HOW MUCH WILL I GAIN?
This is probably the question I've been asked more than any other since I began helping people train. Everyone wants to know, "How many inches in a month?" "Can I dunk before this date?" "Do you think I can reach 50 inches?" And so on. Unfortunately, the first thing I have to tell people is simply, "I don't know." There are too many factors involved, and I can only attempt to control one. All I can do is provide a solid training plan and effective instructions for the exercises. I can't make anyone follow the program, use correct exercise techniques, stretch properly, take the necessary time off, get good nutrition, etc... An example. A friend of mine was using training from my website for a couple months. He had seen very little improvement and ended up not training for awhile. He recently asked if I would train him personally. I was fully willing. He told me his max squat was around 225. His first workout with me, he squatted 245 five times with no trouble. He had no idea how strong he was and had been lifting far less than he should have. I have no way to ensure that people who use my site won't make a crucial mistake like that. And even if someone does train correctly, I still can't promise gains, because unfortunately we do not have push-button control of our bodies. When you put a stimulus on your body, there is no guarantee it will respond well. It's not uncommon for people to lift weights for months without ever getting any stronger. (That's actually the primary frustration of many athletes.) There are things you can do to help your body, namely intelligent training, getting rest, and proper nutrition. But nothing is guaranteed. Pardon this discouraging paragraph. It's important to make that clear.
Most people who train properly will have success in improving their vertical jump and all around athleticism. Unfortunately the marketing promises of some of the jump training programs on the internet have severely distorted people's idea of what successful training is. 20 inches guaranteed? 10 inches in 6 weeks? Double your vertical leap? To promise these results is ludicrous. I hope to give you some more realistic expectations.
There are a couple general trends to understand. First, the younger you are, the easier it will be to make gains. (note: I don't recommend training for kids who have not reached puberty. Just playing sports will provoke strong athletic development in children.) When your body is still growing and developing, it will respond very well to just about any stress, particularly if you are on a growth spurt. (see the About Me page) As you get older, recovering from training will become a much longer and more difficult process, especially once you are done growing. Personally, my strength gains were practically immediate when I was 13, still consistent when I was 17, and quite slow by the time I was 19. Individual patterns will vary; just know that age slows things down. Secondly, the better an athlete and the more highly trained the athlete, the slower the gains will be. Going from a 20-inch to a 30-inch vertical is far easier than going from 30 to 40. Consider a world-class high jumper. He'll train for 4 years between Olympics in hopes to clear 3-4 inches higher. Gains slow down as you reach higher levels of athleticism.
With these things in mind, let's look at some examples. A young, untrained beginner athlete may gain an inch on his vertical every week at the beginning of his training. This is a fantastic experience, but it won't last. Let's say he starts with an 18-inch vertical. If his initial rate of improvement continued he would have a 70-inch vertical in a year. No one has ever had a 70-inch vertical. This athlete may gain 8 inches in two months and then train for 6 months to get the next 3 inches. A similar scenario could happen with a beginner athlete in his early 20s, but the gains will most likely be on a smaller scale. He may gain 5 inches in 2 months. But again, if that continued he would add 30 inches in a year. That does not happen. Gains always slow down. Another scenario. A young athlete may make significant strength and power gains but a lack of coordination or a lack of flexibility could hold him back. He will likely see improvement in some athletic movements, but peak measures like the vertical jump or top speed sprinting may remain stagnant. Months down the road when this athlete develops coordination to jump properly or starts stretching consistently, the gains from the past months will suddenly begin to show, and his vertical could shoot up very quickly. This is an example of why it is important to evaluate weak areas and work on improving them as soon as possible.
Several different factors explain why training progress slows down so much. First, a higher level of athletic performance requires a stronger training stimulus to provoke more advanced adaptation in the body. This adaptation is more difficult and takes a longer time. Example. When someone first begins strength training, the biggest factor in their strength increase is the activation of additional muscle fibers. This is an easy adaptation, and a beginner lifter will have a large percentage of previously inactive fibers to recruit. So initial strength gains are large. As the percentage of fibers used gets higher, there are less new ones available to be activated, so that method of adaptation decreases. An example with plyometrics. Adapting to line hops, a beginner exercise, is far easier and takes less time than adapting to depth jumps, an advanced exercise. Second, the body's adaptability decreases over time. This happens partly because a stimulus provokes a greater response when it is new. The body is not as shocked the second, third, fourth... time around. The body also seems to run short of "adaptation energy". This is not yet a well explained phenomenon; it's just what always happens. Restoring the body's willingness and ability to adapt is the main reason for taking time off from training. Third, the stimuli and adaptations of different types of training conflict with each other more and more as they reach higher levels. Strength training provokes a stiffening of the muscles and tendons, basically making them more like steel cables. Plyometrics aim to make them more like rubber bands. Also, the neural impulses of strength training may be strong, but they are not necessarily fast, so the stimulus on the nervous system is different than plyometrics or explosive lifting. This is why elite powerlifters are not especially explosive and certainly not springy athletes. In a beginner athlete, the springiness needed to jump 26 inches is hardly going to be affected by squatting 1.2 times bodyweight. But the stimulus of squatting 1.8 times bodyweight and doing depth jumps off a a 24-inch box are very much in conflict. So while improving one area, an advanced athlete will often have to sacrifice some ability in the other. Obviously progress will be much slower than for a beginner athlete who can improve in all areas simultaneously.

With these things in mind, once past the growth spurts of youth and the strong adaptations to the first months of training, a sort of step-by-step approach must be taken to sports training. The basic idea is to first develop strength, then develop the ability to utilize that strength for athletic movements. Let's say an athlete is pretty evenly developed in strength, explosiveness, and plyometric ability. The first step is to increase strength, which creates potential for athletic improvement. Because plyometric ability may suffer from strength training, the increase in strength may not produce immediate athletic gains. Improvement in one area is balanced by decline in another. The next stage of training will hopefully allow for further strength increase, but it will be done with higher intensity and less volume, allowing for more training of explosiveness and plyometric ability. One might expect to see athletic gains during this time, but it is often the case that intense neural training such as plyometrics and Olympic lifts take a long time to adapt to, so again gains may be minimal. The third step is to completely eliminate strength training and allow for full development of the springlike quality of muscles and tendons. The term I use for this is a peaking phase. This is likely when athletic gains show up, but they also may not come until a time of rest. That is a testament to the time that may be required for neural recovery. One thing to note is that plyometric ability is quite limited. It is possible to be as springy as you're ever going to be. Once you get to that point, further plyometric training will do no good. The goal then has to be to go back and gain more strength and explosiveness. Then regaining that peak plyometric ability will result in higher performance because of the other improvements. Strength and explosiveness also have limits obviously, but they are far beyond the reach of all but a select few. Generally speaking, it is always possible to get stronger and more explosive. Unfortunately, this process of advanced athletic development is slow and fragile. Injury or sickness can easily throw the entire process off, resulting in wasted months or even years of training.

Given the details of this process, there are some things to keep in mind. Noticeable athletic gains are not likely to show up consistently throughout training. It's far more likely to see chunks of improvement during times of recovery. So when vertical training, don't count on two inches each month. In fact, some training phases will temporarily decrease your vertical. Instead focus on making training improvements. If you reach your desired flexibility level, that's success. If you get stronger, that's success. If you bounce up quicker on depth jumps, that's success. It's only at certain points in training that all those things will blend together to create a higher peak vertical jump. Thinking back to the variety of different recovery abilities that people have, patterns of athletic improvement will vary. One of the best things you can do for yourself is get to know your body. Learn how your body responds to different training. For example, my friend Chris and I have his pattern figured out pretty well. The past three semesters of school, he has lost a few inches on his vertical at the beginning of training, experienced small fluctuations for the next few months, and then seen his vert shoot up to 3 or 4 inches higher than ever when he takes time off. Chris has had no trouble making improvements when focusing on strength, but it takes a long time for his explosiveness and springiness to kick in. On the other hand, I struggle to make strength improvements, but tend to adapt fairly quickly to plyometrics. I've even had a few next-day vertical improvements from that type of training. Understanding your body will help you make intelligent training decisions.
In the end, the pursuit of great athletic ability is long and hard. One must be able to persevere through failures, trial and error, setbacks, and so on. Fortunately, the reward is great.