For smaller guys much of the problem, and one I struggled with, is managing the ball. Like most guys my size I can palm a basketball if a grab it carefully, but realistically it isn’t going to happen without a little concentrated effort. Some of those big guys can make a basketball look like a volleyball, and they have no trouble getting hold of it and shoving it over the rim.
Start on a lower hoop and practice on that, just to get the feel of dunking. Jump height is one thing, but you would be surprised at the number of people that find it hard just to slam the ball into the basket, even if they are high enough. Make sure the hoop is high enough for you to only touch the rim. Different jumping styles and distances from the basket can change your vertical drastically and could be the difference between a rim-block and a slam. Keep progressing and eventually you will see results. Good luck!
Unfortunately, I’m not the 6' 7" son of a Hall of Famer, so I had to resort to desperate devices—like Hennessy, an infamous and inexpensive cognac that, according to one of the two NBA players who recommended it to me, “will give you that Yah! That bounce. That little bit of meanness you need.” The little minibar-sized bottle that I downed 30 minutes into an intense session of dunk attempts on a sweltering day last summer, had no effect other than scorching my esophagus, giving me a headache and releasing from my pores an aura that, as my six-year-old put it that evening, “smells like medicine.”
“There’s something about dunking a basketball that lures us in,” he said, reflecting on his first jam, during lunch period his sophomore year at De La Salle High in Concord, Calif., back when his driver’s license read 5' 11", 112 pounds. “It stokes the imagination. It’s something you always dream of doing. I have a friend whose father, at age 50, is trying to dunk.”
When performing a vertical jump, the athlete exerts force at the low back, hip, knee, and ankle joints. The spine flexes as the athlete squats downwards, and then is extended by the spinal erectors over the course of the jump. The hip extensors (gluteus maximus, hamstrings, and adductor magnus) work to move the trunk and the thigh apart, which pushes the torso up and backwards. Meanwhile, the knee extensors (quadriceps) contract to extend the knee, and the calf muscles contract to move the shin backwards, towards the vertical.
variations: The vertical jump test can also be performed using a specialized apparatus called the Vertec. The procedure when using the Vertec is very similar to as described above. Jump height can also be measured using a jump mat which measures the displacement of the hips. To be accurate, you must ensure the feet land back on the mat with legs nearly fully extended. Vertical jump height can also be measured using a timing mat. The vertical jump test is usually performed with a counter movement, where there is bending of the knees immediately prior to the jump. The test can also be performed as a squat jump, starting from the position of knees being bent. Other test variations are to perform the test with no arm movement (one hand on hip, the other raised above the head) to isolate the leg muscles and reduce the effect of variations in coordination of the arm movements. The test can also be performed off one leg, with a step into the jump, or with a run-up off two feet or one foot, depending on the relevance to the sport involved. For more details see vertical jump technique.
The phrase "slam dunk" has entered popular usage in American English outside of its basketball meaning, to refer to a "sure thing": an action with a guaranteed outcome, or a similarly impressive achievement. This is related to the high probability of success for a slam dunk versus other types of shots. Additionally, to "be dunked on" is sometimes popularly used to indicate that a person has been easily embarrassed by another, in reference to the embarrassment associated with unsuccessfully trying to prevent an opponent from making a dunk. This ascension to popular usage is reminiscent of, for example, the way that the baseball-inspired phrases "step up to the plate" and "he hit it out of the park," or American football-inspired phrases such as "victory formation" or "hail Mary" have entered popular North American vernacular.

I'm 33 yrs old, turning 34 in a month. I stand 5'7" and weigh 155 lbs. I used to touch the rim with both hands but now I can only touch the back board... I almost came close to dunking, but that was when I was 22 years old. I still dream of dunking one in...but I think the exercises that I used to do...don't seem to work anymore... Is it still possible for me to dunk even at this age?

Want to increase your vertical jump for volleyball fast? The easy way is to use our vertical jump bands and wear them while you practice your spikes! Just put on the vertical jump bands during volleyball practice and you'll be training your vertical jump while you are also practicing your volleyball skills. This means you don't have to do extra vertical jump workouts to gain inches on your jumping ability.

Vertical jump measurements are used primarily in athletic circles to measure performance. The most common sports in which one's vertical jump is measured are track and field, netball, basketball, football, and volleyball, but many sports measure their players' vertical jumping ability during physical examinations. In addition, single and multiple vertical jumps are occasionally used to assess muscular strength and anaerobic power in athletes.[3]