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  • Author: John W. Chow x
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John W. Chow

This paper describes a panning videographic technique for measuring stride lengths and horizontal velocities of strides over an entire hurdle race. The technique requires that tapes of alternate black and white sections be placed at the inside border of the inside lane and the outside border of the outside lane of a track as spatial reference and that a vertical reference be videotaped when it is erected at different locations within the track. The stride lengths and horizontal velocities obtained with the panning technique were compared with the corresponding values that were obtained with conventional stationary camera techniques. The results indicate that if three panning cameras are used to cover the entire hurdle race, the average absolute errors in stride length and horizontal velocity are 0.07 m and 0.15 m/s, respectively. Such errors are considered acceptable for some applications. Certain properties of the panning technique are discussed.

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John W. Chow

The purposes of this study were to develop a cinematographic technique to obtain selected parameters over an entire 100-m ran and to evaluate selected characteristics of the maximum speed phase (MSP) and the final phase (FP) for female high school runners. The MSP was defined as the part of the 100-m run consisting of the five consecutive strides which together have the largest average speed value, and the FP as the last 10 m of the 100-m run. Twelve sprinters with best 100-m times from 12.3 to 13.4 s served as subjects. The major findings of this study were that (a) maximum speeds of 8.0-8.4 m/s were reached 23-37 m from the start, (b) an average of 7.3% of the maximum speed was lost by the FP, (c) no significant difference was found between the average stride lengths during the MSP and the FP, (d) the average stride frequency during the FP was equal to 93% of the corresponding value during the MSP, and (e) the decrease in average speed from the MSP to the FP was associated with an increase in support time from the MSP to the FP.

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John W. Chow, Warren G. Darling and James C. Ehrhardt

The purpose of this study was to determine the coordinates of the origin and insertion, muscle volumes, lengths, lines of action, and effective moment arm of the quadriceps muscles in vivo using magnetic resonance imaging (MRI) and radiography for a pilot study involving musculoskeletal modeling. Two magnetic resonance scans were performed, and axial images were obtained for the left thigh of a female subject in the anatomical position to measure muscle volume, coordinates of the origin and insertion, and muscle belly length at the anatomical position of each quadriceps muscle. Six knee radiographs were used to determine the effective moment arm of the quadriceps force at different knee flexion angles. A combination of MRI and radiography data was used to compute the muscle lengths at different knee flexion angles. The coordinates of the vastus lateralis, muscle volumes of individual quadriceps muscles, and effective moment arms were clearly different from the corresponding values from cadaver data reported in the literature. These comparisons demonstrate the advantages of using personalized muscle parameters instead of those collected from cadavers and dry-bone specimens.

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John W. Chow, Warren G. Darling and James C. Ehrhardt

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.

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Mark D. Tillman and John W. Chow

Column-editor : Thomas W. Kaminski

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Mark D. Tillman, Chris J. Hass, John W. Chow and Denis Brunt

During ballistic locomotion and landing activities, the lower extremity joints must function synchronously to dissipate the impact. The coupling of subtalar motion to tibial and knee rotation has been hypothesized to depend on the dynamic requirements of the task. This study was undertaken to look for differences in the coupling of 3-D foot and knee motions during walking, jogging, and landing from a jump. Twenty recreationally active young women with normal foot alignment (as assessed by a licensed physical therapist) were videotaped with high-speed cameras (250 Hz) during walking, jogging, hopping, and jumping trials. Coupling coefficients were compared among the four activities. The ratio of eversion to tibial rotation increased from the locomotion to the landing trials, indicating that with the increased loading demands of the activity, the requirements of foot motion increased. However, this increased motion was not proportionately translated into rotation of the tibia through the subtalar joint. Furthermore, the ratio of knee flexion to knee internal rotation increased significantly from the walking to landing trials. Together these findings suggest that femoral rotation may compensate for the increase in tibial rotation as the force-dissipating demands of the task increase. The relative unbalance among the magnitude of foot, tibial, and knee rotations observed with increasing task demands may have direct implications on clinical treatments aimed at reducing knee motion via controlling motion at the foot during landing tasks.

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Dali Xu, John W. Chow and Y. Tai Wang

This study examined lower extremity joint moments during walk and turn with different turn angles and pivot feet. Seven young adults (age 21 ± 1.3 yrs) were asked to walk at a self-selected speed (1.35 ± 0.15 m/s) and to turn to the right using right (spin turn) and left (step turn) pivot feet at turn angles of 0° (walking straight), 45°, and 90°. Video and forceplate systems were employed for kinematic and kinetic data collection. Inverse dynamics approach was used to compute joint moments using segmental kinematics, ground reaction forces, and moments. The participants decreased their forward speed by increasing the ankle plantar flexion moment as the turn angle increased. The peak ankle plantar flexion moment during the braking phase increased with increasing turn angle for both spin and step turns. Ankle invertor moments were observed only in spin turns, suggesting that more ankle muscles are involved in spin turns than in step turns. The turn angle had a significant effect on the transverse plane moment profiles at the different lower extremity joints. The results suggest that the loading patterns of different anatomical structures in the lower extremity are affected by both turn angle and pivot foot during walk and turn actions.

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John W. Chow, Warren G. Darling, James G. Hay and James G. Andrews

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.

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Chris J. Hass, Elizabeth A. Schick, John W. Chow, Mark D. Tillman, Denis Brunt and James H. Cauraugh

Epidemiological evidence suggests the incidence of injury in female athletes is greater after the onset of puberty and that landing from a jump is a common mechanism of knee injury. This investigation compared lower extremity joint kinematics and joint resultant forces and moments during three types of stride jump (stride jump followed by a static landing; a ballistic vertical jump; and a ballistic lateral jump) between pre- and postpubescent recreational athletes to provide some insight into the increased incidence of injury. Sixteen recreationally active postpubescent women (ages 18–25 years) and 16 recreationally active prepubescent girls (ages 8–11 years) participated in this study. High speed 3D videography and force plate data were used to record each jumper’s performance of the stride jumps, and an inverse dynamic procedure was used to estimate lower extremity joint resultant forces and moments and power. These dependent variables were submitted to a 2 × 3 (Maturation Level × Landing Sequence) MANOVA with repeated measures on the last factor. The findings indicated that postpubescents landed with the knee more extended (4.4°) and had greater extension moments (approximately 30% greater hip and knee extension moments) and powers (40% greater knee power). Further, the post-pubescent athletes had greater knee anterior/posterior forces as well as medio-lateral resultant forces. The differences found between the two groups suggest there may be anatomical and physiological changes with puberty that lead to differences in strength or neuromuscular control which influence the dynamic restraint system in these recreational athletes. A combination of these factors likely plays a role in the increased risk of injury in postpubescent females.