Q.I have begun using a mini-trampoline to jog because I get shin splints when I jog outside on the roadways. Are there fewer physical benefits to using a trampoline than with regular jogging? How much time spent jogging on the trampoline is necessary to approximate one mile of regular jogging? Am I wasting my time?

G.F.

Herndon.

A. The mini-trampoline is one of the newer jogging devices. It's a small trampoline with a bed just large enough to allow a person to jog in place.

First of all, you are not wasting your time. Any exercise is better than none.

You've indicated that shin splints have been a chronic problem. If you really enjoy jogging (and you've tried all the shin splint remedies) the mini-trampoline may be your only jogging option. It will minimize the pounding forces of normal jogging.

The mini-tramp, however, offers fewer physical benefits than normal jogging because the muscles are required to do less work. The recoil of the resilient tramp bed throws the foot and leg upward, meaning those muscles don't have to push and pull as hard as they do during normal running. In fact, Dr. Ken Cooper, in his book "The Aerobics Program for Total Well-Being," points out that several studies have shown that you use less energy running on a trampoline than you do running in place.

In addition, the range of motion of the hips and legs is extremely limited on a trampoline. While you're jogging or running on a flat course, the muscles are exercising through a greater range as you extend the legs forward and backward. That greater work provides greater muscular and aerobic benefits.

You asked for a formula for mini-tramp use that would approximate the exercise of a mile jog. Remember, it's paramount that you be concerned with time and intensity, not distance. Monitor your heart rate. If you're healthy, exercise at a rate that keeps your heart rate between 70 and 85 percent of its recommended maximum. Continue the exercise for a minimum of 12 minutes and preferably 20.

With that in mind, here's an example from Dr. Cooper on gauging the aerobic benefits of running on the mini-tramp: Exercise at a rate of 60 steps per minute, counting only when the left foot strikes the surface. The feet should be raised at least eight inches each step. Exercise for 10 minutes. This rate would have the same aerobic benefits as running a mile in about 121/2 minutes.

A 121/2-minute mile means an average speed of 4.8 miles per hour. How fast is that? Five mph is generally considered the break point between walking fast and jogging. In other words, you could walk fast (just short of a jog) and complete a mile in 121/2 minutes. Unless you were in extremely poor cardiovascular condition, you wouldn't improve at that rate.

There are advantages and disadvantages to every mode of exercise and type of equipment. People with joint or muscular problems may find that the mini-tramp is a useful alternative to jogging. You might also try swimming or riding a stationary bike as an alternative. If you do use the mini-tramp, make sure you monitor your heart rate to ensure adequate workload to stimulate an increase in your cardiovascular condition.

If the mini-tramp is your only form of exercise, I'd recommend that you find some way to progressively overload the muscles, especially if you're middle-aged or older. In my opinion, additional stress will be required to prevent the muscle and bone losses that result normally from aging.

I encourage any form of exercise if it's not dangerous. Some forms are better than others. If you're asking if there are better forms of exercise than running on a mini- trampoline, my answer is yes. Would these other forms be better for you? Maybe, and maybe not.

If you have regular access (three to four times a week) to the mini-tramp and it doesn't aggravate your shin splints, then I'd recommend you bounce your way to a better level of fitness.