Vertical Training - Basic Jump Science

The height of a jump is determined by the velocity of the center of mass as the body leaves the ground. The faster the initial upward velocity, the longer it will take for gravity to decelerate the body and bring it back to earth. The initial velocity is determined by the acceleration of the center of mass due to the force generated by the body, mostly the legs. So if you want to increase your vertical leap, the goal is to increase the force that your legs can generate. Simple enough right? Just lift weights, and your muscles will grow; your legs will be stronger, and you will jump higher. Well, everyone discovers at some point that jump training is not quite that easy.

The truth is that there are three different muscle and nerve qualities that contribute to a jump. (Notice that I mentioned nerves. Many people do not realize the importance of the nervous system in jump training.)The first quality that affects a jump is maximum strength or limit strength; this is the largest amount of force that a muscle can exert. This is the most familiar muscle quality and the most commonly trained. It is increased by common resistance training, which most people are familiar with. The back squat is an example of a resistance training exercise that would help someone jump higher. The second muscle quality is speed of force development, more simply stated as explosiveness. Muscles cannot instantly exert their maximum force; it takes a little bit of time to activate all the muscle fibers. That time is small, just a fraction of a second, but it is still longer than the time it takes to jump, meaning that the maximum force of a muscle cannot be utilized in a jump.

This is the reason for the gap between strength and jumping ability. Consider this scenario... Let's say Timmy weighs 150 pounds and can exert 500 pounds of force on his center of mass (COM) in the range of the jumping motion. As Timmy finishes the countermovement before his jump, his legs are not generating that 500 pounds of force yet. 2/100 of a second after his muscles begin to develop force, his legs are exceeding 150 pounds, and his COM begins to accelerate upwards. At 1/10 of a second, his legs are putting out 215 pounds of force, and his COM is accelerating faster. By 2/10 of a second, the force on his COM has grown to 350 pounds, but unfortunately his legs and back are fully extended; he's done jumping. Timmy never got to use all his force. These force numbers are purely hypothetical, but people really do take right around 2/10 of a second to jump.

The maximum force an athlete's body can exert cannot be generated in that time. The goal for athletes is to train to increase the percentage of their maximum force that can be generated quickly enough for use in jumping and all athletic maneuvers. This ability is improved by exercises that require fast muscle contraction; power lifts (clean, snatch, jerk) and plyometric drills are the most common. Note though, that exercises that use fast movement do very little to increase the strength of the muscle. It is the ability of the nervous system to quickly stimulate muscle fibers that is the focus of this training. The third muscle quality is elastic strength. This is the ability of muscles and tendons to store energy in a stretch and utilize it in the following contraction. This process, called the stretch-shortening cycle, is what causes a higher jump from an approach than from a standstill. The human body naturally uses a countermovement before powerful motions in order to take advantage of this muscle-tendon quality. When you squat down to jump or pull your arm back to throw, you are using elastic strength to add force to the motion. The trick is that the desired motion must immediately follow the stretch to prevent the energy from dissipating. To demonstrate this, perform a natural jump and take note of how high you got. Then do a jump but pause for a second in the crouched position before exploding upward.

This jump should not be as high, because the energy from the drop into the crouched position dissipates during the pause. Elasticity of the muscle-tendon complex is improved by plyometric training and increased flexibility.

Vertical leap training needs to be tailored to the individual strengths and weaknesses of an athlete in the areas that have been mentioned. Therefore, it is incorrect to offer a single program and guarantee a certain result to anybody who tries it. A basketball player who cannot squat his own bodyweight will hardly benefit from a plyometric program, and a bodybuilder who squats twice his bodyweight will experience little gain from adding 20 pounds to his max squat. An effective training system must target all the facets of vertical jumping.



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