FLUID FORCES ON THE HANDS AND FOREARMS
The influence of forces created by the hand and forearm were measured by taking plaster casts of four arms and analyzing the force components in the swimming flume. The article itself is somewhat misleading. It develops the impression that lift is more important than drag for propelling swimmers. However, the data suggest exactly the opposite. The following is a reinterpretation of what is revealed.
- Drag is greatest when the hand is pitched at an angle of 50 degrees or more. This means that the position of the hand should be facing more backward than to the side, a factor that is readily recognized by any swimmer who wants to develop propulsive forces.
- Lift is greatest when the hand is pitched at an angle of 50 degrees or less. If this is done when swimming, a feeling of slipping is experienced.
- The propelling surface is improved if the forearm is included. The forearm contributes more to propulsion than the hand if it is used correctly. This means that coaches should cease to refer to "pulling with the hand" because the imagery that it creates is incorrect. It would be more appropriate to refer to the lower arm (forearm + wrist + hand) fixating in the water and the swimmer moving the body past that fixed point. This would direct the swimmer to maximize drag with the largest surface area that can be accommodated by man's anatomy.
- As a swimmer's speed increases, the amount of contribution of the forearm to propelling force increases. Therefore, it is very important that sprinters be taught how to position the lower arm to create the largest drag force possible. [This is usually done by swimming for some time with clenched fists. That focuses on developing force with the forearm and wrist. The most desirable position is essentially one of keeping the forearm position at right angles to the direction of the push in the longitudinal plane. Note, paddles do not teach or train this feature.]
- The coefficients of drag created by the lower arm are very much higher than the coefficients of lift. At 2 m/s drag is five times greater than lift. [This is another nail in the coffin for a Bernoulli interpretation of propulsive forces in swimming. As research is being intensively directed to measuring what happens in swimming, there is little to no support for Bernoullian lift as a major force in propulsion in competitive swimming. If sufficient interest in this controversy is shown by NSW coaches, a future issue of the Bulletin will be devoted to the latest on this topic.]
- As a swimmer's speed increases the turbulent flow around the lower arm increases. This points out the need to "feel" the water. It also illustrates that it is possible to be too strong when pushing against the water. Very strong individuals can "rip" the water and achieve little beneficial result for their efforts. The critical pressure to maximize force without causing diminution in resistance because of excessive force (speed) is one of the discriminating factors between superior and lesser swimmers. The holding of water to apply the maximum force explains why some swimmers are fast through the water but appear to be stroking slow. Usually, if they attempted to rate high or execute a faster pull, their efficiency and speed through the water would decrease.
Implications. The description of pulling actions in all strokes other than breaststroke as being an "S" shaped pull is wrong. That was originally proposed to maximize Bernoullian lift. Since that is not a major force for propulsion, it would seem better to teach athletes to "fix" their lower arms in the water and move past that fixed point. Fixing the forearm does not mean that it does not move. The position and angle of the propelling surface has to change to accommodate the human anatomy. The lower arm has to be constantly repositioned as different muscle groups come into play and the various joints and actions across those joints change to contribute to propulsion. That is the major reason why the propelling surface moves, not because of lift as described by Bernoullian theorists.
[The interpretation of this article is different to that of the original authors. The data presented do not support some of the original interpretations, particularly where comparisons between lift and drag effects are concerned.]
Return to Table of Contents for ICAR 1991-92 Report.