Walking and Gait Analysis
Posted on March 11, 2009
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Human movement is most simply and conveniently attained by walking which relies on being pain free and having good joint and muscle condition. Sufficient muscle power and full ranges of motion of the legs are necessary to have efficient gait. One legs acts as a mechanical support for the bodyweight whilst the other swings forward to take its place and become the supporting leg. The simplest division of gait is into stance and swing phases which describe the position each leg is in the stages of the gait.
The gait cycle is the name given to the process of passing through all the stages of gait until you come back to the starting point. For approximately ten percent of the gait cycle both feet are on the ground, with a single foot stance accounting for forty percent of the time. The swing phases make up the rest of the cycle as the leg comes through to be placed down again. Quicker walking reduces the length of time these phases last until we are running where there is no double support phase with both feet placed down simultaneously.
The leg joints follow a specific and repeatable series of actions during the swing and stance phases with stance made up of five sections in the order of initial contact, loading response, mid stance, terminal stance and preswing. Heel strike is the common name given to initial contact but some people do not heel strike at all or transfer weight to the heel later in the phase. Heel strike allows the leg which is about to weight bear to take the weight but not compromise speed, stability or shock protection.
With one leg supporting the bodyweight the other limb is going through the swing phase. The body moves the centre of support over the foot in what is known as mid stance, the initial part of the phase of single leg support. Terminal stance occurs next as the heel of the supporting foot rises from the ground and finishes as the other leg makes heel strike and begins to support weight. Preswing is really a preparation for the swing phase and begins with the last part of the both leg support phase, finishing when the foot is raised to begin swing. Foot clearance above the ground and the forward motion of the leg to engage another step are the function of the swing phases of initial, mid and terminal swing phases.
For gait to be efficient it must incorporate some control over the conservation of energy and the absorption of shocks which can be adversely affected by changes in joint motions and the loss of muscle power. This can cause increases in the joint contact forces and lead to musculoskeletal problems with the loaded structures. Bodyweight loads very fast onto the heel strike leg, with 60 percent being transferred within 20 milliseconds of the start of early stance phase.
The leg joints absorb and control these forces as they act as shock absorbers and dampers. When the leg is placed initially on the ground the forward forces involved tend to make the knee bend so we resist this by making the knee straighter even though this increases the forces through the joints. Loading forces are minimised by eccentric muscle action by the hip adductors and quadriceps.
Locomotion demands that we expend energy but for most of us the level is low if we are healthy, going at our normal speed and walking on level ground. We minimise the amount of energy we use in walking by choosing a preferred speed which is most efficient. Musculoskeletal or neurological conditions always slow down the walking speed but do not have to increase the energy load per unit time because patients usually slow their cycle down. However, the energy needed to cover an identified distance can increase greatly with more than three times the normal expenditure in the case of stroke.
Using a wheelchair cuts energy requirements per distance by 50% and allows speed to be maintained. The choice of using a wheelchair may be made by a patient when the amount of energy to get across a certain distance exceeds a certain level, often when the load exceeds 300% of what would be normally required.
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