Adam Fleischer’s CD4 cells have jumped from zero to 300-and-holding during the past two years; his viral load is now undetectable. His weight has climbed back up from a gaunt 118 pounds to a steady 135. He’s had no new opportunistic infections and his KS has not recurred. Fleischer, a New York City marketing executive, is quick to credit his seven-year survival with AIDS to state-of-the-art medical care, including the latest drugs, top-flight nutrition, acupuncture and massage.

But he’s not referring to his current pharmaceutical regime (Crixivan/AZT/3TC) when he says, “It’s one of the biggest reasons I’m alive today.” He’s talking about the three hours per week of moderate exercise he began at his doctor’s urging just before his blood work began turning around. “I’m absolutely convinced that working out has played a huge role in my T-cell increase and sustained health improvements.”

He’s not alone in his belief.

“I’ve always known that exercise promotes immunity,” says Joe League, a world-class marathoner and much sought-after training partner by many of this country’s most elite endurance athletes. "Back in the ’80s when the epidemic first began, I made my living as a stagehand for the Ice Capades. Many of the skaters and coaches were gay, and at first it seemed to me that the older guys were dying fastest. Then I realized that the guys who were still in training were just lasting longer."

For the past 10 years, League has groomed a San Diego team of recreational runners with HIV, most of them nonathletes to begin with. Their proud coach boasts, “I’m HIV negative and out with more sick days than they are.”

There’s hard science that may explain why his HIV positive teammates feel so good, while League seems to catch every bug that comes along. “We know that natural killer cells operate at higher levels in fit people, and that moderate exercise increases the number of immune cells in circulation without raising stress-hormone levels,” says David Nieman, an elite distance-runner himself and one of the handful of laboratory physiologists who looks specifically at the effects of exercise on immunity. “Increase the intensity of exercise too much,” warns Nieman, “and there’s definitely a point of diminishing returns.” Coach League may be getting sick more often because his own workouts are much harder and longer than those of his weekend warriors.

“The danger lies in overtraining, not undertraining,” says Fleischer’s coach, Bill Vayo. As a program director at Plus One, a medically based fitness clinic in New York City, Vayo has trained people with HIV on both ends of the fitness scale: The hardcore jocks who’ve never been sick as well as the more fragile folks recovering from opportunistic infections. The former marine recommends that novices and seasoned athletes alike err on the side of comfort: “Without instruction or supervision, most people naturally exercise at a beneficial intensity. Problems arise only when we push too hard and get run down or injured.”

The trick is finding that highly individual balance of just the right combination of exercises at just the right intensity. “We all have different starting points and different rates of progression,” says Vayo. “When Adam first came to Plus One, he was wasted and out of shape. His chart had 15 pages on medications alone.” Standard calculations of body composition, maximum heart rate and lung capacity were useless for designing his fitness program.

Vayo and Fleischer solved this complex physiological problem by employing a simple method for “rating perceived exertion” or RPE (see chart). They chose a target range on a one-to-ten scale, and stuck to it throughout each training session. Fleischer gradually increased the intensity of physical activity until he could sustain two or three hours per week between a “very light” and “somewhat hard” workout -- thus realizing all the benefits of exercise without losing weight or making himself sick.

Instead of dogging himself to bench press some set number of reps at some arbitrary weight, or huffing and puffing to cover some predetermined distance on the treadmill, Fleischer keeps his RPE fairly constant each day through each exercise. If he’s tired or sluggish, he lands in his target range sooner. If he hits the floor raring to go, it is longer coming. The workouts adjust themselves automatically without any fancy calculations or head trips.

Fleischer’s basic workout is no different than that of a competitive athlete. It only varies in intensity. All sensible cross-training programs incorporate a mix of progressive-resistance exercise (such as weight-lifting) with aerobic work (such as walking, jogging, biking or swimming) to address the five basic components of fitness: Body composition, flexibility, muscle strength, muscle endurance and cardiovascular endurance.

Basic body composition is chiefly a function of genetics, but we can certainly increase our lean muscle mass and minimize wasting -- even in the face of underlying disease -- through diet and exercise. Flexibility has no direct impact on immunity, but if we can’t bend and turn and push and pull things comfortably, we end up with injuries that interrupt training and we’re back to square one.

We can make muscles bigger and stronger by regularly loading them with progressively more weight over time. For upper-body work, that means anything from pressing and curling soup cans in bed to weight-lifting, push-ups and pull-ups in the gym. For the lower body, it can range from simple exercises with attached ankle weights (as light as you need them to be) to squats and lunges. Just climbing the stairs at the office and at home can contribute. Muscle endurance is improved by repeating a motion over and over.

Most important of all, you can improve both cardiovascular fitness and immunity by conditioning the heart and lungs with aerobic exercises. Don’t forget that it’s your cardiovascular health that will determine how quickly you recover from physical stress.

Researchers agree that most of us need at least 20 minutes of aerobic activity two or three times a week to see any long-term improvement. A training plan will deliver only minimum gains unless you regularly pump up your heart rate long enough to sustain a light sweat, while still being able to talk without gasping for breath. If you keep your eye on the RPE chart, you’ll do enough without doing too much. And never forget that exercise must always be accompanied by good nutrition and plenty of fluids. (See "Go With Your Gut“ and ”Water Sports.")

So if exercise is so bloody good for us, then how come 80 percent of Americans are still glued to the couch? Part of it is money. No insurance company is about to reimburse us for joining a gym or hiring a trainer to help develop a personal fitness plan. But most physicians will refer you to a physical therapist who can help formulate a well-rounded strategy. Part of it is time -- how to fit regular exercise routines into a busy life. But finding the time doesn’t have to be all that difficult. As Vayo recommends, “Don’t make workouts a time-consuming chore. Get off the train one stop early, walk to work, take the stairs.”

For many, the greatest barriers are social and often self-imposed. Either we’re too self-conscious to cut through the attitude in a room full of ripped gods, or we were brutalized by the jock culture when we were kids. Besides our adolescent traumas, we’re tormented by the body-beautiful consumer culture long after we’re grown, inundated with images of buff physiques most of us will never remotely approximate. Women and gay men especially understand the demoralizing stress of relentlessly being sized up by your tits and ass. No wonder most folks would sooner eat glass than set foot in a gym.

But before you let any of these barriers stop you from exercising, you may want to listen to Adam Fleischer, who summarizes the potential benefits from exercise very simply. He says, “There’s powerful medicine out there in the wide world of sports.”