A coaching colleague of mine has a basic formula for cross-training: 60 minutes at or above 70 percent of your maximum heart rate equals a five-mile run. He uses this formula with his athletes in the summer to allow them to augment their base miles. He also uses it during the cross-country and track season when a runner becomes injured, and during the winter when inclement conditions make it difficult to keep actual running mileage high.
Is a cross-training mile exactly the same physiologically as a running mile? Nope. But intense cross-training for an hour can elicit the same aerobic benefits as a five-mile training run. And because of the low-impact nature of most cross-training activities, injury-prone runners can beef up their "mileage" using this formula without increasing their risk of injury. In the following two case studies, both Lisa and Dave used cross-training miles to become better runners.
Cross-training Through Injury
Lisa, a good college cross-country runner, had been injured in a car accident. When her injury had mostly healed, she was able to run but could maintain only about half of her preaccident mileage. Working out on either an elliptical trainer or a stationary bike for an hour a day, Lisa increased her cross-training mileage quickly. More importantly, the supplemental workouts enhanced her aerobic fitness, which allowed her to increase her actual running mileage. And even though her total mileage skyrocketed to 115 per week (50 cross-training miles plus 65 running miles), Lisa's morning resting heart rate remained the same, which indicated she was not overtraining. By the end of the summer, Lisa had the strength and energy to lead her college to a top 10 NCAA performance in cross-country and garnered all-American honors.
Cross-training to Lose Weight and Boost Fitness
After four years of competing for his college cross-country team, Dave took a two-year break from running to live and work in Spain. When he returned from Europe 30 pounds heavier, he tried to run again and found that the extra weight made his knees and hips hurt. That joint pain, coupled with his lack of aerobic fitness, made it difficult for Dave to run long enough to lose the weight. Over a three-week period, Dave gradually added up to an hour of cross-training per day (elliptical, stationary bike, and pool running) to his 30- to 45-minute daily runs. As his weight dropped and his fitness increased, Dave could run farther and faster with no pain. After several 50-mile weeks (25 cross-training miles plus 25 running miles), Dave dropped the extra weight, then continued to cross-train twice a week for enjoyment and additional weight maintenance.
Four Keys to Cross-Training for Runners
1. Choose workouts that are closest to running in terms of muscles used and aerobic systems taxed. Good options include elliptical trainers, cross-country ski machines, stationary bikes, and water running.
2. When cross-training, keep your heart rate at or above 70 percent of your maximum heart rate (220 minus your age) most of the time. In other words, you should be working hard and sweating a lot.
3. Check your morning heart rate regularly. An elevated morning heart rate is a sign of overtraining, which can occur if you add too much cross-training too soon.
4. Combine cross-training with running to maximize running fitness with lower actual mileage. You can substitute 25 to 30 percent of your weekly "mileage" with cross-training.