Q. How do you improve jumping or leaping ability, or is it just natural ability? How much improvement can I expect? What exercises would you recommend? D.H.

Oakton, Virginia A. Jumping is a skill, and to improve any skill you have to refine the neuromuscular pattern involved. Fortunately for you, jumping is a gross motor skill -- it doesn't require much practice before you refine it. How much you improve overall, however, is determined by your willingness to work and your genetic potential.

Here are some of the factors involved:

* Maturation. Leaping ability generally grows as bones and muscles grow stronger. But by age 23 most people have reached the limits of gains attributable to maturation.

* "Recruiting" muscle fibers. We all have some dormant muscle fibers that aren't hooked up to the brain, so they can't be recruited. It's like having an 8-cylinder engine with only six spark plugs connected to the distributor. You can have what appears to be a big engine but lack the expected power because two of the cylinders aren't working. The ability to recruit muscle fibers is an inherited trait. If you're lucky, your parents provided you with the best connections.

* Quality of muscle fibers. For ease of explanation, let's say that there are two different types of muscle fibers. One is for fast, explosive, short-term use. The other is for sustained use over a longer period of time; these fibers provide better endurance.

Oversimplified, these are called fast-twitch and slow-twitch fibers. The more fast-twitch fibers you have, the better potential you have for jumping. Everyone has both types of fibers. But the great sprinters and leapers have a much higher percentage of fast-twitch fibers.

You're probably wondering if you can increase the number of these fast-twitch fibers. At present the research community tells us no. The number of fast-twitch fibers you possess was determined at conception.

* Sequence of recruiting muscle fibers. No matter how much they practice, some people can't effectively perform a skill -- throwing a dart, jumping -- because of their inability to recruit the right muscle fibers in the right sequence. It's like having the timing off in your car. You step on the accelerator but it doesn't respond smoothly. So, once again, your level of skill depends on the genes your parents gave you.

Having practiced jumping -- the best way to do that is by playing basketball -- and taken all those factors into consideration, the only other means you have to improve your vertical jump is to strengthen the muscles used to jump. The buttocks are the major muscle group used to leap. The other major muscle groups of the legs also assist, including those muscles that cross the hip and knee joint (hamstrings, quadriceps hip flexors, adductors, abductors, calves).

Strengthening the leg and buttocks muscles is something you have control over. How much will your vertical jump improve with an increase in leg strength? I don't know. Nor will you until you strengthen them and find out.

The exercises you perform will be dictated by the equipment you have available. Standard exercises include the squat, leg press, leg extension, leg curl and calf raise. Any exercise you can do to isolate the buttocks is highly recommended.

Practice vertical jumping until you've refined the skill, make allowances for maturation, strengthen the muscles used to vertical jump and hope that you've inherited a finely tuned machine from your parents. Do all of this and then follow the advice of the Pointer Sisters -- "Jump, Jump, Jump."