A simulation and optimization procedure was constructed to investigate the relationships between optimal movement and muscular strength for baseball pitching. Four segments (torso, upper arms, lower arms, hands) and six torque generators (shoulders, elbows, wrists) are modeled. The torque generators have torque-angle and torque-angular velocity characteristics of Hill-type muscle function. The optimization objective function includes release velocity and negative terms penalizing joint loading and inaccuracy. The weighting coefficient for joint loads has a strong influence on the results. As this coefficient increases, the motion becomes more similar to actual measured pitches. Combining active state patterns optimized for different weighting coefficients gives larger joint loads in the simulated motion. This supports the hypothesis that well-coordinated active states are important for controlling the relationships of the different torque generators in order to create a reasonable and effective pitching motion. The model proposed here is superior to previous simulations for throwing, from the viewpoint of modeling with characteristics of Hill-type muscle function, and can be used to explore realistic baseball pitching.
Norihisa Fujii and Mont Hubbard
Brent L. Arnold
Alexandra S. Voloshina and Daniel P. Ferris
Studying human and animal locomotion on an uneven terrain can be beneficial to basic science and applied studies for clinical and robotic applications. Traditional biomechanical analysis of human locomotion has often been limited to laboratory environments with flat, smooth runways and treadmills. The authors modified a regular exercise treadmill by attaching wooden blocks to the treadmill belt to yield an uneven locomotion surface. To ensure that these treadmill modifications facilitated biomechanical measurements, the authors compared ground reaction force data collected while a subject ran on the modified instrumented treadmill with a smooth surface with data collected using a conventional instrumented treadmill. Comparisons showed only minor differences. These results suggest that adding an uneven surface to a modified treadmill is a viable option for studying human or animal locomotion on an uneven terrain. Other types of surfaces (eg, compliant blocks) could be affixed in a similar manner for studies on other types of locomotion surfaces.
Jason Wicke and Becky Lopers
An elliptical cylinder model developed by Jensen (1978) has been a widely accepted method for determining human segment inertial parameters. The goal of the present study was to evaluate the accuracy of the segment volume calculation step of this model. Three possible sources of error were examined: between-sex differences in body shape, image ratio, and human inconsistencies in digitizing. Volume estimates for the right lower arm + right hand, right lower leg + right foot, and whole body on 20 young men and women were calculated from digitized images at a ratio of 1:10 and 1:5 of the actual size (measured) and compared to values measured using an underwater displacement technique (criterion). Results showed no differences between the sexes on the accuracy of estimating the three volumes at either image ratio. Combining both sexes, the error in calculating segment volumes with an image-to-actual-size ratio of 1:10 were significantly larger, p < 0.05, than at a ratio of 1:5 for both the lower arm + hand (4.28 ± 2.92% vs. –0.43 ± 2.49%) and the whole body (4.80 ± 2.49% vs. 2.01 ± 2.17%). There was no significant change in mean for the lower leg + foot when the image was increased from 1:10 to 1:5 (–0.12 ± 3.92% vs. –0.81 ± 3.01%, respectively). Although not statistically significant, p > 0.05, a greater magnification seemed to have also reduced the influence of human inconsistencies, which was found to be a primary source of error. When the image-to-actual-size ratio is high (i.e., 1:5) and precaution is taken during digitization, the elliptical cylinder model provides accurate estimates of segment volumes of the whole body and extremities.
Prue Cormie, Jeffrey M. McBride and Grant O. McCaulley
The objective of this study was to investigate the validity of power measurement techniques utilizing various kinematic and kinetic devices during the jump squat (JS), squat (S) and power clean (PC). Ten Division I male athletes were assessed for power output across various intensities: 0, 12, 27, 42, 56, 71, and 85% of one repetition maximum strength (1RM) in the JS and S and 30, 40, 50, 60, 70, 80, and 90% of 1RM in the PC. During the execution of each lift, six different data collection systems were utilized; (1) one linear position transducer (1-LPT); (2) one linear position transducer with the system mass representing the force (1-LPT+MASS); (3) two linear position transducers (2-LPT); (4) the force plate (FP); (5) one linear position transducer and a force plate (1-LPT+FP); (6) two linear position transducers and a force place (2-LPT+FP). Kinetic and kinematic variables calculated using the six methodologies were compared. Vertical power, force, and velocity differed significantly between 2-LPT+FP and 1-LPT, 1-LPT+MASS, 2-LPT, and FP methodologies across various intensities throughout the JS, S, and PC. These differences affected the load–power relationship and resulted in the transfer of the optimal load to a number of different intensities. This examination clearly indicates that data collection and analysis procedures influence the power output calculated as well as the load–power relationship of dynamic lower body movements.
Shannon David, Kim Gray, Jeffrey A. Russell and Chad Starkey
The original and modified Ottawa Ankle Rules (OARs) were developed as clinical decision rules for use in emergency departments. However, the OARs have not been evaluated as an acute clinical evaluation tool.
To evaluate the measures of diagnostic accuracy of the OARs in the acute setting.
The OARs were applied to all appropriate ankle injuries at 2 colleges (athletics and club sports) and 21 high schools. The outcomes of OARs, diagnosis, and decision for referral were collected by the athletic trainers (ATs) at each of the locations. Contingency tables were created for evaluations completed within 1 h for which radiographs were obtained. From these data the sensitivity, specificity, positive and negative likelihood ratios, and positive and negative predictive values were calculated.
The OARs met the criteria for radiographs in 100 of the 124 cases, of which 38 were actually referred for imaging. Based on radiographic findings in an acute setting, the OARs (n = 38) had a high sensitivity (.88) and are good predictors to rule out the presence of a fracture. Low specificity (0.00) results led to a high number of false positives and low positive predictive values (.18).
When applied during the first hour after injury the OARs significantly overestimate the need for radiographs. However, a negative finding rules out the need to obtain radiographs. It appears the AT’s decision making based on the totality of the examination findings is the best filter in determining referral for radiographs.
Steve B. Downs and Terry M. Wood
This study examined the validity and reliability of a Volleyball Skills Assessment Test (VSAT) as a measure of volleyball skill and as a predictor of team success in Special Olympics International (SOI) volleyball competition. Test-retest reliability data from 130 SOI volleyball players with mental retardation (101 males and 29 females) in the sixth week of an SOI volleyball training program yielded intraclass reliability coefficients (R) above .80 for all VSAT subtests (forearm pass, spike, set, serve) across gender with the exception of the set test for females (R = .75). Multivariate test battery test–retest reliability, examined using canonical correlation analysis, yielded moderate total redundancy estimates ranging between 62.5 and 66.1%. A high degree of concurrent validity was evidenced when correlating VSAT scores with judges’ ratings of performance on the four skills: r = .93 (r 2 = .86) serve, r = .94 (r 2 = .88) pass, r = .98 (r2 = .96) spike, and r = .86 (r2 = .74) set. Contingency table analysis, multiple regression, and discriminant function analysis revealed that the predictive validity of the VSAT as the primary determinant for allocating teams to pools of equal ability is questionable.
Lee N. Burkett, Jack Chisum, Ralph Cook, Bob Norton, Bob Taylor, Keith Ruppert and Chris Wells
Numerous studies in the past 30 years have researched physiological adaptation to stress by wheelchair-bound subjects. Instrumentation necessary to produce this effect had to be designed and tested prior to obtaining valid data. This study had two main purposes: to design a wheelchair ergometer for physiological testing of spinal cord-injured subjects, and to demonstrate the validity of the maximal stress test when using the wheelchair ergometer. To test the validity of the wheelchair ergometer, 10 disabled subjects (9 paraplegic and 1 quadriplegic) participated in both a maximal field test (FT) and a maximal wheelchair ergometer test (WERG), with each subject serving as his or her own control. A randomly assigned counterbalanced design (5 subjects assigned to complete the FT first, with the second group of 5 subjects completing the WERG first) was used to reduce the learning effect in the study. The results of the t-tests indicated there was no significant difference between V̇O2 and V̇E, (STPD) averages for the WERG and FT for maximal effort with two-tailed significant levels of t = .9016 and t = .7294, respectively. The Pearson product moment correlation level was statistically significant at p < .0001, when the WERG V̇O2 was compared to the FT V̇O2 (r = .94), and was significant at p < .005 when the WERG V̇E was compared to the FT V̇E (r = .82).
Abu B. Yilla and Claudine Sherrill
The purpose was to develop a valid and reliable battery of quad rugby skill tests. Participants were 65 adult, male, quad rugby athletes. Content validity was established in two modified Delphi rounds by a panel of international experts. For concurrent validity, Spearman rho correlations between coaches’ rankings of players’ skills and scores ranged from .63 to .98 for the total battery. For construct validity, principal factor analysis with oblique rotation revealed two factors. Intraclass reliability coefficients ranged from .94 to .99. The battery includes five tests: maneuverability with the ball, pass for accuracy, picking, sprinting, and pass for distance.
Samantha L. Winter and John H. Challis
The muscle fiber force–length relationship has been explained in terms of the cross-bridge theory at the sarcomere level. In vivo, for a physiologically realistic range of joint motion, and therefore range of muscle fiber lengths, only part of the force–length curve may be used; that is, the section of the force– length curve expressed can vary. The purpose of this study was to assess the accuracy of a method for determining the expressed section of the force– length curve for biarticular muscles. A muscle model was used to simulate the triceps surae muscle group. Three model formulations were used so that the gastrocnemius operated over different portions of the force–length curve: the ascending limb, the plateau region, and the descending limb. Joint moment data were generated for a range of joint configurations and from this simulated data the region of the force– length relationship that the gastrocnemius muscle operated over was successfully reconstructed using the algorithm of Herzog and ter Keurs (1988a). Further simulations showed that the correct region of the force–length curve was accurately reconstructed even in the presence of random and systematic noise generated to reflect the effects of sampling errors, and incomplete muscle activation.