Plyometry is a term often used in the sports world and in sports rehabilitation. But what is it? Plyometric exercises are exercises in which the muscle is first briefly brought to length to create rapid explosive action from this front rack. In short, the muscle first gets longer through stretch and then quickly shortens by tightening. Many movements know this form of muscle actions. Thinking of the forehand movement inside tennis, it collapses before a basketball player jumps up to shoot. A volleyball player who sinks in for the installation of a block first.
Literally plyometry consists of the terms plyo and metrie. Plyo is folding/folds and metry stands for distance. Plyometric movements are also often called jump shapes. However, plyometry can also take place in the upper extremity and is therefore not synonymous with only jumping forms.
The theoretical construct behind plyometry is the Stretch Shortening Cycle (SSC). An SSC is an active stretch (eccentric contraction) of the muscle followed directly by a shortening of that same muscle (concentric contraction). The SSC consists of three phases:
- Eccentric phase = extension of muscle (agonist)
- Depreciation phase = pause between phase 1 and 3 (eccentric-concentric coupling)
- Concentriche phase = shortening of muscle (agonist)
Verkhoshansky has divided plyometry into three different accents. The first group consists of jump forms where the emphasis is on the use of elastic energy using short ground contact times. The second group that can include plyometric exercises are characterized by the ability to time muscle contractions properly and make maximum use of stretch reflex potential. The third category exercises are aimed at the stimulation of the central nervous system. All three categories are different in nature and lead to a different objective.
Category 1 exercises are fast and resilient. Have very short ground contact times (<250ms) and are not necessarily powerful. They correspond to another plyometric format called “fast SSC”. Bite-tap image bounces (pogo jumps) and drop jumps
Category 2 exercises are about the application of force. Repeated, dynamic fluid and light jump shapes are below. For example, horde jumps.
Category 3 exercises are jumps with and without external resistance (e.part of rods) or from height (depth prongs). Examples include (loaded) squat jumps, countermovement jumps, depth jumps (depth jumps). These jump forms are characterized by slower ground contact times (>250ms) and are also called “slow SSC” exercises.
A dichotomy can be made when it comes to landing. In literature there is talk of a “soft” landing and a “stiff” landing. Rehabilitation programs and prevention programs generally use soft landings to reduce vertical peak ground reaction forces. This is also used in programmes for novice and youthful athletes. Especially because these programs are mainly focused on landing mechanics. If the focus is on neuromuscular stiffness, hard landings are better. Coaching terms that are part of this are loud, loud, fast and stiff.
Within coaching plyometry, it is possible to make good use of instructions for motor learning. In both the cognitive phase and the associative phase, external focus cues are very valuable. External focus focuses on the effect of movement. This is based on indications that strengthen the internal focus and are more focused on implementing the movement. Examples of clues aimed at external focus are
- Land stiff and aggressive
- You land on eggs, try not to break them
- You sneak out of the house, don’t let your parents hear it
- The floor is made of glass, bag not through it
Applying plyometry in training and rehabilitation programs can sometimes be complicated. This has to do with the multi-factorial aspect. Think, for example, of aspects such as ground contact time, impact and duration of the Stretch Shortening Cycle (SSC). To better understand the factors you can take into account, you can turn plyometry into a quadrant. The y-axis is the impact of the jump and the x-axis the ground contact time. The intensity of the exercise is the product of the impact and ground contact time. A short ground contact time combined with a high impact gives a high intensity to the exercise. By linking the sports analysis and taking into account the taxability of the athlete, you can apply plyometry progressively.
Depth of Drop Jump?
Depth jumps (depth jumps) and drop jumps are terms that are often used interchangeably. However, they are actually two different exercises.
A drop jump includes minimal knee bending (small flexion moment) during ground contact, shorter ground contact times and is more joint/tendon (ankle) dominant. These types of jumping forms are very burdensome for the connective tissue and will therefore be used mainly for the training of tendon tissue. Strengthening tendon tissue (stiffness) is the main goal.
A depth jump includes a deeper knee angle (wide flexion moment), longer ground contact times and thus more muscle is dominant. In particular, the m. quadriceps is strongly stimulated by these jumping forms.