The effect of unsteady flow due to acceleration on hydrodynamic forces acting on the hand in swimming.

This study describes the effect of hand acceleration on hydrodynamic forces acting on the human hand in angular and general motions with variable hand accelerations. Even if accelerations of a swimmer's hand are believed to have an important role in generating hydrodynamic forces on the hand, the effect of accelerations in angular and general motions on hydrodynamic forces on the swimmers hand has not been previously quantified. Understanding how hand acceleration influences force generation can provide useful information to enhance swimming performance. A hand-forearm model attached to a tri-axial load cell was constructed to measure hydrodynamic forces acting only on the hand when the model was rotated and accelerated in a swimming flume. The effect of acceleration on hydrodynamic forces on the hand was described by comparing the difference between accelerating and non-accelerating hands in different flow conditions. Hydrodynamic forces on the accelerating hand varied between 1.9 and 10 times greater than for the non-accelerating hand in angular motion and varied between 1.7 and 25 times greater than for the non-accelerating hand in general motion. These large increases occurred not only during positive acceleration phases but also during negative acceleration phases, and may be due to the added mass effect and a vortex formed on the dorsal side of the hand. This study provides new evidence for enhanced stroke techniques in swimming to generate increased propulsion by changing hand velocity during a stroke.