Search Results

You are looking at 1 - 10 of 126 items for :

  • "mechanical properties" x
Clear All
Restricted access

Enrique Colino, Jorge Garcia-Unanue, Leonor Gallardo, Carl Foster, Alejandro Lucia and Jose Luis Felipe

Surface properties can influence endurance running performance. 1 – 3 Indeed, athletes adjust their leg stiffness when running on surfaces of differing mechanical properties, 4 , 5 resulting in subtle changes in lower-limb kinematic patterns, landing style, stride length, ground reaction force

Restricted access

Scott W. Cheatham and Russell Baker

researchers attribute the variability to different study methods and the use of different tape brands. A common hypothesized cause of the variability is that the various tape brands have different mechanical properties due to different manufacturing processes. 3 – 5 This has prompted researchers to measure

Restricted access

Joseph J. Crisco, Elizabeth I. Drewniak, Martin P. Alvarez and David B. Spenciner

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 It appears that current governing body specifications are outdated, as no ball model we tested met these specifications.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

Restricted access

Thomas A. Haugen, Felix Breitschädel and Stephen Seiler

), P max (0.6, ±0.6 W·kg −1 ; possibly; small), and RF max (0.4, ±0.3%, possibly; small). Discussion In the current investigation of sprinting handball and basketball players, substantial differences in sprint mechanical properties were observed across playing standards and positions. National team

Restricted access

Ryu Nagahara, Alberto Botter, Enrico Rejc, Masaaki Koido, Takeshi Shimizu, Pierre Samozino and Jean-Benoit Morin

Purpose:

To test the concurrent validity of data from 2 different global positioning system (GPS) units for obtaining mechanical properties during sprint acceleration using a field method recently validated by Samozino et al.

Methods:

Thirty-two athletes performed maximal straight-line sprints, and their running speed was simultaneously measured by GPS units (sampling rate: 20 or 5 Hz) and either a radar or laser device (devices taken as references). Lower-limb mechanical properties of sprint acceleration (theoretical maximal force, theoretical maximal speed, maximal power) were derived from a modeling of the speed–time curves using an exponential function in both measurements. Comparisons of mechanical properties from 20- and 5-Hz GPS units with those from reference devices were performed for 80 and 62 trials, respectively.

Results:

The percentage bias showed a wide range of overestimation or underestimation for both systems (-7.9% to 9.7% and -5.1% to 2.9% for 20- and 5-Hz GPS), while the ranges of its 90% confidence limits for 20-Hz GPS were markedly smaller than those for 5-Hz GPS. These results were supported by the correlation analyses.

Conclusions:

Overall, the concurrent validity for all variables derived from 20-Hz GPS measurements was better than that obtained from the 5-Hz GPS units. However, in the current state of GPS devices’ accuracy for speed–time measurements over a maximal sprint acceleration, it is recommended that radar, laser devices, and timing gates remain the reference methods for implementing the computations of Samozino et al.

Restricted access

John H. Challis, Chloe Murdoch and Samantha L. Winter

The purpose of this study was to compare the heel pad mechanical properties of runners, who repetitively load the heel pad during training, with cyclists who do not load their heel pads during training. Ten competitive long distance runners and 10 competitive cyclists volunteered for this study. The thickness of the unloaded heel pad was measured using realtime B-mode ultrasonography. A heel pad indentation device was used to measure the mechanical properties of the heel pads. To evaluate the differences between the two groups, in heel pad properties, a repeat measures analysis of variance was used (p < .05). Heel pad thickness was not different between groups when normalized with respect to subject height. There was no significant difference between the groups in percentage energy loss during loading and unloading (runners: 61.4% ± 8.6; cyclists: 62.5% ± 4.6). Heel pad stiffness for the runners was statistically significantly less than that of the cyclists (p = .0018; runners: 17.1 N·mm−1 ± 3.0; cyclists: 20.4 N·mm−1 ± 4.0). These results indicate that the nature of the activity undertaken by individuals may influence their heel pad properties. This finding may be important when considering differences in heel pad properties between different populations.

Restricted access

Ryu Nagahara, Jean-Benoit Morin and Masaaki Koido

Purpose:

To assess soccer-specific impairment of mechanical properties in accelerated sprinting and its relation with activity profiles during an actual match.

Methods:

Thirteen male field players completed 4 sprint measurements, wherein running speed was obtained using a laser distance-measurement system, before and after the 2 halves of 2 soccer matches. Macroscopic mechanical properties (theoretical maximal horizontal force [F0], maximal horizontal sprinting power [Pmax], and theoretical maximal sprinting velocity [V0]) during the 35-m sprint acceleration were calculated from speed–time data. Players’ activity profiles during the matches were collected using global positioning system units.

Results:

After the match, although F0 and Pmax did not significantly change, V0 was reduced (P = .038), and the magnitude of this reduction correlated with distance (positive) and number (negative) of high-speed running, number of running (negative), and other low-intensity activity distance (negative) during the match. Moreover, Pmax decreased immediately before the second half (P = .014).

Conclusions:

The results suggest that soccer-specific fatigue probably impairs players’ maximal velocity capabilities more than their maximal horizontal force-production abilities at initial acceleration. Furthermore, long-distance running, especially at high speed, during the match may induce relatively large impairment of maximal velocity capabilities. In addition, the capability of producing maximal horizontal power during sprinting is presumably impaired during halftime of a soccer match with passive recovery. These findings could be useful for players and coaches aiming to train effectively to maintain sprinting performance throughout a soccer match when planning a training program.

Restricted access

Elizabeth I. Drewniak, David B. Spenciner and Joseph J. Crisco

Sudden death resulting from ventricular fibrillation (VF) caused by a nonpenetrating chest wall impact, known as commotio cordis (CC), is the second leading cause of death among young athletes. To date, seven young athletes wearing chest protectors have died from CC. The purpose of this study was to determine whether a relationship exists between mechanical properties of chest protectors and occurrence of VF, previously determined by Weinstock et al., using an established swine model. A servo-hydraulic material tester was used to determine properties of the chest protectors, including displacement, permanent deformation, stiffness, and area of pressure distribution. These properties were then compared with the occurrence of VF. We found that a decreased proportion of hits resulting in VF was significantly associated (R 2 = 0.59, p = 0.001) with an increase in the area of pressure distribution. These findings are a limited, but crucial, first step in understanding the prevention of this complex and perplexing phenomenon.

Restricted access

Keitaro Kubo, Takanori Teshima, Norikazu Hirose and Naoya Tsunoda

The purpose of this study was to compare the morphological and mechanical properties of the human patellar tendon among elementary school children (prepubertal), junior high school students (pubertal), and adults. Twenty-one elementary school children, 18 junior high school students, and 22 adults participated in this study. The maximal strain, stiffness, Young’s modulus, hysteresis, and cross-sectional area of the patellar tendon were measured using ultrasonography. No significant difference was observed in the relative length (to thigh length) or cross-sectional area (to body mass2/3) of the patellar tendon among the three groups. Stiffness and Young’s modulus were significantly lower in elementary school children than in the other groups, while no significant differences were observed between junior high school students and adults. No significant differences were observed in maximal strain or hysteresis among the three groups. These results suggest that the material property (Young’s modulus) of the patellar tendons of elementary school children was lower than that of the other groups, whereas that of junior high school students was already similar to that of adults. In addition, no significant differences were observed in the extensibility (maximal strain) or viscosity (hysteresis) of the patellar tendon among the three groups.

Restricted access

Oscar Martel, Juan F. Cárdenes, Gerardo Garcés and José A. Carta

Anterior cruciate ligament (ACL) reconstruction is one of the most important aspects of knee surgery. For this purpose, several fixation devices have been developed, although the interference screw is the most frequently used. The most typical biomechanical test of these devices consists of placing them in a testing machine and subjecting them to a pull-out test. However, insufficient attention has been paid to the influence of the displacement test rate on the mechanical properties of the fixation system. The aim of this study is to compare the influence of the crosshead rate in the biomechanical test of two different devices for the fixation of ACL tendon grafts. One hundred in vitro tests were performed using porcine tibiae and bovine tendons. The fixation devices used were (1) an interference screw and (2) a new expansion device. All ACL reconstructions were subjected to pull-out test to failure. Five crosshead rates were employed in a range from 30 mm/min to 4000 mm/min. Statistical analyses of the results show that, for the two devices, the rate has a significant effect on both maximum force and stiffness. Moreover, the new expansion device showed lesser dependency on the crosshead rate than the interference screw.