortening velocity data were used to determine the unknown parameters in the muscle model. The relation between each muscle parameter and muscle length for each muscle was obtained using regression analysis. On average, the muscle model overestimated the knee torque by 15.5 ± 5.1%. The overestimations may have resulted from the lack of low torque-high velocity data for the determination of muscle model parameters. When a set of fixed Hill constants was used, the knee torque was underestimated by 29.0 ± 10.6%. The results demonstrate the feasibility of the method proposed in this study.
Evaluation of a Treadmill with Vibration Isolation and Stabilization (TVIS) for Use on the International Space Station
Authors: McCrory Jean L. , Lemmon David R. , Sommer H. Joseph , Prout Brian , Smith Damon , Korth Deborah W. , Lucero Javier , Greenisen Michael , Moore Jim , Kozlovskaya Inessa , Pestov Igor , Stepansov Victor , Miyakinchenko Yevgeny , Cavanagh Peter R.
Published: August 2016

A treadmill with vibration isolation and stabilization designed for the International Space Station (ISS) was evaluated during Shuttle mission STS-81. Three crew members ran and walked on the device, which floats freely in zero gravity. For the majority of the more than 2 hours of locomotion studied, the treadmill showed peak to peak Linear and angular displacements of less than 2.5 cm and 2.5°, respectively. Vibration transmitted to the vehicle was within the microgravity allocation limits that are defined for the ISS. Refinements to the treadmill and harness system are discussed. This approach to treadmill design offers the possibility of generating 1G-like loads on the lower extremities while preserving the microgravity environment of the ISS for structural safety and vibration free experimental conditions.
The Influence of Heel Fit on Rearfoot Motion in Running Shoes
Authors: Van Gheluwe Bart , Kerwin David , Roosen Philip , Tielemans Rudi
Published: August 2016

Prior research into eversional control in running has reported the occurrence of calcaneal slipping, defined as the difference between calcaneal and heel counter eversion within the shoe. Inadequate heel fit has been proposed to explain the observed slippage. Therefore, the purpose of the current study was to investigate whether eliminating excess space around the calcaneus by narrowing the heel counter or by introducing heel inserts could minimize eversional slipping of the calcaneus within the shoe and, in so doing, improve eversion control of the calcaneus. Three-dimensional rearfoot kinematics of 20 subjects running on a treadmill at 3.8 m · s−1 were recorded using a three-camera Vicon movement analysis system. ANOVA analyses of the angular displacement data revealed a significant (p < .05) reduction in maximal eversion of the calcaneus in shoes with a narrower heel fit though the heel counter of the same shoes displayed more eversion than their wider counterparts. Calcaneal eversion in the shoes with a wider heel counter, however, could be reduced significantly (p < .05) using heel inserts. Maximal relative eversion (referenced to the value at heel strike) and eversional velocity were only affected by the heel inserts, the latter, however, not significantly. All these results show that heel fit affects the eversional behavior of the calcaneus during ground contact and that running shoes equipped with a rigid heel counter will improve rearfoot control, thus only reducing the risk for overload injuries if a snug heel fit used.
Normal and ACL-Deficient in Situ Measurement of Patellofemoral Joint Contact
Authors: Boyd Steven K. , Ronsky Janet L.
Published: August 2016

Abnormal joinl coniact mechanics in the knee joint due to loss of anterior cruciate ligament (ACL) are often speculated to play an important role in the development of osteoarthritis. In this study, a technique was developed so that contact of the patellofemoral (PF) joint could be estimated in situ using a mathematical contact model. The model inputs were PF joint kinematics measured in situ and the PF joint surface topology. Due to the small size of the joint, techniques for measuring joinl kinematics and surface topology with sufficient precision were paramount so that reasonable estimates of joint contact could be obtained. The sensitivity of the model to measurement errors was examined. Differences in joint contact between ACL-intacl and ACL-deficient conditions were analyzed. Statistically significant differences in contact areas were detected between the intact and ACL-deficient knee joint, and different coniact areas and locations as a function of joint angle and quadriceps muscular stimulation.
The Effect of Strength Shoes on Muscle Activity during Quiet Standing
Authors: Frank Karl , Baratta Richard V. , Solomonow Moshe , Shilstone Mackie , Riché Kevin
Published: August 2016

The goal of this work was to study the effect of Strength Shoes on the activity of leg and postural muscles to gain insight into the mechanisms by which the shoes may improve athletic performance. Surface EMG signals were obtained from the tibialis anterior, medial gastrocnemius, rectus femoris, biceps femoris, gluteus maximus, and erector spinae of 18 healthy athletic subjects. The subjects stood quietly while wearing either normal athletic shoes or Strength Shoes. EMG root mean square value was compared in each muscle using trimmed paired t tests. Significant (p < .002) increases in EMG activity were found in the MG, TA, GM, and ES muscles when the subjects were wearing Strength Shoes as compared to normal shoes. These changes served to stiffen the ankle, counteracting the dorsiflexion moment created by the shoes, and to support an anterior leaning posture, which compensates for the anterior shift in center of pressure. No significant changes were detected in the activities of RF or BF muscles. Using Strength Shoes increased activity in the triceps surae complex and in other muscles mat support the changes in postural requirements caused by the anterior shift in center of pressure.
The Role of Shoulder and Hip Torques Generated during a Backward Giant Swing on Rings
Authors: Sprigings Eric J. , Lanovaz Joel L. , Russell Keith W.
Published: August 2016

Backward giant swings on rings were performed by 2 elite gymnasts from both a stationary and a swinging handstand position. One of the ring cables was instrumented so that tension values could be recorded. Muscle torques and corresponding power profiles for the hip and shoulder joints were calculated and used to interpret the movement patterns displayed by the gymnasts. The hip-flexors played a primary role in preventing excessive hyper-extension of the hip joint during the downward swing. Overall, during the backward giant swing, the hip-joint flexors/extensors acted as a net energy sink for the system rather than as a source of energy generation. The piking motion that was observed to take place just past the bottom of the swing was primarily due to the momentum built up in the legs during the rapid straightening of the body during the bottom of the swing. The shoulder flexors/extensors functioned as the primary source of energy generation to the system. From a swinging handstand, with an initial handstand swing amplitude of 16°, the gymnasts were able to arrive at the next handstand position with approximately 6–7.5° of residual swing, which was close to the optimal value of 4° predicted by computer simulation.
The Influence of High Heeled Shoes on Kinematics, Kinetics, and Muscle EMG of Normal Female Gait
Authors: Stefanyshyn Darren J. , Nigg Benno M. , Fisher Veronica , O'Flynn Barry , Liu Wen
Published: August 2016

The purpose of this investigation was to determine whether a graded response in gait kinematics, kinetics, and EMG occurs as shoe heel height increases. Four different shoes, including one flat shoe and three shoes with high heels, were tested in this investigation. The average heel heights of the four shoes were 1.4 cm, 3.7 cm, 5.4 cm, and 8.5 cm. Kinematics, kinetics, and muscle EMG were measured during the stance phase of gait on 13 healthy female subjects while wearing each of these 4 shoes. Systematic increases in the active vertical, propulsive, and braking forces were found as shoe height increased. Ankle and knee flexion and soleus and rectus femoris activity showed a graded response as heel height increased. One surprising result was the behavior of the maximal vertical impact force peak and the maximal loading rate during heel impact. The vertical impact force peaks and the maximal vertical loading rates were highest for the shoe with 3.7 cm heel height and lowest for the flat shoe and the shoe with heel height of 8.5 cm.
Plantar Pressures during Ski Jumping Take-Off
Authors: Virmavirta Mikko , Komi Paavo V.
Published: August 2016

The Paromed Datalogger® with two insole pressure transducers (16 sensors each, 200 Hz) was applied to study the feasibility of the system for measurement of plantar pressure distribution in ski jumping. The specific aim was to test the sensitivity of the Paromed system to the changes in plantar pressure distribution in ski jumping. Three international level ski jumpers served as subjects during the testing of the system. The Datalogger was fixed to the jumpers’ lower back under the jumping suit. A separate pulse was transmitted to the Datalogger and tape recorder in order to synchronize the logger information with photocell signals indicating the location of the jumper on the inrun. Test procedure showed that this system could be used in ski jumping with only minor disturbance to the jumper. The measured relative pressure increase during the inrun curve matched well the calculated relative centrifugal force (mv2 · r‒1), which thus serves a rough estimation of the system validity. Strong increase in pressure under the big toes compared to the heels (225% and 91%, respectively) with large interindividual differences characterized the take-off. These differences may reflect an unstable anteroposterior balance of a jumper while he tries to create a proper forward rotation for a good flight position.
Stability Landscapes of Walking and Running Near Gait Transition Speed
Authors: Li Li
Published: August 2016

Variability has long been used as an indication of stability in the application of a dynamical systems approach to human motion (i.e., greater variability has been related to a less stable system and vise versa). This paper incorporates the probability of gait transition during walking and running at a certain speed to represent the stability of human locomotion. The mathematical representation concerning the probability of gait transition change with locomotory speed was derived for increasing walking speed and decreasing running speed. Additionally, the influence of acceleration and deceleration on the stability landscapes of walking and running was discussed based on experimental data. The influence of acceleration was also used to explain the different trends of hysteresis observed by various researchers. Walk-to-run transition speed was greater than run-to-walk transition speed, with a greater magnitude of acceleration, while the trend was reversed with a lesser acceleration magnitude. The quantitative measure of the relationship between variability and stability needs to be explored in the future.
Comparison of Kinematic and Temporal Parameters between Different Pitch Velocity Groups
Authors: Matsuo Tomoyuki , Escamilla Rafael F. , Fleisig Glenn S. , Barrentine Steven W. , Andrews James R.
Published: August 2016

This study investigated differences in kinematic and temporal parameters between two velocity groups of baseball pitchers. Data were collected from 127 healthy college and professional baseball pitchers. Those who threw faster than 1 SD above the sample mean (>38.0 m/s) were assigned to the high velocity group (n = 29), and those who threw slower than 1 SD below the sample mean (<34.2 m/s) were assigned to the low velocity group (n = 23). Twelve kinematic parameters and 9 temporal parameters were measured and analyzed. The pattern of lead knee movement was also investigated. Maximum shoulder external rotation, forward trunk tilt at the instant of ball release, and lead knee extension angular velocity at the instant of ball release were significantly greater in the high velocity group. Maximum lead knee flexion angular velocity was significantly greater in the low velocity group. Seventy percent of the high velocity group showed knee extension during the approach to ball release, whereas the low velocity group showed a variety of knee movement patterns involving less knee extension and more knee flexion. The greater shoulder external rotation in the high velocity group produced an increased range of motion during the acceleration phase.
Sources of Error in Determining Countermovement Jump Height with the Impulse Method
Authors: Street Glenn , McMillan Scott , Board Wayne , Rasmussen Mike , Heneghan J. Michael
Published: August 2016

A comprehensive error analysis was performed on the impulse method. To evaluate the potential errors, jump height was recalculated after altering one of the measurement or calculation techniquaes while leaving the others unchanged, and then comparing it to the reference jump height (best estimate of true jump height). Measurement techniques introduced the greatest error. Low-pass filters with cutoff frequencies < 580 Hz led to systematic underestimations of jump height, ≤26%. Low sampling frequencies (<1,080 Hz) caused jump height to be underestimated by ≤4.4%. Computational methods introduced less error. Selecting takeoff too early by using an elevated threshold caused jump height to be overestimated by ≤1.5%. Other potential sources of computational error: (a) duration of body weight averaging period; (b) method of integration; (c) gravity constant; (d) start of integration; (e) duration of offset averaging period; and (f) sample duration, introduced < 1% error to the calculated jump height. Employing the recommended guidelines presented in this study reduces total error to ≤ ±0.76%. Failing to follow the guidelines can lead to average errors as large as 26%.
Stresses in the Growth Plate of the Developing Proximal Femur
Authors: Ribble Thomas G. , Santare Michael H. , Miller Freeman
Published: August 2016

Finite element models of the proximal femur at birth, 2 years of age, and at 8 years of age were constructed to investigate stress patterns under different loading conditions. These loading conditions represent typical activities of a normal developing child and abnormal activity associated with muscle spasticity. The hypothesis is that the shear stresses in the growth plate correlate with the neckshaft angle as associated with valgus and normal development. Loads for the finite element models were derived from a separate muscle model used to calculate the forces across the hip joint for an arbitrary subject and activity. Results show there is an inverse relationship between the relative magnitude of the shear stress in the growth plate and the developing neck-shaft angle. The relatively high shear stresses generated by normal activity in the 2-year-old’s growth plate correlate with the decrease in neck-shaft angle that accompanies normal development. Alternatively, lower shear stresses are generated in the growth plate by loading conditions representing spasticity. These lower magnitude shear stresses correlate with a valgus deformity, which is often observed clinically.