In 1980, with the Olympic trials looming, Alberto Salazar found himself with a sore knee. So, like generations of runners have been taught, he jumped into the pool . . . and got hurt. "I swam so much," he said, in the book Alberto Salazar's Guide to Running "that I gave myself tendinitis in my shoulder--so severely that I could barely manage to brush my teeth."

His isn't the only such tale. Brad Hudson, who coaches pro runners in Boulder, Colo., remembers putting an athlete on an AlterG treadmill in an attempt to get in some low-impact speed work. But the AlterG changed her stride enough that she wound up tweaking her hamstrings.

It goes to show that even the most benign-sounding forms of cross-training require a gradual buildup in volume and intensity. "You have to be prepared," says Hudson. You can't dive straight into the deep end, despite your advanced fitness from running.

Part of being prepared is understanding the risks and what to do to prevent them. Getting a sore hamstring from an AlterG might not be all that predictable, but other forms of cross-training have been around long enough that their potential dangers are well-known.

GOOD STROKE/BAD STROKE

Tom Malchow, Sydney Olympics gold medalist and former world-record swimmer, isn't surprised by stories like Salazar's. "You're asking your shoulders to do some things that are slightly unnatural," he says.

The primary risk is to the rotator cuffs, whose development can become unbalanced. The solution, Malchow says, is to supplement your swimming with strength work using rubber tubing, stretchy bands or flyweights to make sure all parts of the cuff develop evenly. (Consult a trainer for how to do these exercises safely.)

It also helps to learn proper swimming technique. "Go to a coach, or people who teach adults who are trying to take it up," he says, noting it doesn't need to be an extended class. "Even 45 minutes or an hour could [be] enough," he says.

PEDAL PAINS

When most people think of cycling injuries, they think of crashes. But cycling has its share of repetitive-stress injuries. The most effective way to avoid such issues is to have your bike properly fitted by an expert before training on it.

One common cycling injury is iliotibial band syndrome, which may be produced by cleated shoes that lock your feet into the pedal at precisely the same angle, mile after mile after mile. You can avoid this by simply dispensing with the cleats, or by adjusting them slightly. Most modern cleats allow 2 to 3 degrees of play to each side, says Kevin Dessart, director of coaching education and athlete development for USA Cycling, but referencing the need for proper bike fit, he adds,"If you're in the wrong position to start with, that isn't going to help very much."

You can also hurt your knees by putting the seat too low. Sitting normally on the saddle, you want your leg to be straight when you're at the bottom of the pedal stroke. If you have to reach for it, you're too high. If the leg is bent, you're too low. Millimeters matter.

Your position should allow you to ride with elbows bent, so that the arms serve as a shock absorber and keep road jolts from traveling up to the shoulder, neck and back. If this isn't possible, it may mean you need a different stem, shortening the "reach" from saddle to handlebars. Another important factor is the tilt of the saddle, which can throw too much weight on your hands.

Grinding out workouts in too high a gear can cause stress, particularly in the knees. Instead, spin at a higher cadence in a lower gear. The optimum cadence varies with the cyclist and the bicycle, but if you're new to cycling, you want to start by finding the gear that gives you a cadence of at least 85 RPM, Dessart says. (That means 85 full circles, or 170 pedal strokes.)

With additional training you may discover that your most efficient cadence isn't actually that high, but as you're starting out, it reduces knee stress while you strengthen your legs. "Compare it to lifting weights," Dessart says. "You're not going to recommend that somebody goes in and starts doing squats with a heavy weight load. First you do lunges, using just your body weight. It's a very similar situation, where you're not putting too much stress on your joints all at once."

Finally, be aware that cycling's limited range of motion can produce tight hip flexors. "I encourage all cyclists, and especially runners using cycling as cross-training, to stretch their hip flexors as soon as they get off the bike," says David McHenry, lead therapist and strength coach for Nike's Oregon Project.

HEALTH CLUB MACHINES

Other forms of cross-training have their risks--and tricks for minimizing them.

Rowing. The biggest concern is your back. To protect it, pull with the muscle groups in descending order of power--first the legs, then the back, then the arms, says Kelly Barten, a former youth coach and Division I rower. On the recovery, return to your starting position in reverse order--meaning you first extend the arms, then lean forward, and finally pull forward with your legs. "Legs, back, arms . . . arms, back, legs," Barten says. "The most common mistake is not remembering that rhythm."

If you're bouncing your hands over your knees, she adds, you're doing it wrong.

Also important, Barten says, is to keep your back straight by pivoting it from the hips, rather than arching it from the waist. "If you bend at the waist, you're making your back work harder than it can sustain," she says.

Elliptical trainers. These are popular, partly because they provide low-impact exercise with few risks. But not all elliptical machines are alike, and some can produce unnatural-feeling motions or force your feet into awkward positions. Also, the machine's controls need to be set at the levels that work for you. "Be attentive to your body," McHenry says. "If you start to feel soreness or tightness, you might need to make some adjustments to the resistance or cadence. If you still continue to get symptoms, you might need to find another mode of cross-training."

Exercise bikes and spin classes. Just as road bikes need to be adjusted, so do exercise bikes--a problem with some health club models where the options may be limited to giant, 1-inch increments. If you're having trouble getting it right, try switching to a recumbent, where you can fine-tune your reach to the pedal by stuffing a towel behind your back. "I think [recumbents] are better," says Matthew Matava, a professor of orthopedic surgery and physical therapy at Washington University School of Medicine, St. Louis.

The same warnings apply to spin classes. "The quickest way to hurt yourself in a spin class is to be fit improperly on your bike and then try to hammer the workout for 60 minutes," says McHenry.

Be aware, too, that some spin instructors inject exotic drills into their routines, ranging from turning up the resistance so far that your cadence drops dramatically to moving into odd saddle positions. If a drill isn't something you'd do on a road bike, don't do it in spin class either.

STRETCHING AND STRAINING

Strength and flexibility training can take many forms, but the key issues are similar for all.

In strength training, says Matava, the main concern is to work both sides of opposing muscle groups to avoid imbalance. "Supplement pull with push," he says, such as doing both leg curls and leg presses. Also, he says, don't work the same muscle group two days in a row, and avoid beginning with exercises that have you fighting for balance at the same time you're first building strength.

In stretching, yoga drew controversy last December, thanks to an article in The New York Times called "How Yoga Can Wreck Your Body." But that may be too alarmist, says David Geier, director of the sports medicine program at the Medical University of South Carolina, Charleston. "You get people complaining of strains, but it's the fanatics who are going really hard." Still, he warns, "Make sure you're doing the poses correctly."

The same can probably be said for dynamic warm-up routines. But plyometrics might be a different matter. Because these bounding exercises involve high-impact landings followed by explosive rebounds, they're a great way to tear a muscle, Matava says. "We're against it except for fit athletes under the guidance of a coach or trainer."

McHenry adds that plyometrics must be built on a good base of strength and power, not just a base of cardiovascular fitness. "Otherwise, you're ballistically loading tissue that's not ready for it," he says. "It's a really high-level thing that you have to work up to."