Is cross-training beneficial? Yes, if you are a recreational athlete. If you are a professional, it will only help you when the other sport is resistance training.
What Is Cross-Training?
The theory behind cross-training is that you have a primary endurance activity you want to get better at and have a certain weakness when performing it. Cross-training theory supposes you can address it if you pick up an activity where you don't have that weakness.
For example: you are a long-distance runner and if you want to get better at running. Your coach tells you to pick up cycling. The cycling, he says, will alleviate your running weakness and your running will be better.
For Pros It's Equal At Best
There exists a lot of anecdotal evidence for the existence of this positive effect and very many coaches still advise athletes to do cross-training. But the scientific results are far more mixed, especially where it concerns professional athletes.
Already in 1994 Dr. Hirofumi Tanaka from the University of Austin, Texas, did a meta-analysis of studies looking at the supposed beneficial effect. He found that when it comes to performance in endurance activities, cross-training's effects at best don't exceed those of sport-specific training.
Combining With Resistance Training Is Better
Things look different when your primary sport is in the endurance field and you combine it with resistance training.
Dr. Tanaka also did an analysis of runners, cyclists and swimmers who coupled their sport with weightlifting. Running and biking both benefitted, while swimming did not. The reason may be that swimmers would need to perform resistance training in water, mimicking their movements there.
But's that just a guess. Nobody knows why weightlifting improves performance in the other two. It could be that weightlifting trains supporting muscles in the legs and runners and cyclists can use them as backups when their main muscles tire.
For Recreational Athletes Cross-Training Is Fine
If you are a professional athlete, put the focus of your training on your main sport, add some resistance training to your weekly regime and gauge your mileage.
If you aren't into competitive sports, follow the recommendations of the American Orthopedic Society for Sports Medicine and the American College of Sports Medicine: do cross-training. It will offer you the best overall fitness possible, while avoiding boredom and getting injuries from doing specific movements for too long and too often.
Picture courtesy of Mike Baird.