Jun25
2014

By: admin                Categories: Animation

Running is a gait that is undertaken once walking is no longer an effective or efficient mode of locomotion and can no longer provide the required speed of motion. A running gait has similarities with the walk cycle, sharing some of the distinctive phases and, in the same manner as a walk cycle, a running action can be broken into separate phases for ease of analysis.

Although the run cycle includes the passing position, the stride is replaced by a phase that distinguishes the running gait from a walk cycle. This is the suspended phase. This phase is the point in the run cycle at which the figure has both feet off the ground and is no longer supported by either foot making contact with the ground. The walk cycle is classified as having at any given point within the action at least one of the feet making contact with the ground. Once both feet are no longer in contact with the ground and the figure is in a state of suspension, the gait is classified as a run.

In addition to the passing position and the suspension phases, I include four other phases in the run cycle, breaking down the action into six distinctive parts in total. These are:

–        The push

–        The suspended phase

–        First contact

–        Squash

–        The passing position

–        The extending phase

The role the arms play in the run remains a secondary action to what they do in a walking gait, though the contribution they make to locomotion is perhaps considerably greater in a running action. This is most evident in sprinters, particularly during that period when they first leave the starting blocks. Movement in the arms is far less extreme during a prolonged running action or a jogging action. The arm action makes a contribution to the overall action, but it is perfectly possible to run while keeping the arms at one’s side, though it is rather unnatural. The use of the arms in a run may vary throughout the action and, as already been mentioned, sprinters that accelerate quickly at the beginning of a run demonstrate a greater degree of motion in the arms than they do once they are into their stride.

The rising and falling of a figure during a running action is much more pronounced than in a walk cycle. The rise during the suspension phase is higher, and the squash results in more compression of the leg due to a bend at the knee, locating the figure slightly lower than in a walk.

As with the walk cycle, the nature of the run determines the speed at which the figure is moving. Furthermore, as with the walk cycle, the speed of the run will change with the varying length and frequency of the strides.

To aid our analysis of a running action, I have broken the movement into the key points in the cycle. For our purposes I have limited the keyframes in the illustration to four, though in the phased sequence that follows, where I provide a detailed written description of the actions at the various points of the cycle, I have included two additional phases.

FIG 5.48 Four key positions of a run cycle.

As with the walk cycle, the phase order I present here has no distinct beginning or end. I have started the sequence in the most obvious place (at least it is the most obvious to me): at the moment just before the figure strides forward and both feet leave the ground.

This sequence provides a general guide for a run cycle, but it is clear that many variations will occur in different instances and for different types of figures.

Phase One: The Push

–        The left leg is extended fully backward, the knee straightened and the toes pushing against the ground, providing maximum thrust.

–        The right leg has swung forward and is bent, allowing the foot to clear the ground. The knee extends forward of the rest of the leg.

–        The left arm is thrust forward and bent at the elbow. The forearm is held in front of the body around the horizontal.

–        The right arm is extended backward and heavily flexed. The upper arm is at the horizontal, with the lower arm being held vertical and at a right angle.

–        The body is bent slightly forward of the upright. A rotation in the torso allows for the left shoulder and the right hip to be placed in a forward position.

FIG 5.49 The Run Cycle: Phase one, the push.

–        The left arm is thrust forward and bent at the elbow. The forearm is held in front of the body around the horizontal.

–        The right arm is extended backward and heavily flexed. The upper arm is at the horizontal, with the lower arm being held vertical and at a right angle.

–        The body is bent slightly forward of the upright. A rotation in the torso allows for the left shoulder and the right hip to be placed in a forward position.

Phase Two: The Suspension Phase

–        The left leg remains extended backward; a bend in the knee occurs at this point because the foot has left the ground.

–        The right leg is extended fully forward and begins to straighten for maximum reach in anticipation of the right foot making contact with the ground.

–        The left arm remains held in front of the body; rotation in the shoulder begins to move the upper arm backward to a vertical position.

–        The right arm begins to swing forward due to a rotation at the shoulder. The angle between forearm and upper arm remains the same.

–        The body is unsupported by the ground at this stage of the cycle and has risen to the highest point within the sequence.

FIG 5.50 The Run Cycle: Phase two, the suspension phase.

Phase Three: First Contact

–        The left leg swings forward more quickly; the lower leg increases the flexion action while the knee moves forward to a point just behind the body.

–        The right leg is angled less acutely away from the body. The knee is more or less straightened and the left foot makes contact with the ground.

–        The left arm continues to moves backward, with the elbow and forearm swinging away from the body to allow it to pass the torso.

–        The right arm has been rotated at the shoulder, so the hand is alongside the body, though the angle between upper arm and lower arm remains the same.

–        The body has fallen from its high point and is once again supported by the single leg. Counterrotation of both the hips and the shoulders now occurs.

FIG 5.51 The Run Cycle: Phase three, first contact.

Phase Four: Squash

–        The left leg has swung to a position whereby the knee is located directly below the body. The lower leg is flexed to the maximum at this point.

–        The right leg absorbs the force of the impact with the ground by flexing at the knee. The foot is flat on the ground and directly below the body.

–        The left arm is held next to the body. There is an increase in flexion between the upper and lower arms, with the elbow appearing just behind the body.

–        The right arm continues to swing to a forward position. The hand is located alongside the hip.

–        The body is now supported by a foot directly below the torso. It has reached its lowest point in the cycle as the impact of the contact is absorbed.

FIG 5.52 The Run Cycle: Phase four, squash.

Phase Five: The Passing Position

–        The left leg continues to swing forward, with the knee being located slightly ahead of the body. The knee remains bent and the foot clears the ground.

–        The right leg begins to straighten and thrust backward, providing kinetic power for the run. The foot remains flat on the ground.

–        The left arm now begins to extend backward, with the elbow clearing the line of the body. The upper and lower arms straighten slightly.

–        The right arm begins to swing around the body, with the hand held in front of the torso.

–        The body now begins to move upward from the lowest point in the cycle. The hips and shoulders continue to rotate.

FIG 5.53 The Run Cycle: Phase five, the passing position.

Phase Six: The Extending Phase

–        The left leg swings forward, the knee rises, and the lower leg moves to a more vertical position, with the foot clearing the ground.

–        The right leg continues to move backward, providing thrust as the foot flexes, with the heel rising and the ball of the foot remaining on the ground.

–        The left arm swings backward, the upper arm moving toward the horizontal and the forearm moving toward a more vertical position.

–        The right forearm continues to flex while the hand moves a little higher and across the front of the body.

–        The body continues to rise. The hips and shoulders rotate, with the left shoulder and right hip facing backward, the right shoulder and hip facing forward.

FIG 5.54 The Run Cycle: Phase six, the extending phase.

FIG 5.55 The Run Cycle: The Push, the suspended phase, first contact, squash, passing position, and the extending phase; sagittal plane (side view).

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Excerpt from Action Analysis for Animators by Chris Webster © 2012 Taylor & Francis Group All Rights Reserved.

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