Technique > Step Anatomy > STANCE PHASE - CONTACT SUBPHASE
In animations below, the blue
leg is in stance phase and the
green leg is in swing phase.
 
 

Frames with grey background
indicate those being
discussed on this page.
 
 

Frames being discussed--
shown in slower motion.
 
 
The Contact subphase is a period of time at the beginning of the stance phase. It beings when the swing leg makes initial contact with the ground (usually on the heel)--thereby becoming the stance leg. It ends just before the foot of the stance leg flattens on the ground--when the heel and toes of the stance leg are on the ground. Its main purposes are to keep the body from falling too far forward, to maintain (or, at least, not significantly diminish) forward momentum, and to establish the essential foundations of the stance phase.
 
PROPULSION
 
Several factors affect how much (if any) net propulsive force is generated during the Contact subphase. The net effect of all force factors is, at best, a relatively weak propulsive force. A failure in technique, however, can easily cause more braking than propulsion.
 
Torque: Upon initial contact with the ground, torque is already being applied to the stance leg as it is brought up to the speed of the ground passing beneath it. At contact, the friction between the shoe and the ground translates that torque into a propulsive force which continues throughout the Contact subphase.
 
Falling: Upon initial contact with the ground, the stance leg quickly stops the falling force generated during the preceding swing phase. Then, while the stance foot is in front of the body's center of mass, the stance hip will start riding up and over the straight stance leg. Until the stance leg passes under the center of mass, the falling force (caused by gravity) will be encouraging the body to fall backward--especially if the walker has overstrided. After passing under the center of mass, the falling force will begin encouraging the body to fall forward--though the foot may have flattened by that point and the walker would be in the Mid-Stance subphase.
 
Pushing: There should be no pushing force exerted during the Contact subphase. Because the knee is already straight and straightening the knee is therefore not an option, pushing is accomplished by the forefoot--which, by definition, has not yet landed during this subphase.
 
Miscellaneous: (a.) If the new stance foot was moving aft faster or slower than the ground when the foot made first contact, a momentary acceleration or braking force might be applied. (b.) If the new stance leg made contact with a bent knee, the pressure exerted by the front muscles of the upper leg might easily generate a braking force as they try to keep the knee from bending farther.
 
BIOMECHANICS OF THE HIPS
 
hip rotation: The stance-side hip will begin this subphase either at its most-forward position, after just having begun its movement aft. The actual location will depend on the walker's ability to make initial contact just as the heel reachs its forward-most position during the gait cycle. The hip will then continue to move aft throughout the subphase.
 
hip drop: The stance-side hip will begin the subphase at or below median height. Race walkers are encouraged to make initial contact with their toes held high, and to hold them up for as long as practical. Because most people can not raise the angle of the bottom of a foot much more than a few degrees above a right angle with the leg, some walkers keep the stance-side hip low at the point of first contact to increase the angle of the stance leg--thereby increasing the angle of the foot. In doing so, however, the walker must be sure to effectively use the hips to compensate for the higher climb that must be made by the stance-side hip in order to avoid a significant increase in the pressure exerted by gravity to fall backward during the climb.
 
BIOMECHANICS OF THE LOWER BODY
 
straightened knee: The upper and lower parts of the swing leg should have reached the same angular speed moving aft as the knee straightened just prior to, or as, the initial contact was being made by the stance leg with the ground. If the lower leg did not reverse course and catch up to the aft-moving upper leg in time, the knee is bent on contact and one of two things will probably occur (both of which are not desired): (a.) the knee will straighten too late and, possibly, cause a jarring action that can hurt the knee over time; or (b.) the knee will not straighten at all. In either case, a creeping call can be anticipated from one or more judges.
 
flexion of the quads: If the knee is straightened on first contact, and the walker is confident of such straightening, the muscles at the front of the upper part of the swing leg (the quads) will be relaxed during the Contact subphase. If the knee has not straightened in time, the pressure exerted on the knee to bend further (due primarily by the falling force generated during the swing phase) will make it extremely difficult--if not impossible--for the quads to force the knee into a straightened position at this time. As they try to straighten the knee, or at least keep the knee from bending further, the quads tighten (flex) significantly.
 
Gary Westerfied [see Note 1] argues that the flexed quads are often clearly visible to a judge and should be used as a flag to pay more attention to such a walker. Flexed quads, however, do not always indicate creeping. If the knee is straightened on landing but the walker is not confident of such straightening, the walker may intentionallly tighten the quads at this time to help insure a straightened position. He is legal but he is wasting a lot of energy, attracting unnecessary attention by the judges, and running the risk of hurting his knee by "popping" it into a locked position.
 
holding the toes up: Ideally, the walker has made initial contact with the forefoot off the ground, and keeps the toes up while he rolls the foot to the flattened position. For many, if not most, top-flite race walkers, the foot does not flatten until the stance foot is about to pass under the body's center of mass. The reason for holding the toes aloft as long as possible is that more surface area of the shoe touching the ground means more energy is lost due to the compression and expansion of more sole and inner-sole material. The energy loss translates into a negative propulsive force.
 
BIOMECHANICS OF THE UPPER BODY
 
The shoulders and arms generally track the hips and legs on the opposite side of the body--the swing-side upper body tracking the stance hip and leg, and the stance-side upper body tracking the swing hip and leg.
 
shoulders: If shoulder rotation is used, the shoulders enter this subphase having just reversed direction and are starting their journey from front to rear or vice versa. If shoulder drop is used, the shoulders generally begin this subphase at their highest position, and are starting to drop down.
 
elbows: If the elbows change angle during the gait cycle, the elbow in front of the body is probably at its smallest angle (bent the most) at this time.
 
arms and hands: If an aggressive arm swing is being used, the aft hand is well behind the midline of the torso and starting to move forward, and the forward hand is well in front of the body and starting to move aft. If the arms are swung at an angle from the line of motion (i.e., inward at the front of the body), and/or the elbows change angle during the gait cycle, the hand in front of the body is often very close to the upper chest at this point.
 
OTHER BIOMECHANICAL ITEMS
 
"sachet": If shoulder rotation is used, the shoulders enter this subphase having just reversed direction and are starting their journey from front to rear or vice versa. If shoulder drop is used, the shoulders generally begin this subphase at their highest position, and are starting to drop down.
 
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[Note 1] See Westerfield's paper on the Use of Biomechanics in the Judging of Race Walking.
 

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