Takeoff kinematics of axel jumps were determined from a spatial analysis of singles and doubles performed by 16 figure skaters. The takeoff was divided into glide, transition, and pivot phases. During the glide, horizontal speed remained constant, vertical velocity was slightly negative, and over half the angular momentum for flight was generated. In the transition, skaters gained considerable vertical velocity from tangential motion by rotating about the long axis of the blade, Initially this reduced the angle of the support leg with respect to the vertical while the blade ran in the direction of progression. Most skaters continued to gain vertical velocity by angling the blade to the direction of progression (skidding) and rotating up and forward, still about the blade's long axis. There was little angular momentum gain, and forward speed decreased significantly. In the pivot, skaters rocked forward onto the toe picks losing horizontal speed, vertical velocity, and angular momentum.
Wayne J. Albert and Doris I. Miller
Carolyn A. Duncan, Scott N. MacKinnon, and Wayne J. Albert
The purpose of this study was to examine how wave-induced platform motion effects postural stability when handling loads. Twelve participants (9 male, 3 female) performed a sagittal lifting/lowering task with a 10 kg load in different sea conditions off the coast of Halifax, Nova Scotia, Canada. Trunk kinematics and foot center of force were measured using the Lumbar Motion Monitor and F-Scan foot pressure system respectively. During motion conditions, significant decreases in trunk velocities were accompanied by significant increases in individual foot center of pressure velocities. These results suggest that during lifting and lowering loads in moving environments, the reaction to the wave-induced postural disturbance is accompanied by a decrease in performance speed so that the task can be performed more cautiously to optimize stability.
Sarah J. Woodruff, Connie Bothwell-Myers, Maureen Tingley, and Wayne J. Albert
The purpose was to develop an index of walking performance and to examine gait pattern classifications of children with developmental coordination disorder (DCD). The San Diego database (Sutherland, Olshen, Biden, & Wyatt, 1988) provided data for our calculation of the index and for determining that the index was able to differentiate between gait variables of older (ages 3 to 7) and younger (ages 1 to 2.5) children comprising the database. We obtained cinematographical data on 17 biomechanical markers of 6 boys and 1 girl, ages 6 to 7, with DCD, during walking. Analysis of individuals with DCD gait patterns revealed that most had abnormal walking patterns. The means of the time/distance gait variables did not differ between children with DCD and San Diego children, ages 3 to 7. Children with DCD had much larger variances than other children, indicating no systematic pattern in individual gait differences.
Michael W. Holmes, Scott N. MacKinnon, Julie Matthews, Wayne J. Albert, and Steven Mills
Seafaring occupations have been shown to place operators at an increased risk for injury. The purpose of this study was to understand better the demands of a moving environment on the ability of a person to perform specific lifting tasks. Subjects lifted a 15-kg load under four different lifting conditions. A 6-degree-of-freedom ship motion simulator imposed repeatable deck motions under foot while subjects executed the lifting tasks. Subjects were oriented in three different positions on the simulator floor to inflict different motion profiles. Electromyographic records of four muscles were collected bilaterally, and thoracolumbar kinematics were measured. A repeated-measures ANOVA was employed to assess trunk motions and muscle activities across lifting and motion conditions. The erector spinae muscles showed a trend toward significant differences for motion effects. Maximal sagittal velocities were significantly smaller for all motion states in comparison with the stable condition (p ≤ .01), whereas maximum twisting and lateral bending velocities were higher (p ≤ .05). Results suggest working in a moving environment will likely increase the operator’s risk for overexertion injuries, particularly to the trunk region.