The truth is that the secrets to a strong vertical jump aren’t really secret at all. They are available to anyone with the ability to go to a university library that has a decent collection of exercise physiology journals and do a bit of reading. That’s not a secret in my book. Of course, not all the findings of these journals filter into the local musclehead gym, but they are known. But be wary of secrets, because if it’s "secret" that means it’s likely that the method has not been subjected to rigorous scientific testing, of the sort that appears in Journal of Exercise Physiology or the Journal of Strength and Conditioning Research.
I don’t want you to feel thoroughly cheated though. I promised secrets and dammit, I’m going to tell you a couple, even if they aren’t truly secret. So rather than asking "what is the secret?", let’s ask "what does recent, published, scientific research have to say?" And specifically, does recent scientific research give any guidance with respect to lesser-known training techniques that would really benefit someone looking to increase his or her vertical jump?
A study of elite Australian volleyball players, competing on the national level, gives some guidance. The results should hold for basketball players too, no doubt, who are doing similar jumps. The researchers looked at several factors that might affect jump performance, specifically, the Spike Jump and the Counter-Movement Vertical Jump (a counter-movement vertical jump is simply a jump in which you bend the knees — the counter movement — in preparation for exploding back upwards; a spike jump has an approach, meaning some forward motion, moving toward the net).
They tested athletes for maximum single-rep strength in the squat and the power clean. They also took measurements on a force plate to measure maximum power output, which correlates pretty well to maximum strength generally (the stronger you are, the more power you can produce as a general rule). In addition, the researchers measured some basic physical characteristics of the athletes, such as height, weight and skinfold measurements (measure of bodyfat). Obviously, among elite athletes, there is less variation in bodyfat than in the general population, so they weren’t comparing obese to fit people. If they were, no doubt body fat would be the best predictor of performance.
So what was the best predictor, that is to say, the secret to jumping higher? It was the depth jump. A depth jump is a plyometric jump where the athlete jumps off a box and springs back up (in this case a .35 meter box, or roughly 14 inches). Other studies have shown that you can get the similar results with a shorter box (0.2 meters or about 8 inches).
A depth jump results in what is known as a stretch shortening cycle, meaning that on landing, the muscles stretch to absorb the impact, then rapidly shorten to respond, generating great tension and explosive force. In short, the better someone performed in the depth jump, the better that person did in the sport-specific vertical jumps.
The Australian researchers conclude that
the depth jump may be a unique overload of fast stretch-shortening cycle activity, which emphasizes a short contact time (<250 ms), fast force production, and high power outputs, all of which are considered important to jumping performance, as demonstrated by our findings and those of others. Training the neuromuscular system to generate as much tension as possible… will improve the ground reaction force in jumping.
They also say that strenght and power are interdependent and to on to say that
The results of this analysis strongly support the contention that the ability to produce high force and tolerate high tendon tension in rapid stretch shortening cycle movements is very important to jump performance in volleyball. This is best developed by depth jump training.
In other words, the depth jump builds both the strength necessary for a good jump and also activates and trians the neural pathways necessary to harness that strength.
The research team cautions that, of course, "no single strength and power characteristic is necessarily most important" and, above all, that the intense, high-impact nature of depth jumps demand that athletes progress from low volumes (in other words, start slowly and build up) in order to avoid injury.
Finally, the last "secret" is to monitor performance, measured by jump height, throughout the workout and make sure to maintain quality. Fatigue will decrease jump height and result in sub-optimal training value as well as increase the risk of injury. In plain English, quit when your jump heights start to drop off.
- Jeremey M. Sheppard et alia, "Relative Importance of Strength, Power, and Anthropometric Measures to Jump Performance of Elite Volleyball Players," Journal of Strength and Conditioning Research, 23:3 (2008), p. 758-765.