In an article reported in the FITNESS & SPORTS REVIEW INTERNATIONAL, Mel C. Siff, Ph.D., professor of mechanics at the University of Witwatersrand in South Africa, brought out that reliance on low impact as the sole form of training may be counterproductive. For example, low impact aerobics, yoga, calinetics, aquarobics and stretch and tone are touted as the ultimate in safe training mainly because they avoid all movements which may produce an impact on contact with any surface.
This may be true under certain circumstances but high impact exercise is not the only way of producing large forces. Prolonged static stretching using even moderate static force can cause deformation of the ligaments, muscle fascia and other connective tissues. What needs to be appreciated is that injury to the body is not necessarily caused by large external forces. The magnitude and direction of the stresses and strains produced by the force are of greater importance than how much force is generated.