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Robin S. Vealey, Robin Cooley, Emma Nilsson, Carly Block and Nick Galli

effectiveness as a consultant     Coaches/administrators like to have quantitative data   Cross-validate observations/interviews Validation of my observations; cross-checking with interviews     Identify discrepancies between objective and subjective data   Selection Draft selection Build Relationships Rapport

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Anthony S. Kulas, Randy J. Schmitz, Sandra J. Shultz, Mary Allen Watson and David H. Perrin

Although leg spring stiffness represents active muscular recruitment of the lower extremity during dynamic tasks such as hopping and running, the joint-specific characteristics comprising the damping portion of this measure, leg impedance, are uncertain. The purpose of this investigation was to assess the relationship between leg impedance and energy absorption at the ankle, knee, and hip during early (impact) and late (stabilization) phases of landing. Twenty highly trained female dancers (age = 20.3 ± 1.4 years, height = 163.7 ± 6.0 cm, mass = 62.1 ± 8.1 kg) were instrumented for biomechanical analysis. Subjects performed three sets of double-leg landings from under preferred, stiff, and soft landing conditions. A stepwise linear regression analysis revealed that ankle and knee energy absorption at impact, and knee and hip energy absorption during the stabilization phases of landing explained 75.5% of the variance in leg impedance. The primary predictor of leg impedance was knee energy absorption during the stabilization phase, independently accounting for 55% of the variance. Future validation studies applying this regression model to other groups of individuals are warranted.

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Mark L. McMulkin, Jeffrey C. Woldstad and Richard E. Hughes

Biomechanical optimization models are often used to estimate muscular and intervertebral disc forces during physical exertions. The purpose of this study was to determine whether an optimization-based biomechanical model predicts torso muscular activity of males and females equally well. The Minimum Intensity Compression (MIC) model, which has been extensively applied in industrial ergonomic task analysis, was used to estimate muscle forces for 3D moments. Participants (6 M, 6 F) performed 18 isometric exertions resisting 3D L3/L4 moments while electromyographic (EMG) activity was recorded for 8 muscles. Overall, model force estimates correlated better with male EMG activity (R 2 = 0.43) than with female EMG activity (R 2 = 0.33). Model force estimates of 4 muscles (LRA, RRA, REO, and RES) correlated better with male EMG activity than with female EMG. We conclude that trunk muscle forces estimated by current biomechanical modeling do not correlate equally well to male and female EMG activity. Future research needs to address validation or improvement of biomechanical trunk models for females.

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John F. Swigart, Arthur G. Erdman and Patrick J. Cain

A new method for quantifying shoe cushioning durability was developed. This method used a computer-controlled, closed-loop materials testing system to subject the shoes to force-time profiles that were indicative of running. The change in the magnitude of the maximum energy absorbed by a shoe and the change in the magnitude of the energy balance of the shoe were quantified after the shoe had been worn running for a given distance. A shoe that changed very little in these quantities had a small energy wear factor and was deemed to have durable cushioning. The test method was roughly validated through comparison of three shoes of different midsole constructions with known relative durabilities. The shoes were tested at four simulated running speeds for energy properties when they were new and after they were run in for 161 km. The relative durabilities of the tested shoes were consistent with expectations based on the shoes' materials and constructions, showing that the new method has promise in predicting shoe cushioning durability, and thus more complete studies of the method may prove useful.

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Boris I. Prilutsky

In this response, the major criticisms of the target article are addressed. Terminology from the target article that may have caused some confusion is clarified. In particular, the tasks that have the basic features of muscle coordination, as identified in the target article, have been limited in scope. Anew metabolic optimization criterion suggested by Alexander (2000) is examined for its ability to predict muscle coordination in walking. Issues concerning the validation of muscle force predictions, the rules of muscle coordination, and the role of directional constraints in coordination of two-joint muscles are discussed. It is shown in particular that even in one-joint systems, the forces predicted by the criterion of Crowninshield and Brand (1981) depend upon the muscle moment arms and the physiological cross-sectional areas in much more complex ways than either previously assumed in the target article, or incorrectly derived by Herzog and Ait-Haddou (2000). It is concluded that the criterion of Crowninshield and Brand qualitatively predicts the basic coordination features of the major one- and two-joint muscles in a number of highly skilled, repetitive motor tasks performed by humans under predictable conditions and little demands on stability and accuracy. A possible functional significance of such muscle coordination may be the minimization of perceived effort, muscle fatigue, and/or energy expenditure.

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Suzanne LaScalza, Linda N. Gallo, James E. Carpenter and Richard E. Hughes

Clinical observation suggests that shoulder pathologies such as rotator cuff disorders and shoulder instability may alter the normal shoulder rhythm or relative motions of the structures comprising the shoulder girdle. The purpose of this study was to assess the accuracy of using a skin-mounted humeral cuff that could be used in vivo to determine Euler rotation angles and the helical axis of motion (HAM) during upper extremity movements. An in vitro model was used to compare the kinematics determined from the externally applied humeral cuff to the kinematics measured directly from the humerus. The upper extremities of five cadavers were moved through several humerus and forearm motion trials. Measurements from the humeral cuff were compared directly to the bone measurements for all trials to determine the accuracy of the Euler rotation angles. In evaluating the HAM, the orientation, location, and magnitude of rotation were compared either to the bone measurements or to the known rotational axis of the testing fixture. Euler rotation angles and the helical axis of motion determined by the measurements taken from the skin-mounted humeral cuff were very similar to those using the measurements from the bone-mounted sensor. The humeral cuff was shown to provide a viable, noninvasive method for determining the Euler rotation angles and helical axis of motion during 3-D humeral movements. The validation makes the humeral cuff a valuable tool for examining the effect of shoulder pathologies on the kinematics of the upper extremity.

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Sabrina S.M. Lee, Gregory S. Lewis and Stephen J. Piazza

The accuracy of an algorithm for the automated tracking of tendon excursion from ultrasound images was tested in three experiments. Because the automated method could not be tested against direct measurements of tendon excursion in vivo, an indirect validation procedure was employed. In one experiment, a wire “phantom” was moved a known distance across the ultrasound probe and the automated tracking results were compared with the known distance. The excursion of the musculotendinous junction of the gastrocnemius during frontal and sagittal plane movement of the ankle was assessed in a single cadaver specimen both by manual tracking and with a cable extensometer sutured to the gastrocnemius muscle. A third experiment involved estimation of Achilles tendon excursion in vivo with both manual and automated tracking. Root mean squared (RMS) error was calculated between pairs of measurements after each test. Mean RMS errors of less than 1 mm were observed for the phantom experiments. For the in vitro experiment, mean RMS errors of 8–9% of the total tendon excursion were observed. Mean RMS errors of 6–8% of the total tendon excursion were found in vivo. The results indicate that the proposed algorithm accurately tracks Achilles tendon excursion, but further testing is necessary to determine its general applicability.

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Jeremy R. Dicus and Jeff G. Seegmiller

Few ankle inversion studies have taken anticipation bias into account or collected data with an experimental design that mimics actual injury mechanisms. Twenty-three participants performed randomized single-leg vertical drop landings from 20 cm. Subjects were blinded to the landing surface (a flat force plate or 30° inversion wedge on the force plate). After each trial, participants reported whether they anticipated the landing surface. Participant responses were validated with EMG data. The protocol was repeated until four anticipated and four unanticipated landings onto the inversion wedge were recorded. Results revealed a significant main effect for landing condition. Normalized vertical ground reaction force (% body weights), maximum ankle inversion (degrees), inversion velocity (degrees/second), and time from contact to peak muscle activation (seconds) were significantly greater in unanticipated landings, and the time from peak muscle activation to maximum VGRF (second) was shorter. Unanticipated landings presented different muscle activation patterns than landings onto anticipated surfaces, which calls into question the usefulness of clinical studies that have not controlled for anticipation bias.

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Kyoung-Seok Yoo, Hyun-Kyung Kim and Jin-Hoon Park

The present study examined the technical characteristics of sliding performance from push-off until stone release in curling delivery. Five elite performance level curlers (> 7 years experience) and five subelite level curlers (< 3 years experience) were analyzed during the action of delivery of a curling stone. The joint angles, angular velocities, and moments of the body center of mass (COM) were determined based on three-dimensional kinematic data. The plantar pressure data were measured using a validated in-shoe system. The results indicated that the gliding time and horizontal velocity of the mass center of the body during the sliding phase were not significantly different between the elite and subelite groups. However, there were significant differences in the gliding distance and the rate of changes in velocity profiles of body COM between the two groups. The moment of the body COM from its relative position to the ankle of the support limb in the anterior/posterior direction was positive in elite curlers and negative in subelite curlers. In addition, larger ankle dorsiflexion and greater contact area of the sliding foot were observed in elite curlers. These data suggest a superior ability of elite curlers to maintain a regulated movement speed and balance control during the performance of a curling stone delivery.

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Francisco Javier Alonso, Publio Pintado and José María Del Castillo

The use of the Hodrick-Prescott (HP) filter is presented as an alternative to the traditional digital filtering and spline smoothing methods currently used in biomechanics. In econometrics, HP filtering is a standard tool used to decompose a macroeconomic time series into a nonstationary trend component and a stationary residual component. The use of the HP filter in the present work is based on reasonable assumptions about the jerk and noise components of the raw displacement signal. Its applicability was tested on 4 kinematic signals with different characteristics. Two are well known signals taken from the literature on biomechanical signal filtering, and the other two were acquired with our own motion capture system. The criterion for the selection of cutoff frequency was based on the power spectral density of the raw displacement signals. The results showed the technique to be well suited to filtering biomechanical displacement signals in order to obtain accurate higher derivatives in a simple and systematic way. Namely, the HP filter and the generalized cross-validated quintic spline (GCVSPL) produce similar RMS errors on the first (0.1063 vs. 0.1024 m/s2) and second (23.76 vs. 23.24 rad/s2) signals. The HP filter performs slightly better than GCVSPL on the third (0.209 vs. 0.236 m/s2) and fourth (1.596 vs. 2.315 m/s2) signals.