This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
In walking, the body never entirely quits the ground, the heel of the advanced foot reaching this before the toe of the rear foot has been raised from it. In each step the advanced leg supports the body, and the foot behind at the beginning of the step propels it.
A little attention will enable any one to analyze the act of walking for himself. Stand with the heels together and take a step, commencing with the left foot. The whole body is at first inclined forwards, the movement taking place mainly at the ankle joints. This throws the centre of gravity in front of the base formed by the feet, and a fall would result were not the left foot simultaneously raised by bending the knee a little, and swung forwards, the toes just clear of the ground and the sole nearly parallel to it. When the step is completed the left knee is straightened and the foot placed on the ground, the heel touching first; the base is thus extended in the direction of the stride and the fall prevented. Meanwhile the right leg is kept straight but inclined forwards, carrying the trunk during the step while the left foot is off the ground; at the same time the right foot is raised, commencing with the heel; when the step of the left leg is completed only the great toe of the right is in contact with the support. With this toe a push is given which sends the body swinging forward, supported on the left leg, which now in turn is kept rigid except at the ankle joint; the right knee is immediately afterwards bent and that leg swings forwards, its foot just clear of the ground, as the left did before. The body meanwhile is supported on the left leg alone. When the right leg completes its step its knee is straightened and the foot thus brought, heel first, on the ground ; while it is swinging forwards the left foot is gradually raised, and at the end of the step its great toe alone is on the ground ; with this a push is given as before with that of the right foot, and the left leg then swings forward to make the next step. Walking may, in fact, be briefly described as the act of continually falling forwards and preventing the completion of the fall by thrusting out a leg to meet the ground in front.
Is the body ever off the ground in walking? Describe the act of walking.
During each step the body sways a little from side to side, as it is alternately borne by the right and left legs. It also sways up and down a little ; a man standing with his heels together is taller than when one foot is advanced, just as a pair of compasses held erect on its points is higher when its legs are together than when they straddled apart; in that period of each step when the advancing trunk is balanced vertically over one leg, the walker's trunk is more elevated than when the front foot also is on the ground. Women, accordingly, often find that a dress which clears the ground when they are standing sweeps the pavement when they walk.
The length of each step is primarily dependent on the length of the legs, though it can be largely controlled by special muscular effort, as we see in a regiment of soldiers, all of whom have been taught to take the same stride, no matter how their legs vary in length. In natural easy walking, little muscular effort is employed to carry the rear leg forward after it has given its push; it swings on like a pendulum once its foot is raised from the ground. As short pendulums swing faster than long ones the natural step of short-legged people is quicker than that of long-legged.
At what part of a step is a man tallest? Give illustrations. What primarily determines the length of a person's step? Can this length be controlled ? Illustrate.
Running differs from walking in several respects. There is a moment when both feet are off the ground ; the toes alone come in contact with it at each step ; and the knee joint is not straight at the end of the step. In running, when the rear foot is to leave the ground the knee is suddenly straightened, and the ankle-joint extended so as to push the toes forcibly on the support and powerfully impel the whole body forwards and upwards. The knee is then considerably flexed and the foot raised some way from the ground, and this occurs before the toes of the front foot reach the support. The raised leg in each step is forcibly drawn forward by its muscles and not allowed to swing passively as in quiet walking. This increases the rate at which the steps follow one another, and the stride is increased by the sort of one-legged jump that occurs through the jerk given by the straightening knee of the rear leg, just before it leaves the ground.