Joint Position. The linear displacement of the knee joint for ice-skating and in-line skating were almost identical. Horizontal displacement for ice-skating was 7.05 meters while horizontal displacement for in-line skating was 7.72 meters. The horizontal displacement for inline skating ended with a negative value because the subject's knee finished the gait cycle slightly behind the reference marker. Vertical displacement for ice-skating was .23 meters while the vertical displacement for in-line skating was .06 meters. For ice-skating, the maximum displacement in the horizontal direction was 7.24 meters and the minimum displacement in the horizontal direction was .21 meters. The maximum displacement in the vertical direction (disregarding the two points of error that occurred in the first .36 seconds of the gait cycle) was .73 meters while the minimum value in the vertical direction was .41 meters. The maximum and minimum displacements in both the horizontal and vertical directions during in-line skating were very similar to those of ice-skating. During in-line skating the maximum and minimum displacements in the vertical direction were .96 and .69 meters, respectively. In the horizontal direction the maximum and minimum displacements were 7.7 and -.21 meters, respectively.
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Figure 8. Linear displacement of the knee joint in the ice-skating (left) and the inline skating (right). Increasing values represent forward movement in the horizontal direction and upward movement in the vertical direction. The blue line represents the horizontal position and the pink represents the vertical position. | |
Joint velocity. After the first .36 seconds of the ice-skating, the knee joint velocity in ice-skating and in-line skating are very similar. The horizontal velocities for both the ice-skating and in-line skating movements were always negative because throughout the entire movements the subject was gliding from right to left (in the negative direction). Even if the knee joint was moving in the positive direction during the "propulsion" phase, the constant movement of the body in the negative direction caused the overall velocity of the knee joint to be negative. After the first .36 seconds of ice-skating the maximum velocity in the horizontal direction was 7.10 m/s. The maximum velocity of the knee joint during in-line skating was 7.27 m/s. The minimum velocity of the knee joint during ice-skating (1.31 m/s) was also very similar to the minimum velocity of the knee joint during in-line skating (2.73 m/s). The velocities in the vertical direction were also very similar. The maximum and minimum velocities of the knee joint during ice-skating were 2.22 m/s and &endash;2.22 m/s, respectively. The max and min velocities of the knee joint during in-line skating were 2.72 m/s and &endash;2.27 m/s.
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Figure 9. Linear velocity of the knee joint in the ice-skating (left) and the inline skating (right). Positive values represent forward movement in the horizontal direction and upward movement in the vertical direction. The blue line represents the horizontal velocity and the pink line represents vertical velocity | |
Center of mass. The center of mass location for ice-skating is slightly different than the subject's center of mass during in line skating. The center of mass while ice-skating is relative to the trunk segment whereas the in line skating center of mass is relative to the hip joint. The three points we chose to look at for COM were at time 0, 00:00.693, and 00:01.485.
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Figure 10. Location of the center of mass (COM) in the ice-skating (left) and the in-line skating (right). Body segments shown are the upper arm, trunk, thigh, and shank. | |
