... athletes backwards thrust against the earths surface (Carr 1997). The ground reaction force R is equal in action line and magnitude to the downwards thrust of the foot during running but in the opposite direction. The force is greater at the heel strike then at mid stance because of the body's momentum and greater at push-off due to the plantar flexion thrust of the calf muscles driving the body forwards (figure 1) (LeVeau 1992). The force against the earth's surface is at a slight angle as the athlete's centre of gravity is slightly forwards. The law of inertia stated by LeVeau (1992) the body remains at rest until acted upon by an unbalanced force which is proportionate to the body's weight. Most jumpers take a long third last stride which lowers the centre of gravity and by making the last stride relatively short (Figure 2) allows the hips to dip ...

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