Jumping higher is always a popular goal for a lot of people in the weight room. People go about it by different ways -- plyometrics, leg press, jumping programs like "Air Alert" -- but at the end of the day one of the best ways to increase your vertical leaping ability is with the squat. A back squat (or front squat, or split squat) is about as functional as it gets when it comes to mimicking the pattern of a jump.
It's not just about throwing some weight on your back and sitting down and standing up, though. Squat depth, as always, plays an important role. A 2012 study by Hartman et al in the Journal of Strength and Conditioning Research studied the relationship between squatting depth and changes in vertical jumping performance. Putting the subjects through a 10-week periodized maximal strength training program, they created and tested four groups: a control group that was not allowed to perform any strength training, a group that performed deep front squats, a group that performed deep back squats, and a group that performed quarter back squats. Deep squats were defined as "going below parallel." Quarter back squats were defined as possessing 120 degrees of knee extension, and were performed in a Smith machine.
The results were certainly interesting and very telling. Two types of vertical jumps were tested: the countermovement jump (from a standing position, you quickly squat down -- the countermovement -- and then explode up) and the squat jump -- from a squatting position, you explode upwards. The control group, on average, so no increase in countermovement jump (herein referred to as CMJ) ability, and less than a 2% increase in squat jump (herein referred to as SJ) ability. The quarter back squat group saw a slight DECREASE in CMJ ability, with a 2.68% increase in SJ ability. The deep front squat group saw an 8.29% and 7.19% increase in CMJ and SJ ability, respectively. The deep back squat group saw a 7.79% and 5.83% increase in CMJ and SJ ability, respectively.
The study showed that maximal strength training via front and back squats that utilize proper depth have a significant effect on affecting one's jumping ability. The study was not without its limitations, though. Maximal strength was trained for, with the issue being that the jump is more dynamic and not entirely conducive to maximal strength training. The subjects worked on hypertrophy for the first 8 weeks of the study, with the final 2 weeks seeing a strength-power period of 2-4 repetitions. More power training would like have seen an increase in vertical leap ability. As well, utilizing the "dynamic effort" method could have seen more gains. In short, the dynamic effort method utilizes submaximal weights being moved at maximal speeds. In layman's terms, that means lifting much less than your max as fast as you can. Example: your 1RM (one rep maximum) for squat is 315; you may use 185 or 225 and lift that 6-10 times as fast as you possibly can. This trains the body in an explosive fashion, much like a vertical jump is explosive.
Conclusion: squat depth influences jump height. If you want the inches on your vertical, get below parallel.