In studying walks it's helpful to think about the weight shift from foot to foot. The videos below show a variety of walks in which this weight shift is measured using force plates (which are essentially digital bathroom scales). Each video shows a sequence of walks with the force on each of the three force plates displayed on the screen behind the person. The equipment has about a quarter-second delay so the data on the screen is delayed by about 5 to 6 frames (i.e., the graph of the forces indicates the first step about 5 to 6 frames after the person's foot touches the first plate).

Normal Walks

The first video shows a series of normal walks by various persons:

[View or Download as Quicktime Movie]

In each case the graph of the weight on the ground exerted by each foot as the person walks across the three force plates looks something like this:

Breaking down the motion we see two distinct elements in the way that weight is transferred from one foot to the other. First, the weight on the back foot is peaked at the moment when the heel of the front foot touches the ground. Then moments later, the weight on the front foot is peaked right when the back foot leaves the ground. This indicates that the "squash" of the body is largest at those two moments.

Second, in the middle of the passing position the weight on the planted leg dips to a minimum; this weight is actually less than the person's weight when standing stationary on one foot, typically by 10%-20%.

The reason that the weight decreases is that the body rises upward then downward during the passing position, swinging like an inverted pendulum. In the same way that you feel light at the top of a moving ferris wheel, due to the centripetal force required to move your body in a small arc during the passing position causes your weight to be lower. This effect is noticable in secondary actions, especially if a character has long hair or loose fitting clothes.

Slow and Fast Walks

This video shows a series of slow walks, such as when sad or tired.

[View or Download as Quicktime movie]

The slow walk differs from the normal walk in that the weight on the planted leg during the passing position is nearly constant. Unlike the normal walk, in the slow walk there are no peaks or dip in the force but rather a smooth transfer of weight from foot to foot. The weight almost always entirely on one foot or the other. For this reason there will be very little up-and-down secondary action or follow-through (e.g., a big belly won't bounce up and down as much in a slow walk as it does in a normal or fast walk).

Now let's look at some fast, brisk walks in the next video:

[View or Download as Quicktime movie]

In a fast walk the highs and lows of the force are greater than in the normal walk; the weight on the planted foot varies by 50% or more. These variation in the weight are particularly large when the arms are swinging up and down. The weight dips in the middle of the passing position when the arms are at their lowest point and rises to a peak in the stride as the arms are rising. This added force against the ground as the arms go up is similar to the added push that's created when you swing your arms as part of a vertical jump.

Notes

Inexpensive force plates are available from Vernier Software and Technology.

Force plate measurements of standing, walking, running, and jumping are discussed in this excellent article:

American Journal of Physics, Vol. 67, pg. 304 (1999).