So by now, you all probably know how I feel about plyometrics. Believe it or not, there is actually science that shows plyo can improve running performance and economy. Since I don’t just expect you guys to take my word for it 
I thought I would share what I have found with you.
According to Wikipedia:
Plyometrics is a type of exercise training designed to produce fast, powerful movements, and improve the functions of the nervous system, generally for the purpose of improving performance in sports. Plyometric movements, in which a muscle is loaded and then contracted in rapid sequence, use the strength, elasticity and innervation of muscle and surrounding tissues to jump higher, run faster, throw farther, or hit harder, depending on the desired training goal. Plyometrics is used to increase the speed or force of muscular contractions, providing explosiveness for a variety of sport-specific activities.
The word plyometric is Latin for “measurable increases” (sounds promising to me!) and was first used to train Olympic competitors.
Speed + Strength = Power
Plyometrics can best be described as “explosive-reactive” power training. This type of training involves powerful muscular contractions in response to a rapid stretching of the involved musculature. These powerful contractions are not a pure muscular event; they have an extremely high degree of central nervous system involvement. (Source)
The underlying mechanism of plymometrics is the stretch-shortening cycle (SSC). Basically, there are 2 phases of muscle contraction: the eccentric (lowering) phase, and the concentric (upward) phase. In general, eccentric movement goes with gravity and lengthens the muscle and concentric movement goes against gravity and shortens the muscle. For example, the lowering phase of a push-up is the eccentric phase and the pushing up part of the push up is the concentric phase because you are pushing against gravity. Get it?
An eccentric phase, which is the muscle lengthening under tension, is followed by a concentric phase in which the muscle is shortened. Attaining a pre-stretch of the muscle causes it to be lengthened eccentrically so tension is developed in the muscle, similar to a rubber band. This stored energy created by the tension can be used to help increase the strength of the following concentric contraction. This concentric contraction must immediately follow being stretched or the tension created will dissipate as heat. (Source)
Plyometric Exercises
Squat Jumps: Squatting down to jump and return to a squatting position.
Jump to Box: Using a box or step, stand behind the step and jump onto the box on two feet. Jump back and repeat.
Lateral Box Jumps: Standing on the side of a box or step and jumping up from one side and down onto the other.
Plyo Lunges: From a lunge position, jump up and switch feet to land in a lunge with the other foot forward.
Warning: Plyometrics has been shown to improve speed and power but also has a high risk for injury. You should not design or try a plyometrics program without the supervision of a professional and should always consult a doctor before beginning a new exercise program 
Plyometrics should also be used in conjunction with running specific strength training and you should have a solid base of physical fitness before beginning a plyometric program.
I only perform plyo drills in a group fitness setting because of the risk for injury. I also do not do plyo more than once a week (if that). I enjoy doing plyo because it is hard and never boring. This is the class I occasionally take at 5:45 am and let me tell you, I am awake after 5 minutes of this class. However, I am also sore for the next few days. Eccentric muscle contractions are associated with DOMS (delayed onset muscle soreness) and let me tell you- you will be extremely sore for the next few days after a plyo sesh!
Happy training!
