An evidenced-based approach to plyometric training
The use of plyometric training was previously only seen within strength and conditioning and sport science practice. However, the programming of plyometric training is now common within many different areas, with plyometric boxes becoming a staple piece of equipment within performance and commercial gyms alike. Unfortunately, many see such equipment as an opportunity to demonstrate a maximal box jump, before sharing this feet on social media, without realising that what is really being demonstrated is hip flexion/squat depth capabilities whilst landing on a high box’ rather than actual hip height displacement. What I find more impressive, is an athlete that can perform a high box jump, and still land with the same degree of knee flexion as previously demonstrated on a box jump of a lower height. Hence, a true expression of vertical jump performance.
Another personal bugbear is the programming of plyometrics within an aerobic-based fashion, with individuals performing box jumps over an extended period, and an accompanying drop ineffective landing performance, poor mechanics, knee valgus, no ankle stiffness, and a general biomechanical car crash. So how should plyometrics be used, and what variables should coaches consider when programming plyometrics?
Matching the kinetics of the sport
The great Yuri Verkhoshansky first proposed the use of the ‘shock method’ to improve jumping performance in long jump and triple jump track and field athletes, with the term ‘plyometric training’ later being introduced within the west. Verkhoshansky early work involved the experimentation of depth jumps from varying heights (up to 3m) whilst recording the corresponding ground reaction forces (GRF) using force platform technology, with the aim of replicating the sort of GRF experienced by track and field athletes at the point of take-off. Hence, the purpose of the applied depth jumps was to improve jump performance by regularly subjecting athletes to the kinetic (GRF) demands of their chosen track and field jump based sports, thereby creating the right conditions for specific jump performance related adaptations to occur (e.g. increased muscle stiffness, reduced amortisation time, enhanced muscle spindle function and stretch reflex capabilities, etc.).
Therefore, when programming plyometrics, coaches should consider the kinetics of the movement that they are trying to enhance, and look to match the kinetics (types of GRF) within the programmed plyometrics, rather than solely aiming to match the kinematics of the same movement (joint angles, joint displacement – essentially what the movement looks like). One way this can be done is to consider how long the force is being applied for during the actual ground contact time (impulse) and categorise plyometrics into short or long contact time groups (e.g. pogo jumps or ankling vs squat jumps). For example, during maximal speed running, short contact time plyometrics would more specifically mimic the ground contact times that occur whilst sprinting at top speeds, whereas long contact time plyometrics would be more suited to the acceleration phase of a sprint, as ground contact time is greater due to the need to overcome inertia. Likewise, the playing surface of an athletes chosen sport should also be considered when selecting short or long contact time plyometrics. For example, an athlete that plays on a soft surface may benefit more from long contact time-based plyometrics that focuses on absorbing force, whereas an athlete who competes on a hard court may benefit more from short contact time, elastic/recoil based plyometrics. Therefore, when programming plyometrics, coaches should consider the kinetics associated with the movement that is being enhanced, and the playing surface during the actual competition, and replicate this accordingly. For more information on plyometric training, look out for effective plyometric programming part two, and remember, base plyometrics training on the sport, and not your ego!
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