At the conclusion of this chapter, the student should be able
- 1. Name those factors that contribute to the propulsion
of a swimmer.
- 2. Name those factors that impede the progress of a swimmer.
- 3. Explain how the propulsive and resistive factors named
affect the length or frequency of a swimming stroke.
- 4. Complete a kinesiological analysis of a swimming stroke
by identifying the anatomical and mechanical factors important to
success in the selected stroke, as well as those factors that appear to
limit the particular performance.
The problem of moving the body through water is fundamentally
not so different from that of moving it on land. As in walking,
it is necessary to push against something to move the body from one
place to another. The chief differences between locomotion in the
water and locomotion on land are that (1) in the water the body
is concerned with buoyancy rather than with the force of gravity,
(2) the substance against which it pushes affords less resistance
to the push, (3) the medium through which it moves affords more
resistance to the body, and (4) as a means of getting the greatest
benefit from the buoyancy and of reducing the resistance afforded
by the water, it is customary to maintain a horizontal, rather than
a vertical, position. (Review the discussion of buoyancy in Buoyancy.) The practical problem in swimming is not to keep
from sinking, as novices are inclined to believe, but to get the
mouth out of the water at rhythmic intervals in order to permit
regular breathing. This is a matter of coordination, not buoyancy.
In swimming, as in all motion, the initial mechanical problem
is to overcome the inertia of the body. Once the body is in motion,
the problem is to overcome the forces that tend to hinder it. In terrestrial
locomotion the body exerts its force against the supporting surface,
the ground, to overcome inertia. The forces resisting the progress
of the body are the forces of gravity and air resistance. In aquatic
locomotion the water is both the supporting medium and the source
of resistance. In swimming the hands and feet depend on the reaction
force of the water in order that the force may be transmitted to
the body. At the same time, the body must overcome the resistance
afforded by the water.
The speed obtained in swimming any stroke
depends on the stroke length and stroke frequency. The length
of the stroke is the result of the forces that move the swimmer
forward in reaction to the movements of the arms and legs, and of
the resistance of the water in the opposite direction. In the front
crawl the arms are the primary source of power, whereas in the breaststroke
the legs dominate. Regardless of the stroke, the actions of the
arms and legs appear to result in a combination of lift and drag