The purpose of this study was to examine the effects of shaft stiffness on puck velocity and resp... more The purpose of this study was to examine the effects of shaft stiffness on puck velocity and response characteristics of carbon ®bre composite ice hockey sticks during a slap shot. Six elite male ice hockey players performed six slap shots with four sticks of different shaft stiffness designated as medium (13 KN m ±1 ), stiff (16 KN m ±1 ), extra (17 KN m ±1 ) and pro stiff (19 KN m ±1 ). These four levels represent the range in stiffness of sticks available to hockey players. The mechanics of the slap shot were evaluated by recording the initial ground reaction forces and stick deformation from high-speed ®lming and puck velocity from a radar gun. Data were analysed using a 3-way repeated measures ANOVA ANOVA for 7 dependent variables: puck velocity, peak Y (front± back) and Z (vertical) forces, times to achieve peak Y and Z forces, peak de¯ection and time to peak de¯ection of the shaft. Results indicated: (1) the stick with lowest shaft stiffness of 13 KN m ±1 produced the highest puck velocity, the greatest amount of shaft de¯ection, the longest time to peak de¯ection and the lowest peak Z forces; (2) the times to obtain peak forces in the Y and Z directions were similar across the levels of shaft stiffness; (3) puck velocity was in¯uenced by the interaction of subject and stiffness and (4) variability in performance measures across subjects was greater than the variability across stiffness. Future studies are needed to address the effects stick construction has on different shots and stick handling skills, as well as to investigate the speci®c in¯uence that skill and strength of the player has on the stick's response.
The purpose of this study was to investigate the extent to which ice hockey facial protectors can... more The purpose of this study was to investigate the extent to which ice hockey facial protectors can decrease overall head acceleration during blunt impacts, as well as to identify whether attenuation differences exist between visors and cages. Commercial models of three cages and three visors were assessed. Blunt impacts were simulated, permitting the measurement of peak accelerations (PA) within the surrogate headform. Results indicated that face protectors, in combination with helmets, substantially reduced PA during blunt impacts within threshold safety limits (below 300g). In general, cages showed lower PA than visors. Differences between models were also observed during repeated impacts and impact site. In conclusion, this study demonstrates that facial protectors function beyond their role in solely preventing facial injuries, complementing the role of the helmet in attenuating head deceleration during impact. Consequently, the utilisation of facial protectors may reduce the severity and incidence of head injuries.
AZ 85006. Instrumenting lumbar spinal segments with transpedicular screws is increasing in popula... more AZ 85006. Instrumenting lumbar spinal segments with transpedicular screws is increasing in popularity. This project was designed to study the overall and local three dimensional (3-D) motion of calf vertebral columns when instrumented with the Cotrel-Dubousset (CD) pedicle screw instrumentation system, both with and without induced disk defects. Lumbar segments of 2,4 and 6 vertebrae were tested, three for each length. The columns were subjected to axial compressive, anterior and lateral eccentric, and torsional loads. The results showed that the CD-instrumented spinal segments were more sensitive to the integrity of the disk in anterior bending and axial compression compared to during torsion and lateral bending. Furthermore, analysis of local motion showed: (1) the main motion usually occured at the superior vertebrae; (2) there was often posterior sliding of segments above and sometimes even below the disk defect during axial compression and anterior bending tests; and (3) interpretations based only on traditional load-displacement curves can be misleading.
The extent to which errors in predicting body segment parameters (SP) influence biomechanical ana... more The extent to which errors in predicting body segment parameters (SP) influence biomechanical analysis of human motion is unclear. Therefore, the current study quantitatively evaluated the differences in SP estimates using literature predictive functions and computed the effect of SP variation on the kinetic output of walking. For a group of 15 young males, significant differences (PB 0.05) were observed between SP estimates for the leg and thigh using the literature predictive functions, with mass and moment of inertial values differing by more than 40%. Using kinematic and ground reaction force data collected for each subject while walking, inverse dynamic analysis was performed iteratively to compute hip forces and moments while simultaneously varying SP values over nine intervals within 940% of a baseline value. SP variations were found to significantly affect (P B 0.05) most of the kinetic estimates produced, particularly those taken during the swing phase. However, the magnitude of these effects was generally less than 1% of body weight. The data from the current study allows researchers to estimate the errors in kinetic measures due to SP variation. The results also indicate that the accuracy of SP prediction should be of concern in biomechanical research particularly for open chain and high acceleration activities. Further study is necessary to identify the importance of SP variation on other motion skills.
Archives of Physical Medicine and Rehabilitation, 1994
Magnetic resonance images from fifteen physically active and asymptomatic male volunteers were co... more Magnetic resonance images from fifteen physically active and asymptomatic male volunteers were collected to present morphometric parameters on the psoas and its moment arms, which are important in the study of spinal mechanics and models for the investigation of low back pain. The mean age of the subjects was 21.5 +/- 1.8 years. Data were obtained from nine vertebral and/or intervertebral levels (L2, L2/L3, L3, L3/L4, L4, L4/L5, L5, L5/S1, S1). In general, the psoas increased in size as it descended the trunk, moving anteriorly and slightly laterally in relation to the vertebral column. Maximum cross-sectional areas for the psoas (M = 16.3cm2) were observed at the L4/L5 level. Right-left symmetry was apparent in the aforementioned dimension, but not with respect to the mediolateral (X) diameter of the muscle. The length of the X moment arm was significantly (p < .05) greater for the right versus the left psoas from L3 to S1, with the length increasing as the psoas descended the trunk. However, this trend was not noted for the anteroposterior (Y) moment arm where observed values remained relatively small throughout the course of the muscle. These results will contribute to the study of low back pain onset and the design of appropriate rehabilitation interventions by providing accurate morphometric parameters for biomechanical models to predict of the loading conditions of the spine in vivo.
Measures about the foot and ankle within footwear are required to assess the full dynamic interac... more Measures about the foot and ankle within footwear are required to assess the full dynamic interaction. To address this, piezo resistive fabric sensors provide accurate pressure measurement that can be applied within the narrow confines of the footwear-to-footlankle interface. An example of this has been shown in studies focusing on ice hockey skate boots during forward skating. Sixteen flexible piezo-resistive sensors (1.2 cm x 1.8 cm x 0.2 cm thick, FSA Verg Inc.,Canada) were taped to discrete anatomical surfaces of the plantar foot, dorsal foot, the posterior aspect of heel and leg, medial aspect of foot, and lateral aspect of the foot. The results showed an increase in pressure during the stance phase of gait at each anatomical surface with a reciprocal decrease in pressure during swing. INTRODUCTION: Few studies have been undertaken that have looked at in boot pressure distribution patterns of the fool at surfaces other than plantar, with the exception of cases involving rotatio...
Ice hockey pucks are rubber projectiles that can carry >180 J of kinetic energy during a slap ... more Ice hockey pucks are rubber projectiles that can carry >180 J of kinetic energy during a slap shot. When striking the temporal region of the skull, pressures capable of fracture can occur. Despite this risk, there is very little research on the topic. In this study, five helmet models, representing various material and shell compositions, were fit to a Hybrid III headform and subjected to puck impact at 24.2 m/s (PI24) and 33 m/s (PI33). The linear and angular kinematics of the headform and dynamic load distribution at the contact site were measured using 9 accelerometers and 25 force sensors. The cumulative strain damage measure (CSDM) was calculated using the SIMon (Simulated Injury Monitor) brain model. Thick‐shelled HDPE helmets using different EPP foams tended to perform similarly, whereas the combination of thin polycarbonate shell and lightweight foam performed poorly, particularly at PI33, for both acceleration‐derived values and CSDM. Helmets with VN liners appeared to e...
The purpose of this study was to determine the effect of cross-slope on gait dynamics. Ten young ... more The purpose of this study was to determine the effect of cross-slope on gait dynamics. Ten young adult males walked barefoot along an inclinable walkway. Ground reaction forces (GRFs), lower-limb joint kinematics, global pelvis orientation, functional leg-length, and joint reaction moments (JRMs) were measured. Statistical analyses revealed differences across limbs (up-slope [US] and down-slope [DS]) and inclinations (level; 0 degrees; and cross-sloped, 6 degrees). Adaptations included increases of nearly 300% in mediolateral GRFs (p < .001), functional shortening the US-limb and elongation of the DS-limb (p < .001), reduced step width (p = .024), asymmetrical changes in sagittal kinematics and JRM, and numerous pronounced coronal plane differences including increased US-hip adduction (and adductor moment) and decreased DS-hip adduction (and adductor moment). Data suggests that modest cross-slopes can induce substantial asymmetrical changes in gait dynamics and may represent a...
The purpose of this study was to examine the effects of shaft stiffness on puck velocity and resp... more The purpose of this study was to examine the effects of shaft stiffness on puck velocity and response characteristics of carbon ®bre composite ice hockey sticks during a slap shot. Six elite male ice hockey players performed six slap shots with four sticks of different shaft stiffness designated as medium (13 KN m ±1 ), stiff (16 KN m ±1 ), extra (17 KN m ±1 ) and pro stiff (19 KN m ±1 ). These four levels represent the range in stiffness of sticks available to hockey players. The mechanics of the slap shot were evaluated by recording the initial ground reaction forces and stick deformation from high-speed ®lming and puck velocity from a radar gun. Data were analysed using a 3-way repeated measures ANOVA ANOVA for 7 dependent variables: puck velocity, peak Y (front± back) and Z (vertical) forces, times to achieve peak Y and Z forces, peak de¯ection and time to peak de¯ection of the shaft. Results indicated: (1) the stick with lowest shaft stiffness of 13 KN m ±1 produced the highest puck velocity, the greatest amount of shaft de¯ection, the longest time to peak de¯ection and the lowest peak Z forces; (2) the times to obtain peak forces in the Y and Z directions were similar across the levels of shaft stiffness; (3) puck velocity was in¯uenced by the interaction of subject and stiffness and (4) variability in performance measures across subjects was greater than the variability across stiffness. Future studies are needed to address the effects stick construction has on different shots and stick handling skills, as well as to investigate the speci®c in¯uence that skill and strength of the player has on the stick's response.
The purpose of this study was to investigate the extent to which ice hockey facial protectors can... more The purpose of this study was to investigate the extent to which ice hockey facial protectors can decrease overall head acceleration during blunt impacts, as well as to identify whether attenuation differences exist between visors and cages. Commercial models of three cages and three visors were assessed. Blunt impacts were simulated, permitting the measurement of peak accelerations (PA) within the surrogate headform. Results indicated that face protectors, in combination with helmets, substantially reduced PA during blunt impacts within threshold safety limits (below 300g). In general, cages showed lower PA than visors. Differences between models were also observed during repeated impacts and impact site. In conclusion, this study demonstrates that facial protectors function beyond their role in solely preventing facial injuries, complementing the role of the helmet in attenuating head deceleration during impact. Consequently, the utilisation of facial protectors may reduce the severity and incidence of head injuries.
AZ 85006. Instrumenting lumbar spinal segments with transpedicular screws is increasing in popula... more AZ 85006. Instrumenting lumbar spinal segments with transpedicular screws is increasing in popularity. This project was designed to study the overall and local three dimensional (3-D) motion of calf vertebral columns when instrumented with the Cotrel-Dubousset (CD) pedicle screw instrumentation system, both with and without induced disk defects. Lumbar segments of 2,4 and 6 vertebrae were tested, three for each length. The columns were subjected to axial compressive, anterior and lateral eccentric, and torsional loads. The results showed that the CD-instrumented spinal segments were more sensitive to the integrity of the disk in anterior bending and axial compression compared to during torsion and lateral bending. Furthermore, analysis of local motion showed: (1) the main motion usually occured at the superior vertebrae; (2) there was often posterior sliding of segments above and sometimes even below the disk defect during axial compression and anterior bending tests; and (3) interpretations based only on traditional load-displacement curves can be misleading.
The extent to which errors in predicting body segment parameters (SP) influence biomechanical ana... more The extent to which errors in predicting body segment parameters (SP) influence biomechanical analysis of human motion is unclear. Therefore, the current study quantitatively evaluated the differences in SP estimates using literature predictive functions and computed the effect of SP variation on the kinetic output of walking. For a group of 15 young males, significant differences (PB 0.05) were observed between SP estimates for the leg and thigh using the literature predictive functions, with mass and moment of inertial values differing by more than 40%. Using kinematic and ground reaction force data collected for each subject while walking, inverse dynamic analysis was performed iteratively to compute hip forces and moments while simultaneously varying SP values over nine intervals within 940% of a baseline value. SP variations were found to significantly affect (P B 0.05) most of the kinetic estimates produced, particularly those taken during the swing phase. However, the magnitude of these effects was generally less than 1% of body weight. The data from the current study allows researchers to estimate the errors in kinetic measures due to SP variation. The results also indicate that the accuracy of SP prediction should be of concern in biomechanical research particularly for open chain and high acceleration activities. Further study is necessary to identify the importance of SP variation on other motion skills.
Archives of Physical Medicine and Rehabilitation, 1994
Magnetic resonance images from fifteen physically active and asymptomatic male volunteers were co... more Magnetic resonance images from fifteen physically active and asymptomatic male volunteers were collected to present morphometric parameters on the psoas and its moment arms, which are important in the study of spinal mechanics and models for the investigation of low back pain. The mean age of the subjects was 21.5 +/- 1.8 years. Data were obtained from nine vertebral and/or intervertebral levels (L2, L2/L3, L3, L3/L4, L4, L4/L5, L5, L5/S1, S1). In general, the psoas increased in size as it descended the trunk, moving anteriorly and slightly laterally in relation to the vertebral column. Maximum cross-sectional areas for the psoas (M = 16.3cm2) were observed at the L4/L5 level. Right-left symmetry was apparent in the aforementioned dimension, but not with respect to the mediolateral (X) diameter of the muscle. The length of the X moment arm was significantly (p &lt; .05) greater for the right versus the left psoas from L3 to S1, with the length increasing as the psoas descended the trunk. However, this trend was not noted for the anteroposterior (Y) moment arm where observed values remained relatively small throughout the course of the muscle. These results will contribute to the study of low back pain onset and the design of appropriate rehabilitation interventions by providing accurate morphometric parameters for biomechanical models to predict of the loading conditions of the spine in vivo.
Measures about the foot and ankle within footwear are required to assess the full dynamic interac... more Measures about the foot and ankle within footwear are required to assess the full dynamic interaction. To address this, piezo resistive fabric sensors provide accurate pressure measurement that can be applied within the narrow confines of the footwear-to-footlankle interface. An example of this has been shown in studies focusing on ice hockey skate boots during forward skating. Sixteen flexible piezo-resistive sensors (1.2 cm x 1.8 cm x 0.2 cm thick, FSA Verg Inc.,Canada) were taped to discrete anatomical surfaces of the plantar foot, dorsal foot, the posterior aspect of heel and leg, medial aspect of foot, and lateral aspect of the foot. The results showed an increase in pressure during the stance phase of gait at each anatomical surface with a reciprocal decrease in pressure during swing. INTRODUCTION: Few studies have been undertaken that have looked at in boot pressure distribution patterns of the fool at surfaces other than plantar, with the exception of cases involving rotatio...
Ice hockey pucks are rubber projectiles that can carry >180 J of kinetic energy during a slap ... more Ice hockey pucks are rubber projectiles that can carry >180 J of kinetic energy during a slap shot. When striking the temporal region of the skull, pressures capable of fracture can occur. Despite this risk, there is very little research on the topic. In this study, five helmet models, representing various material and shell compositions, were fit to a Hybrid III headform and subjected to puck impact at 24.2 m/s (PI24) and 33 m/s (PI33). The linear and angular kinematics of the headform and dynamic load distribution at the contact site were measured using 9 accelerometers and 25 force sensors. The cumulative strain damage measure (CSDM) was calculated using the SIMon (Simulated Injury Monitor) brain model. Thick‐shelled HDPE helmets using different EPP foams tended to perform similarly, whereas the combination of thin polycarbonate shell and lightweight foam performed poorly, particularly at PI33, for both acceleration‐derived values and CSDM. Helmets with VN liners appeared to e...
The purpose of this study was to determine the effect of cross-slope on gait dynamics. Ten young ... more The purpose of this study was to determine the effect of cross-slope on gait dynamics. Ten young adult males walked barefoot along an inclinable walkway. Ground reaction forces (GRFs), lower-limb joint kinematics, global pelvis orientation, functional leg-length, and joint reaction moments (JRMs) were measured. Statistical analyses revealed differences across limbs (up-slope [US] and down-slope [DS]) and inclinations (level; 0 degrees; and cross-sloped, 6 degrees). Adaptations included increases of nearly 300% in mediolateral GRFs (p < .001), functional shortening the US-limb and elongation of the DS-limb (p < .001), reduced step width (p = .024), asymmetrical changes in sagittal kinematics and JRM, and numerous pronounced coronal plane differences including increased US-hip adduction (and adductor moment) and decreased DS-hip adduction (and adductor moment). Data suggests that modest cross-slopes can induce substantial asymmetrical changes in gait dynamics and may represent a...
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Papers by David Pearsall