The J-Curve and Physical Forces

The geometry of the hybrid approach

The modern high jump, dominated by the Fosbury Flop style, is distinguished from other jumps by its nonlinear approach stroke. We use what is known as a "J-Curve".

This hybrid trajectory combines two phases with distinct biomechanical purposes. The first part is a straight run (usually 3 to 5 steps) designed to generate pure horizontal speed and pace, similar to a sprint acceleration.

The second part is a sharp curve (4 to 5 steps) leading toward the bar. This transition from straight to curve is the secret of the jump.

The goal is not simply to reach the mat, but to generate physical forces that the athlete could not produce by running in a straight line.

The coach must ensure that the athlete does not "cut" the curve (making it too flat) or start it too early, as it is the integrity of this geometric layout that allows the necessary rotation in the air without conscious muscular effort.

The generation of centrifugal force

The magic of the curve lies in the physics of centrifugal force. When a body moves at speed along a curved path, a force is generated that pushes outward.

To avoid being thrown off tangentially, the jumper must lean toward the inside of the curve. This lean creates an angle between the body and the ground.

The faster the athlete runs and the tighter the curve, the greater the lean required. This lean position stores potential energy.

At takeoff, when the foot is planted and slows the horizontal movement, that centrifugal force is released, acting as a catapult that helps launch the athlete vertically and, crucially, facilitates rotation with his back to the bar.

Without a bend, there is no smooth rotation; the athlete would have to "force" the turn with the shoulders, losing height.

The integrity of the body lean

A frequent technical error is to lean by bending at the waist or lowering the inside shoulder. The coach should insist that the lean be "from the ankle".

The body should behave like a rigid board leaning en bloc toward the center of the imaginary circle of the bend. This aligns the center of mass correctly.

If the athlete breaks at the waist, he loses tension in the lateral chain and, on take-off, his body will collapse toward the bar ins