1.
To get up in the air, jumpers exert a force against the earth's surface well in excess of their own body weight. The earth's
reaction force then drives the athletes upward. The more forceful the athlete's thrust against the earth, the greater the
earth's response.
2. Immediately before takeoff, a jumper's center of gravity is lowered, the body tilted backward,
and the athlete's arms and free leg positioned to the rear of the body. Lowering the body pre-stretches the big muscles of
the jumping leg, preparing them for the leg's explosive thrust downward at the earth. Leaning back combines with lowering
the body so the athlete can spend more time over the jumping foot applying force to the earth. Swinging the arms forward and
upward adds to the downward thrust of the athlete's jumping leg against the earth.
3. The path that a jumper's
center of gravity follows during flight is determined by the velocity at which the athlete is propelled upward at takeoff
and the takeoff angle used.
4. When in flight, movement of one part of a jumper's body causes other parts to move
in the opposing direction. In high the jump, this characteristic helps in bar clearance. In the long jump, rotary actions
of the arms and legs are used in flight to counteract the unwanted forward rotation that inevitably occurs when the athlete
takes off. In a volleyball spike, drawing the arm back and arching the body in a counterclockwise direction will cause the
legs to move in a clockwise direction.
