The question has occurred to many endurance athletes, and it seems so basic: Will cross-training — doing a second sport, or lifting weights on days when you aren’t running or cycling or swimming — improve your performance in your primary sport?
And at first glance, the answer might seem to be an obvious no. If you want to be a better runner, you have to run — regularly, consistently, and with a training plan that forces you to gradually increase your distance and speed. If you want to be a better cyclist, you have to ride and train according to the same principles. Same goes for swimming or any other endurance sport.
But there also is a body of opinion that says cross-training is necessary and important if you want to improve your performance and avoid injury.
The science, though, is not nearly so definitive. And the answer as to what, if anything, cross-training can accomplish depends on your goal.
The American Orthopedic Society for Sports Medicine encourages cross-training, saying that it can provide a “ ‘total body tune-up,’ something you won’t get if you concentrate on just one type of activity,” and that “you may experience fewer overuse injuries.”
But the purpose of its recommendations is overall health, not performance. If that is your goal, researchers say, it is not so clear that cross-training in an alternate sport will help.
Hirofumi Tanaka, an exercise physiologist at the University of Texas in Austin, came to that conclusion more than a decade ago in a review of published papers. Studies comparing athletes, both trained and untrained, had found that only one factor mattered if performance was the goal: training in that sport.
The results make sense, Dr. Tanaka said. Each sport uses highly specific muscles and nerves. Using an elliptical cross-trainer may feel as if it is exercising your running muscles, but it is not giving you the same kind of training that running does. Nor does it train the muscles you need for cycling.
“You can maintain your cardiovascular capacity by cross-training, but it is extremely difficult to maintain your performance when you rely on cross-training,” Dr. Tanaka said. “This is because you are violating the principle of the specificity of training.”
Anyone who has been injured and forced to do an alternate sport knows this already. If you cannot run and end up substituting workouts on a bicycle for running, almost invariably you will end up losing running speed and endurance.
But if an alternate sport doesn’t help endurance athletes, resistance training might. It’s a bit counterintuitive — if you are training for an endurance sport like running, your workouts increase your ability to perform the same motion over and over again but do not markedly increase your muscle strength.
Lifting weights is just the opposite — you do a few repetitions with the goal of increasing muscle strength and size. Yet in a review of published studies, Dr. Tanaka found that resistance training improved endurance in running and cycling. The effect occurred both in experienced athletes and in novices.
A more recent study of experienced runners by a group of Norwegian researchers confirmed that weight lifting could increase performance. One group did half squats with heavy weights three times a week while continuing a running program. The other group just ran. Those who did the squats improved their running efficiency and improved the length of time they could run before exhaustion set in.
Similar studies also have found the effect in cyclists, but not in swimmers, Dr. Tanaka said. Swimmers do get faster, however, when they try a very specific type of resistance training, done while in the water, that concentrates on the movements they use in their strokes.
It is not known why weight lifting would improve performance, but investigators speculate that it may train supporting muscle fibers in the legs, allowing runners or cyclists to use them to augment muscles that get tired.