Cross-Training

Cross-training is the most natural thing in the world: You''ve been doing it all your life and probably still are. If you ran your dog on Monday, biked around the neighborhood with your kid on Wednesday and moved furniture all afternoon on Saturday, in essence, you''ve been cross-training—mixing totally different forms of exercise.

Unless you''ve participated in serious athletics, the idea that cross-training is a radical or novel concept—or even deserves to be conferred a category all its own—might seem odd. For understanding, recall the specificity principle, which declares that if you want your muscles to do a particular thing well, you must train them in just that way. Runners get better by running, lifters get better by lifting and never the twain shall meet. It''s a tiresome view of training that nevertheless inspires relentless dedication from athletes for the simple reason that it works.

Recently, however, this single track to excellence has been branching into alternate routes, inspired in part by bored athletes who found that working a little variety into their programs seemed to help rather than hinder them. One is Gordon Bakoulis, a member of the U.S. 1991 World Marathon Championship Team and author of Cross-Training: The Complete Training Guide for All Sports—an elite runner who also bikes, swims and lifts weights.

"Doing activities other than running spares me pounding, breaks up the monotony and gives me a chance to work different muscles, which helps prevent injury," Bakoulis says. "People ask how it actually helps make me a better runner, but it''s not like swimming or biking has some direct benefit. It''s more that it provides a sense of balance and just overall makes me feel better."

Physiologists who have studied cross-training say Bakoulis is on the right track. "Cross-training will never be better than specific training for a given sport, but it has many benefits for people who are interested in superior overall fitness," says Hirofumi Tanaka, Ph.D., research associate in the Department of Kinesiology at the University of Colorado at Boulder. For peak conditioning as we''ve defined it, it''s just what the doctor ordered.

The Best of Both Worlds

The underlying concern about cross-training is that by trying to do many things at once, you end up doing none of them well—that is, when performed together, one form of exercise robs another of its effectiveness.

In reality, evidence for this is mixed, which is good news: Even in instances where activities interfere with each other, the effect isn''t as significant as many coaches and trainers long believed. Although the consequences of cross-training have not been thoroughly investigated, a number of studies have been done on how various activities relate to others. Following are some of the conclusions to date.

It''s never wrong to be strong. Research on strength training consistently shows that it won''t interfere with aerobic development. "Aerobic capacity is limited primarily by the heart''s ability to pump blood to muscles," says John P. McCarthy, Ph.D., a former bodybuilder and NASA research physiologist who''s now a postdoctoral fellow at the School of Physical Therapy at Texas Women''s University in Houston. "Strength training affects muscles locally but has minimal effect in terms of oxygen uptake." And the effects that strength training does have on the heart may improve cardiovascular function. One study, for example, finds that weight training on its own can lower resting heart rate and blood pressure.

The caveat is that strength training won''t necessarily improve performance in aerobic sports. For example, weights are often used to develop the upper-body strength required for competitive swimming, but research fails to find consistent evidence that strength in the gym translates to strength in the water. One study, for example, found that when weight training was added to swim training, the weight lifters'' stroke strength improved no more than that of men who just stuck with swimming. Other studies, however, find that weight training will help cycling performance. It all depends, Dr. Tanaka says, on how closely your movements in the weight room mimic the movements of your sport.

Aerobic exercise undercuts strength—maybe. Unfortunately, aerobic exercise doesn''t appear to be as benevolent toward strength programs as strength programs are to aerobic exercise. A number of studies found that strength gains are compromised when aerobic exercise is added to weight training. It''s not that you won''t get stronger; you just won''t get as strong as you would by doing strength training alone. "The impairment isn''t great, but it is statistically significant," reports Dr. Tanaka.

These findings may be skewed, however, according to Dr. McCarthy. He points out that studies often require cross-training subjects to do two programs at full tilt simultaneously: The cross-trainers are exercising more than the people to whom they''re being compared and, it''s safe to assume, are more tired. "Exercising up to six days a week, as some of these studies require," he says, "is just not realistic." When Dr. McCarthy conducted a study of sedentary men in which exercisers—whether they were only lifting weights, only doing aerobic exercise or combining the two—all stuck to a three-day-a-week program, he found no difference in strength gains between the weight trainers and the cross-trainers.

All aerobic exercises are not equal. You might assume that one form of aerobic exercise will improve cardiovascular endurance as well as another, but some activities appear more complementary than others. How well a combination of activities works depends in part on how fit you are before starting: Studies find that less-trained men or average exercisers interested in fitness show greater improvements from cross-training than do men who are already highly trained.

Beyond that, to get the most out of multiple activities, it makes sense to combine forms of exercise that use the same muscle groups. For example, running and cycling seem to complement each other well: Runners who take cycling tests and cyclists who take running tests all show substantial increases in oxygen uptake after training. (Caveat: Cycling helps runners more than running helps cyclists.) Dissimilar activities like running and swimming, however, "may have little practical benefit" if you''re highly trained, concludes one research review.

Cross-training burns more fat. Aerobic exercise gets all the glory for fat-burning and weight loss, but strength training has tangible benefits of its own. Not only does strength training raise the body''s fat-burning metabolism during the workout but adding muscle—which requires more fuel to maintain than fat does—keeps the metabolism firing at a higher rate even when you''re resting. Together, strength and aerobic training are dramatically superior at burning fat than either one alone.

In one study of men and women who ate the same diet, for example, those who split their half-hour workouts into equal parts strength training and aerobic conditioning lost twice as much body weight as those who did only aerobic exercise.