RESULTS: Linear Kinematics

Joint Position. The linear hip angle in the vertical and horizontal direction remained similar. The backpack movement started at .68 meters and ended at .67 meters, while the frontpack movement started at .81 meters and ended at .82 meters. Due to the movement being recorded on a treadmill, stride length (horizontal displacement) was -.01 meters for the backpack and .01 meters for the frontpack. The vertical displacement of both movements started and ended at the same relative position with minute deviations between them.

Figure 8. Position of the hip angle with a backpack (left) and a frontpack (right). Red lines represent movement in the vertical direction. Increasing values indicate upward movement, while decreasing values indicate downward movement. The blue lines represent movement in the horizontal direction. Increasing horizontal values indicate forward movement, while decreasing horizontal values indicate backward movement.

Joint velocity. The horizontal and vertical velocities did not prove to be much different between the frontpack and the backpack. The horizontal velocity of the backpack was -.01 meters per second, while the horizontal velocity for the frontpack was .01 meters per second. The vertical velocity of the backpack and the frontpack for the entire movement remained constant at zero. The yield phase, had the minimum vertical velocity of -.4 meters per second while the frontpack showed a minimum of -.53 meters per second. The swing phase had the maximum vertical velocity for both movements at .4 meters per second.

Figure 9. Velocity of the hip joint with a backpack (left) and a frontpack (right). Blue lines represent horizontal velocity. Positive values indicate forward motion, while negative values indicate backward motion. Red lines represent vertical velocity. Positive values indicate upward motion, while negative values indicate downward motion.

Center of mass. The torque of the backpack versus the frontpack proved to be significantly different. By multiplying the moment arm by the mass of the pack, the frontpack had 5.67% more torque, then the backpack. The torque produced from the backpack was 449.51 Newtons per centimeter, while the torque produced from the frontpack was 2550.19 Newtons per centimeter. The center of mass for the backpack was located at 2.02 cm from the hip, anterior to the pack and approximately between the subject's backpack and hip. However, the center of mass for the frontpack was located at 11.46cm from the hip, posterior to the pack and approximately between the frontpack and hip. On the second frame of movement, the center of mass for the backpack movement was (71.25cm, 115.99cm), while the center of mass for the frontpack was (69.42cm, 111.71cm).

Figure 10. Location of the center of mass (CM) with a backpack (left) and a frontpack (right). The body has been broken down into the shoulder, back or frontpack, thigh and shank segments