KICKING IS NOT A SIGNIFICANT SOURCE OF PROPULSION
Brooks, R. W., Lance, C. C. & Sawhill, J. A. (2000). The biomechanical interaction of lift and propulsion forces during swimming. Medicine and Science in Sports and Exercise, 32(5), Supplement abstract 910.
This investigation studied the generation of vertical lift forces and their effect on horizontal propulsion during freestyle swimming. Trained male collegiate swimmers (N = 4) were tethered through their center of gravity by two cables (one directed vertically, the other horizontally). Four protocols were used: (i) arms only maximizing forward propulsion, (ii) arms only maximizing upward lift, (iii) kick only maximizing forward propulsion, and (iv) kick only maximizing upward lift. Force data from both cables were evaluated for the length of the stroke.
There was a higher correlation (r = .94) between lift and propulsion in protocol 2 than in protocol 1 (r = .84). There was no significant difference in relationships between protocols 3 and 4.
Swimmers generating vertical lift during the arm stroke will realize an insignificant decrease in propulsion, which may be offset by decreases in drag. The kick is less significant as a propulsive mechanism than as a mechanism for lifting the center of gravity and assisting in streamlining.
Implication. Kicking is not a significant source of propulsion. [It should be noted that this investigation used arms and legs in isolation. It is possible that the relationships would change when both are combined. For example, when the arms accentuate vertical lift, the legs might have to reverse their function and reduce the impact of the arms to maintain a streamlined posture.]
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