In this article, I will be explaining the basic physiology, mechanisms, and programming considerations involved in plyometric movements, and explain why we do them in the first place. You may already have experience with these movements in your training. Depth jumps, box jumps, medicine ball throws, and hundreds more all fall into this category. As with all of your training, it is important to know the reasons for doing these skills as well as their appropriate timing within your training session.
Plyometric exercises are those which allow a muscle to reach maximal force in the shortest amount of time possible. All of these movements will involve a countermovement, and a cascade of events involving the series elastic component (SEC), stretch reflex, and stretch-shortening cycle (SSC). “Functional movements and athletic success depend on both the proper function of all active muscles and the speed at which these muscular forces are used.” There is one word to describe the previous statement; power. Plyometric training is essential and has been shown to be a driving force behind power development in athletics.
The series elastic component (SEC) of plyometric movements describes a spring-like mechanism that occurs at the musculotendinous junction. When the tendons of a muscle are stretched in an eccentric contraction the SEC lengthens and elastic energy is created and stored. If this stretching of the muscle is immediately followed by a powerful concentric movement, that stored energy is released and multiplies the amount of force delivered by that muscle. If there is no immediate concentric motion, or the eccentric contraction is too long, that elastic energy will be lost as heat from the body.
The stretch reflex is a neurological mechanism that also plays a part in this type of activity. In the stretch reflex, muscle spindles are activated by rapid lengthening of the muscle. This is what happens in the initiation of a plyometric movement. The innate response of this reflex is to protect the joint by increasing the output of the agonist muscle. When this happens, the force of the muscle is increased, and more power is produced.
|The reaction of the muscle when stretched prior to
contracting is not unlike stretching and immediately
releasing a rubber band.
The stretch-shortening cycle (SSC) contains three phases which incorporate the ideas that we just discussed. The first phase is the eccentric phase. In this phase the muscle in question (agonist) is preloaded, which stimulates muscle spindles. This in turn generates the elastic energy needed for whatever movement is being performed. The next phase is the amoritization phase. This is defined as the time between the end of the eccentric phase and the beginning of the concentric phase. This step must be kept short as to not lose the collected energy as heat. Lastly is the concentric phase, where the stored elastic energy is used and the muscle explosively contracts to perform its function. The power generated in this cycle exceeds by far, the amount of power that can be created by contracting the muscle in isolation.
|High skill exercises such as the Olympic
lifts should be performed early in the
training session when not fatigued.
When programming, one should keep a particular concept in mind. The more neurologically complex a skill is, the earlier it should come in the training session. This is a very general statement, and can apply across any number of skills, not just plyometric training. If I am conducting a comprehensive training session that includes plyos, speed, agility, power, strength, conditioning, etc., I almost always program the plyometric movements at the beginning. The thought here is that if a movement is complex, the athlete or operator needs to learn that movement and get repetitions in while their body and mind are fresh. This way, the task can be performed with precision and perfect execution for thousands of reps. Realistically, when the skill is applied in an actual situation, i.e. game, deployment, combat, the circumstances will likely be less than perfect. In these situations your body can act instinctively, and be precise because of all of the quality reps you have taken in training. If you started out with poor quality work due to improper programming and fatigue, you can certainly not expect your body to execute perfectly under duress.
Another reason to program these skills early on is to prevent injury. As described above, plyometric movements are explosive and ballistic in nature. They should not be done in a fatigued state. There is less room for error. Performing single leg bounds, or single leg box hops are complicated enough, before factoring in fatigue. You’re setting yourself up for a very avoidable injury if their timing in the program is incorrect.
Sets and reps may vary depending on the overall goals of the program, and the volume of the work to be done during that day’s training session. The selection of exercises can mimic what you’re doing in the speed session, (recommended) or they can be stand-alone activities. They can be upper or lower body. Reps are usually on the low side, with adequate rest in between. This ensures that each rep can be explosive and precise. The goal is NOT conditioning here, it is developing explosive power, and the stability needed to generate that power. Keep your reps in the 5-8 range for 2-3 sets and then move on.
There are always exceptions. Even as I write this I can hear people asking “but what about this, and but what about that” types of questions. The point is once you have sound knowledge of these concepts, and you can perform basic skills perfectly, you can entertain some other notions out there and experiment with things that catch your interest. I have a good friend that found a Russian training program to help develop vertical jump. The entire program was depth jumps, and heavy back squats (usually greater than 95%) both done in a very calculated and precise manner. It does not necessarily fit the mold as described above, but it did work.
I hope this was able to highlight some key elements of this type of training. Remember that it is entirely possible to train smart, AND hard at the same time.
1. Essentials of Strength and Conditioning, Second Edition, Baechle, Thomas R. and Earle, Roger W, CH. 19, p 427-431, Human Kinetics, 2000, 1994.