Question

Look at a model walking on the catwalk. Review the Mechanical Principles of Walking from pp 461-62 in text, then select and summarize FIVE principles and relate each to the model walking the runway.

Pgs 461-462:

Mechanical Principles in Walking
A number of mechanical principles govern the walking gait. A mechanical analysis of walking should include all of these important principles.

1. A body at rest will remain at rest unless acted on by a force. The force for walking is ground reaction force produced by extension of the lower extremity against a resistive surface. Because walking is an alternating pendular motion of the lower extremities, the inertia of the body must be overcome at every step.

2. A body in motion will remain in motion until acted on by a force. Once motion is imparted to the trunk by the backward and downward thrust of the legs, the trunk has a tendency to continue in motion, even beyond the base of support. A brief restraining action of the forward limb serves as a brake on the momentum of the trunk.

3. Translatory movement of a lever is achieved by the repeated alternation of two rotary movements, the lever first turning about one end and then the other. In walking, the lower extremity alternates between rotating about the foot’s point of contact (support phase) and the hip joint (swing phase). When muscles act to stop or start rotation at one end of the lever, power may be transferred to or absorbed from other segments. This power flow is cyclic in walking (Zajac et al., 2003).

4. Force applied diagonally has both horizontal and vertical components. The vertical component of the ground reaction force used in walking serves to counteract the pull of gravity. The horizontal component of this force serves to (a) check forward motion of the trunk during foot strike and (b) produce forward motion in the trunk during heel-off and toe-off.

5. The speed of walking is increased by increasing either the stride length or the stride rate, or both.

6. The speed of the gait is directly related to the magnitude of the pushing force and to the direction of its application. This force is provided by the extensor muscles of the lower extremity, and the direction of the force application is determined by the angle of the lower extremity when the force is being applied.

7. As propulsion of the body is brought about by the backward and downward push of the foot against the supporting surface, the efficiency of locomotion partially depends on the friction and ground reaction force provided by this surface.

8. The efficiency of gait is related to its timing with reference to the length of the limbs. The most efficient gait is one that is so timed as to permit pendular motion of the lower extremities.

9. Walking has been described as an alternating loss and recovery of balance (Steindler, 1973). This being so, a new base of support must be established at every step.

10. Stability of the body is directly related to the size of the base of support. In walking, the lateral distance between the feet is a factor in maintaining lateral stability. Average step width is about 10% of leg length.

Answer 1

1. A body at rest will remain at rest unless acted on by a force. The force for walking is ground reaction force produced by extension of the lower extremity against a resistive surface. Because walking is an alternating pendular motion of the lower extremities, the inertia of the body must be overcome at every step.

2.A body in motion will remain in motion until acted on by a force. Once motion is imparted to the trunk by the backward and downward thrust of the legs, the trunk has a tendency to continue in motion, even beyond the base of support. A brief restraining action of the forward limb serves as a brake on the momentum of the trunk

3.The speed of walking is increased by increasing either the stride length or the stride rate, or both.

4.. As propulsion of the body is brought about by the backward and downward push of the foot against the supporting surface, the efficiency of locomotion partially depends on the friction and ground reaction force provided by this surface.

5.Walking has been described as an alternating loss and recovery of balance Stability of the body is directly related to the size of the base of support. In walking, the lateral distance between the feet is a factor in maintaining lateral stability.