プール訓練の為の基礎知識

抄録

All substances are composed of molecules. In a solid the number of molecules for a specific volume is greater than that of water. The cohesive force between molecules in a solid is stronger than that of water. The strong cohesive force of molecules in a solid makes a counter force against a shear force. For example it is possible to stand and walk on a floor without falling through it. The cohesive force of water molecules, however, is not so strong and they do not make a counter force against a shear force (in a static condition). This means that water has no resistance according to Newton's third low.
The resistance in water by human movement is as follows;
1) Wave making (Lifting a weight of water to a position of greater potential energy)
2) Skin friction (Adhesive force of molecular attraction of water molecular to the human body)
3) Viscosity (Molecular attraction of molecules of water to each other in a phasic condition)
4) Turbulence (Making of eddies in water and loss of pressure energy)
In water buoyancy assists our movement, however we have to move against resistances (1〜4) that we do not encounter on land. We move in air only against gravity but in water we have to balance against both, gravity and buoyancy. To balance against these two forces, we need to find our metacenter. If we float on the water, we sway around the metacenter point. By changing the position of the metacenter, we have to react and make postural adjustments to keep our balance. We as therapists use the these postural reactions to controll the patient in water.
We can make turbulence in the water which creates a lower water pressure and causes the patient to be drown into the turbulence. Thus we can use the turbulence to assist or to resist the balance or movement of the patient.
This paper is based on the works of J. McMillan.