Standing Board Jump - Weakest Station??

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Qualitative model of a Standard Broad Jump

Preparation to Leap

The aim of the standing broad jump is to jump from a standing position as far as possible. Jumper stands at the starting line with legs shoulder-width apart, swings his arms forward and backward while flexing and extending his knees for 2 to 3 times to gain momentum. By standing shoulder width apart, he maintains a relatively wide base so that he is able to lower his centre of gravity (COG) for better control of the forward thrust upon landing after the jump. Repeated flexion and extension of the knees and swinging of the arms creates an early change in momentum before the jump to propel the body further. He does not raise his heels at this moment, keeping his feet planted to the ground. Repeated plantar flexion at this moment causes too much instability due to the throwing most of his mass out of his body too early and may cause wobbling. He also leans his body forwards, bringing his centre of mass (COM) forward. He looks straight ahead, and not downwards or upwards because the body has a tendency to travel in the direction of the gaze.

The leap

Jumper times the last swing of his arms backwards to synchronize with the flexion of his knees, and throws his arms forwards whilst extending his knees, pushing his toes against the ground forcefully and leaning his upper body forward during the leap off. The explosive force exerted by the muscles overcomes the body’s inertia, generates a high acceleration and impulse to propel forward. Plantar flexion of the ankle joint by the concentric contraction of the calf muscles against the ground generates a strong reaction force of the same magnitude from the ground back to jumper according to Newton’s third law of motion, propelling him forward. Concentric contraction of the quadriceps and glutes muscles creates a great torsional force that extends the knee joint. By throwing his arms forward during the leap, part of his mass is thrown forward causing a greater change in momentum. While in midair, he flexes his hips as much as he could to bring his knees as close to his trunk as possible to gain more distance. Concentric contraction of the quadriceps muscle generates a strong torsional force to flex his hip joint. Jumper continues to keep his head in anatomical position with his gaze straight ahead.

Preparation to land

Gravitational force acting on his COM gradually overcomes the forward propulsive force generated by the muscles, and pulls and accelerates the body downwards. His C.O.M is lowered to near his thighs and knees now.Jumper dorsi-flexes his ankles before landing so that his heel takes the impact of the landing. The calf muscles eccentrically contracts.He extends his knees from a flexed position to in preparation to land. The hamstrings are stretched and eccentrically contracts.Still keeping his head in upright position, he swings his arms backwards as the body launches forwards.

Landing

Looking down where he lands, the jumper lands firmly with two feet flat on the ground in a counter-movement (squatting position.) The impact returned by the ground reaction force overcomes the forward propulsion and reduces velocity to zero.

By flexing his knees, the quadriceps muscle contracts concentrically to absorb the impact, reducing force taken by the knee joint and the spine. The hamstrings and gluteus muscles eccentrically contract to maintain tension that prevents him from falling backwards. His COM and COG is also shifted back and lowered to near his posterior by the squatting position, reducing further forward propulsion that may throw him forward. His calf muscles concentrically contracts to take the impact at the ankle joint.

He extends out his both arms in anticipation to break any further forward force that pushes him and causing him to fall forwards.The distance jumped is measured from the back of his heel to the point at his toes before he jumped.

All pictures from THE SUNDAY TIMES – UNFIT – IPPT then and now. 18^th March 2007