All data were analyzed according to the intention-to-treat principle. Differences in the primary outcome were analyzed with the use of an unadjusted chi-square test. Results are presented as absolute and relative risks and 95% confidence intervals. Kaplan–Meier curves for estimated survival were compared with the use of a log-rank test. A Cox proportional-hazards regression model was used to evaluate the influence of potential confounding factors on the outcome (factors were selected if the P value in the univariate analysis was <0.20).
Start with a ping-pong ball, then a tennis ball, then a softball, then a volleyball, then a youth-sized basketball, and on up until you can dunk with a regulation size ball. If you can't palm the ball, then you will need to learn how to control the ball with two hands until the last minute extension for the dunk with one hand, or you will have to jump high enough to dunk two-handed.
I thought I needed a rim. But what I found I really needed was a constellation of them. Having choices would prove useful because of the daytime obstacles, like elementary school PE students and our own kids’ after-school activities; and nighttime obstacles, like chain-link and padlocks, that I encountered. My training windows were narrow, so I learned to employ these outdoor rims strategically, the way the skateboarders in Dogtown and Z-Boys timed their secret sessions at drained swimming pools. The six or seven courts nearest our house featured rims that measured anywhere between 9 feet and 10' 2", a variance that allowed for different kinds of practice. The blisters and flayed calluses that soon bloodied my hands instructed me in the value of breakaway rims—the less rust the better. Because a Snap Back wasn’t always available, local residents may have spotted a sweaty forty­something man rubbing Vaseline on his hands in the corner of their child’s favorite playground last year. Sometimes he wore a weight vest that made him look like a jihadist. What I’m saying is, Thanks for not calling the cops.
To build strength in the legs that will be compatible with the speed developed through successful plyometrics drills, squat and lunge exercises are important components. Squats are performed with free weights, where the athlete uses a weighted bar to carry out the exercise. The additional weight will be supported by the body through the abdominal, lumbar (low back), and gluteal muscles, in addition to the legs. This form of exercise permits the strengthening of the legs in conjunction with enhancing the core strength of the body, essential to the balance necessary to have the several muscle groups involved in leaping work in harmony.
A forceful, dramatic move, as in That indictment was a slam dunk if ever there was one. This expression is also often put as a verb, slam-dunk, meaning "make a forceful move against someone," as in This is a great chance for us to slam-dunk the opposition. The idiom comes from basketball, where it refers to a dramatic shot in which the ball is thrust into the basket from above the rim. It was transferred to other activities from about 1980 on.

An impressive vertical jump is the ultimate standard of lower-body power and explosiveness—an attribute that pays as many dividends in high-impact sports like basketball, football, and soccer as it gets you wide-eyed looks in the gym. Increase your hops, and chances are you’ll also be able to run faster, lift more weight, and maybe even throw down a dunk at your next pickup basketball game.

A more accurate method would be to use a Jump Tester (like these here.) The problem with these, obviously, is that they are way too expensive. In fact, the only scenario in which I recommend using one of these is if you’re a coach, trainer, or athletic director who is purchasing it to test a large number of athletes over time and who needs as accurate of a number as possible for scouting purposes.
During the takeoff an athlete generates forces that ultimately result in a vertical velocity high enough to leave the ground. We have shown before, that this vertical velocity reaches 0 at the peak of the jump, and it is easy to show that the velocity is exactly the same during landing as it was during takeoff (but directed in the opposite direction).
A second, more efficient and correct method is to use an infrared laser placed at ground level. When an athlete jumps and breaks the plane of the laser with his/her hand, the height at which this occurs is measured. Devices based on United States Patent 5031903, "A vertical jump testing device comprising a plurality of vertically arranged measuring elements each pivotally mounted..." are also common. These devices are used at the highest levels of collegiate and professional performance testing. They are composed of several (roughly 70) 14-inch prongs placed 0.5 inches apart vertically. An athlete will then leap vertically (no running start or step) and make contact with the retractable prongs to mark their leaping ability. This device is used each year at the NFL scouting combine.