As I rode the exercise bike in the lab this morning, it occurred to me that there are 3 good reasons to cross train: 1) you are injured and canít run, so you need to do something to keep your sanity; 2) you want to improve your cardiovascular fitness without getting injured; or 3) you want to improve your running by doing other activities (such as weight lifting or yoga) that do not target your cardiovascular system.
The first 2 reasons to cross train involve maintaining or improving your cardiovascular fitness. Cycling, rowing, in-line skating, swimming, stair climbing, and deep water running fall in this category. The third reason covers all of the other activities you can do to enhance your running performance. Weight lifting, yoga, and stability ball sessions fall into this category. In this monthís column we will focus on cross-training to improve aerobic fitness, and next month we will look at other forms of cross training.
Studies have shown that predictable training errors such as increasing mileage or adding speedwork too quickly lead to the majority of running injuries. Just as the risk of coronary artery disease can be reduced through regular exercise, so can the risk of running injuries be reduced through modifying risk factors. One way to do this is to reduce pounding on the legs and back by substituting other forms of exercise for a portion of your running.
But, wonít your racing performances suffer if you replace some of your running with cross training? The Principle of Specificity of Training says that your body adapts very specifically to the type of training that you do. That is why you wouldnít have much success as a runner by doing all your training on the bike or in the pool. But, what if the majority of your training is running, can you enhance your cardiovascular fitness by doing other types of aerobic workouts? Letís see what the research says.
In a 1995 study published in the European Journal of Applied Physiology, Carl Foster, Ph.D. and colleagues investigated the effects of increasing training volume via additional running versus as equal increment of cross training. Thirty reasonably well-trained runners were divided into 2 groups. One group (run + run) increased their running mileage by 10% while the other group (run + swim) added an equivalent amount of swimming to their training. After 8 weeks of increased training, the run + swim group improved their 2 mile race performance by 13 seconds whereas the run + run group improved their 2 mile time by 26 seconds. In addition, the 4 mmol lactate threshold improved in the run + run group but not in the run + swim group. The results of this study suggest that even reasonably well-trained runners can improve their running performance through cross-training, but that the improvement is likely to be less than through increased running.
A 1995 study published in the International Journal of sports Medicine investigated what would happen when runners double their training volume for 10 days by either: 1) doubling their running mileage (run + run) (do not try this at home), or, 2) adding an equal amount of cycling (run + cycle). Eleven well-trained male runners participated in this study. The subjects performed a 5K time trial the day before and the day after the increased training. Surprisingly, the runnersí times did not change appreciably after the 10 days of (run + run) or (run + cycle) training. Wouldnít you have thought that after 10 days they would be really tired? This study would have told us more about cross training and performance if the runners increased their training for several weeks rather than 10 days and then had a few days to taper before the second 5K time trial.
A 1993 study published in Medicine and Science in Sports and Exercise investigated the effects of 5 weeks of increased training intensity through running and cycling versus running only in moderately-trained runners. Both groups increased their VO2 max values from 55 to 58 ml/kg/min, and improved their 5K times by over a minute and a half. These results indicate that similar improvements in running performance can be attained by either increasing running training or the addition of cross training in moderately trained runners.
One of the best studies on cross-training and runners was published in the February 1998 issue of Medicine and Science in Sports and Exercise. Twenty well-trained distance runners increased their training for 6 weeks by adding 3 extra workouts per week. One group (run + run) added running workouts while the other group (run + cycle) added cycling workouts. Both groups improved their 5K times by approximately 28 seconds (from 18:16 to 17:48) after the 6 weeks of increased training. This study is particularly interesting because the runners were more highly trained than those in the other studies and because the increase in training was substantial but realistic. These results clearly show that runners can improve performance by increasing training using cycling workouts. It is likely that other cross-training activities working the large muscle groups of the legs (such as stair climbing, in-line skating, rowing, deep water running, and cross country skiing) would lead to similar improvements, whereas activities less similar to running (such as swimming) would not.
Although the evidence suggests that cross-training can lead to improved performance in moderately-trained or even well-trained runners, there is no scientific evidence concerning cross-training for elite runners. A 1994 review of cross-training studies in Sports Medicine concluded that while cross-training is beneficial for moderately trained athletes, that the principle of specificity of training likely becomes more critical the higher the level of performance.
The Bottom Line
So, what can we confidently say about the benefits of cross-training?
1. Cross-training will help you stay in shape when you canít run. If you cross-train at the same intensity and for the same number of minutes that you would normally run, you will show almost no loss in running fitness for at least 4 weeks, and after that any loss in running performance will be gradual.
2. If you increase your training volume by cross-training you can improve your running performance. The improvement, however, will not be as large as if you had increased your mileage. This point goes right to the heart of the mileage versus injury trade-off. Sure, you would improve more by increasing your running, but you would also increase your risk of injury. The challenge for the runner is to manage that trade-off by running as much as you can before the risk of injury shoots up.
3. There is no evidence that cross training will improve performance in elite runners. The concept of specificity of training becomes more critical the higher the level of performance.