All jumps coaches and jumpers should have some understanding of basic bio-mechanical principles. It helps in the learning and understanding of the event.
1. HORIZONTAL VELOCITY
Theoretically this would mean that the greater the sprint speed we can obtain in the approach run, the greater will be the velocity and therefore the distance. However, we do require height in the air in order to gain the best take-off angle and this means we must have time to produce enough force for some vertical velocity too.
Many younger jumpers are UNABLE to produce this vertical component if they run too fast and produce a low skimming jump, achieving less distance than they would have if they had run more slowly or with a shorter run up.
2. TRANSFER OF VELOCITY
In long jumping, the PLACING of the jumping foot considerably in advance of the centre of gravity does lead to the slowing down of the horizontal velocity. This reactive force is absorbed by the supporting leg, and, if strong enough, is returned as spring, now partly vertical, into the air.
In order that this transition can take place, long jumpers tend to sink down slightly on the last but one stride and tend to gain time for a greater impulse as a result, as well as making the change of direction of the velocity from horizontal to vertical easier to attain.
A PERSONAL OBSERVATION: In my opinion based on coaching jumps for 30 plus years this ‘sinking’ occurs naturally and should not be coached. Having observed and filmed/videoed countless jumpers during this last three strides to the take-off board, this sinking occurs without any great thought from the jumper. The sink is a natural reaction when preparing to channel all the horizontal velocity attained on the runway into a vertical impulse.
3. FORCE APPLIED
The short time that a long jumper has on the board limits his/her ability to develop power. This 0.11-0.13 of a second is ‘all the time’ they have to develop vertical force by extending the support leg and ankles, and in which to create force from a strong thrust-up of the free thigh and the counterbalancing arm.
A long jumper needs fast reactions of the nervous system to impart a vertical impulse in so short a touchdown time.
NOTE: Once a specific drill has been introduced, practiced and understood, any short approach work done from 4-10 strides MUST be done a high speeds. This will have the effect of educating the body’s nervous system to react very quickly in a short period of time.
4. TRANSFER OF MOMENTUM
The parts of the body [arms and legs] can generate momentum [mass x velocity] in a given direction which can be imparted in amount and direction to the body as a whole. For long jumping the time we are in contact with the ground at take-off is so short that we must use faster, shorter levers so we shorten the moment arm by using bent-knee swings and usually bent-arm swings. Short levers are quick and dynamic although a long lever is more powerful but not necessarily quicker.
5. ANGLE OF PROJECTION
The angle on the long jump is a compromise between the need for horizontal velocity and the need for height. The horizontal velocity reduces the time on the board and therefore the time to gain height. In the case of the younger jumper, excessive speed is often the cause of poor jumping because there is little or no time to gain the optimum take-off angle.
We are looking at angles of between 18° and 22°. This angle is measured from the C of G.
6. VERTICAL HEIGHT OF THE CENTRE OF GRAVITY
Theoretically this ought to be at its maximum so that contact with the ground is lost as the C of G passes over the supporting foot. THIS NEVER HAPPENS. The faster the approach the more likely the C of G is to be in front of the support foot and thus lower than it could be.
Of course, a taller jumper has an advantage. All movements which raise limbs at take-off raise the C of G also. So a fully extended and raised lead leg, a high upward thrust of the free thigh and arms well raised up are assisting in this direction.
FOOTNOTE:
I really feel that it is important that a horizontal jumps coach be aware of these basic bio-mechanical concepts. An understanding of them can only enhance the coaching process.
