Trampoline jumping is a unique movement pattern requiring a unique technique. Unlike other ground-based jumps, trampoline jumping does not experience a countermovement or a stretch-shortening cycle. While there is a wide array of information on how to improve jump height and technique, not all of this can be generalised from ground-based jumps to trampoline jumps. Force absorption, joint mechanics and even movement timing is different.
Ultimately, for maximum jump height, the athlete wants to push the trampoline bed down as far as possible and exert enough force to ensure that their body does not bend against the force of the trampoline(1). Pushing the bed down maximises the elastic potential energy from the trampoline. As the trampoline exerts a high force against the athlete, propelling them upwards, the athlete does not want to crumple against the force, so they must continue to remain rigid and push back against the trampoline for the duration of the contact time.
The natural consequence of jumping is landing. When landing, the body brings a large inertial force which must be absorbed as it come to a stop or recoils the next jump. The absorption of force can generally be seen by the deformation (changing shape) resulting from impact. For example, if you drop a bowling ball onto a crashmat, the crashmat deforms as it absorbs the impact.
When landing on a hard surface, such as the ground, the human body must absorb the impact, as the landing surface will suffer minimal deformation. To minimise injury, it is recommended that the ball of the feet contacts the ground first, then the heel as the ankle, knee and hip joint all bend to shorten the body and absorb the force across a range of joints and muscles. When landing on a trampoline, the trampoline deforms, allowing the body to remain rigid. The trampoline deforms so much, that the body does not need any active force absorption and we can even do the opposite: try to exert force into the trampoline bed to increase the trampoline deformation.
While trying to maximise force, it is recommended that athletes bend their ankles to land heels first on a trampoline(1), with bent knees and hips. Instead of shortening the body upon impact, the athlete hits the trampoline in a pre-shortened state, ready to push the trampoline as soon as they can. This is evident by the high levels of impact on the heel during the trampoline contact phase(2).
The stretch-shortening cycle is the physiological mechanism behind plyometric training methods. Muscles can output more force after a short stretch built into the movement. For example: To maximise jump height, an athlete stands tall, quickly crouches and then jumps immediately afterwards. This crouch, or countermovement, is the stretch before the jump. Without it, the athlete would not be able to jump as high (for example if the athlete was paused in a seated position before jumping). Optimising the stretch shortening cycle is crucial for ground based jumping performance.
Trampoline jumps do not truly have a stretch shortening cycle. While jumping, the athlete initially contacts the trampoline bed while already in the shortest body position. The athlete then pushes the trampoline away, lengthening their body, without any stretch cycle.
A study performed in 2016 analysed the jumping of Chinese trampoline athlete. This study aimed to find the optimal timing to push against the trampoline bed during contact. The study was poorly designed, using only two body segments, meaning that it only accounted for pushing the trampoline by bending the knees (no ankle movement or hip movement). It also only analysed one athlete on one trampoline. Despite the experiment's limitations, some of its findings may still be relevant.
Upon initial contact with the trampoline, an athlete is in a compressed position. By the time the athlete reaches the lowest compression of the trampoline, their body should be straight at the knees and hips. This position allows for maximum depression of the trampoline bed. The study found that an athlete should hold their compressed body position momentarily after initial contact before beginning to extend at the hips and knees. They found that optimally, the bed would take 0.14 seconds to reach maximum depression and that the athlete should begin extending 0.07 seconds after initial contact(3). While these numbers may not generalise to different athletes and different trampolines, there may be some validity in pausing before extending. The pause would make the extension more rapid, allowing for greater depression of the bed. It is also important that the athlete does not finish extending until maximum depression of the bed.
Due to the elastic nature of the trampoline and the desire to attain maximum height, athletes try not to absorb the forces associated with jumping and landing on the trampoline(1). Athletes must develop an extremely high level of strength to keep their bodies rigid during the contact phase of the trampoline jump(1, 3), as any buckling or bending of the body results in force absorption. Athletes actively try to exert more force into the trampoline by landing in a shortened state and extending their limbs as the trampoline bed depresses(1, 2, 3). To do so, athletes seek to optimise the timing and amount of extension in their lower limbs. Further research is needed to establish what is optimal across a range of athletes and trampolines.
1. Farquharson R. THE DEMANDS OF GYMNASTIC TRAMPOLINING FROM TOUCH DOWN TO TAKE OFF: A PHYSICAL PREPARATION PERSPECTIVE. SportEX Medicine. 2012 Jul 1(53).
2. Huang Y, Wu J, Wang L, Gong M, Chen Z. Technology Characteristics of Trampoline Athletes' Plantar Pressure in Doing Basic Movement on Bed. In2011 International Conference on Future Computer Science and Education 2011 Aug 20 (pp. 97-101). IEEE.
3. Chen J, Guo H, Gao Z, An M, Wang X, Chen W. Optimal kicking of a trampolinist. Human movement science. 2016 Aug 1;48:54-61.
