well no matter the case don't use air alert, it only works jupimng endurance and when i did it, it messed with my knees, but the difference is that some people are natural born jumpers (they have a very fast 1 leg takeoff) while some are power jumpers (usually a slower 2 leg takeoff) and each types needs to do either plyometrics or strength trainingif you're a natural jumper/plyometric jumper you should work on strength in the gym because that's your weak spotif you're a strength jumper you should do plyometrics to help cover that weaknessI would recommend Vertical Jump Bible (easily downloadable)it helps to classify you as what type of jumper based on muscle type, experience level and strength level