An important pillar in the field of sports and exercise science is the principle of specificity. It says that for optimal performance in a sport, training should be very specific to that sport. Which means if you want to become a fast runner, you have to do a lot of running. Cross-training on the other hand is all about mixing up your sports and has a number of benefits as well. Adding some strength training to your workout could lead to a better performance in your sport and if your goal is recovery from or prevention of injury, fighting boredom, or just overall fitness, cross-training can be a good solution.
In a frequently cited review on cross-training from 1994, Hirofumi Tanaka, an exercise physiologist at the University of Texas in Austin, showed the principle of specificity in action. The studies in his review compared running, cycling and swimming. The review showed that athletes’ VO2max (their maximum ability to consume oxygen – an indicator of physical fitness) usually was highest in the sport they had trained for. Tanaka did find some transfer of VO2max from one sport to another, especially between running and cycling for non-elite athletes (very little for swimming) but the cross-training effects never exceeded those induced by the primary sport. Since his review, more transfer of training effects have been found, giving cross-training a bit more credit, but the principle of specificity is still strong.
Richard Godfrey, physiologist at the Centre for Sports Medicine and Human Performance of Brunel University in London, also wrote about the subject in 2006. He argued that there are three components of specificity that should be targeted during training: the right energy system, the right muscle groups and the right skills.
And when targeting these components, the more specific, the better. For instance, a review of strength training in the mid 1990s showed that when exercising certain muscles, the specific velocity, range of motion, joint angle and type of contraction (muscle shortening, lengthening or staying the same length) all influenced a training’s effectiveness.
And even more components of specificity beyond Godfrey’s three might be worth considering. Take for instance the time of day that people train. In one study at the University of North Texas, 12 college-age women did high-intensity cycling either in the morning or the afternoon. In subsequent tests, the women who had trained in the morning performed best if their test was also in the morning and the women who had trained in the afternoon, performed best on afternoon tests.
In another study at the University of Tehran in Iran, an effect of arousal specificity was found. Before practicing basketball free throws, researchers put 37 male students in either a high or low state of arousal by selectively using motivational techniques like pep talks, the presence of spectators, competition elements and rewards. Afterwards the students were tested in both states of arousal which revealed that the students performed best in tests with an arousal level that matched the one of their practice sessions.
Why Then Do Cross-Training?
Despite the clear merits of the specificity of training, it could still be worth it to extend your training regiment with some other activities. For instance, according to a 2008 study conducted in Norway, it turns out that runners can become more efficient with strength training. Researchers took 17 well-trained runners and had half of them supplemented their normal endurance training with short maximum strength training sessions. The strength training consisted of performing half-squats with weights (bending the knees to 90 degrees) and was done in four sets of four, 3 times a week , for 8 weeks. After this time, runners with the training supplement had, besides stronger legs, improved their running economy (a measure of how efficiently they used oxygen while running) by 5% and time to exhaustion by 21% while the runners without strength training showed no improvement. Similar benefits of strength training have been found among soccer players, cross-country skiers and cyclists.
Cross-training can also be useful when an athlete is injured. It can be a way of staying active and a way ‘to slow down the rate of loss in fitness,’ according to Richard Godfrey. In a 1998 article on cross-training, he wrote that, for instance, deep-water running could be used to maintain some level of running-specific muscle strength and cardio-respiratory functioning. Later studies substituted running with a few weeks of cycling or using an elliptical trainer (a stationary exercise machine) and found that participants maintained their VO2max.
Godfrey argued that cross-training could also play a role in the prevention of overuse-injuries. Studies in 1992 and 1998, involving trained runners, showed that adding bike-training to a run-program for a few weeks, caused the same improvement in running performance as extra running did but obviously without the extra pounding of the legs.
What Do Athletes Do in Practice?
There are few statistics on how much people cross-train in practice but it could actually be quite a popular activity. Runner’s World, the world’s largest running magazine, had a poll on its website earlier this year which found that out of about 3,000 runners that responded, 70% did some form of cross-training each week.
Professional coaches also clearly see some benefits. When asked about how much cross-training he does, Gerard Kemkers, coach of the Dutch TVM speed skating squad, which includes world champions like Sven Kramer and Ireen Wüst, laughs: “We hardly do anything else,” he said, “The whole Summer we cross-train. We bike a lot, we do much strength training, we do a lot of inline skating, so we are working on many forms of movement with the goal of becoming better speed skaters.”
Besides the fact it is hard to speed skate in the Summer, Kemkers has more reasons. The former physical education teacher and Olympic medalist explained: “If you want to reach the pinnacle of a sport, you need a broad development in my opinion. The principle of cross-training during the build-up of someone’s career I think is very helpful. It stimulates the development of broader motor skills which can be useful later at the top.”
And there is a mental aspect. “In speed skating we experience that the variety of having a summer and a winter season is very motivating. At the end of the winter we are done skating and everyone longs for the bike; at the end of the Summer everyone wants to skate again. It keeps a sort of freshness to the system,” he said.
Brian Farley, coach of the Dutch national baseball team who became world champions last year in Panama, also strongly believes in cross-training, especially for the development of athleticism in young players. “Certainly until the age of 16 or 17 years old, we definitely encourage our players to play more than one sport and preferably two other sports,” he said. “Baseball is a very unilateral sport. We swing and we throw in one direction so we are underdeveloped on the other side of our body. So we need to have another sport, similar to football or basketball, that requires those kinds of skills.”
Perhaps not all these viewpoints have been supported by science yet, but these coaches clearly had great success training their athletes.
And what if you don’t need to become world champion in your sport and your goal is just overall fitness and general health? Then cross-training fits the bill as well. Influential health advice from the American College of Sports Medicine last year included doing some cardio-respiratory exercise, exercising the major muscle groups, and exercising balance, agility and flexibility. These are things that a nice mix of sports could provide.
Godfrey, R. J. (1998). Cross-training. Sports Exercise and Injury. 4:50–5
Godfrey, R. J., & Whyte, G. (2006). Training specificity. In G. Whyte (Ed.), The physiology of training (pp. 23–43). Amsterdam: Elsevier