Growing up, I can remember being told that serious dancers should never run, despite the cardiovascular benefits, because the impact is bad for the knees. As it turns out, that might have less basis in fact than we thought.
According to a pilot study recently published in the European Journal of Applied Physiology, running might actually be beneficial for your knees. Rather than wearing down the joints, as is commonly supposed, this study adds to the evidence that running can help prevent chronic issues such as osteoarthritis.
In the pilot study, six healthy recreational runners in their twenties either ran or sat for 30 minutes (the subjects each did both, but on different days). The researchers took blood samples and withdrew small amounts of synovial fluid (the lubricant that helps joints to move smoothly) from the knee joints before and after, looking specifically at indicators of inflammation as well as cartilage oligomeric matrix protein (COMP). Higher levels of these substances in the synovial fluid can be an indicator of or contributor to developing arthritis. With all six subjects, after running for 30 minutes two of the inflammation indicators were significantly lower than baseline, and COMP levels lowered in the synovial fluid.
In other words, a moderate amount of running can cause changes within the knee joints that can help keep them inflammation and chronic injury–free. Of course, this was just a pilot study with a small body of subjects, but it does indicate a new angle from which to study the potential benefits of this particular type of exercise—good news for serious dancers who also enjoy going for a morning run, such as ballerina Arolyn Williams or contemporary dancer Stacy Martorana.
That being said, if you want to add a bit of light running to your cross-training regimen, be smart about it: Warm up and cool down properly, wear supportive, properly fitted shoes, be mindful of your alignment and dial it back if the activity is exacerbating any pre-existing injuries you may have. And if running isn't for you, no sweat: This study is also a good indicator that any motion is better for your joints than being sedentary.
Personally, I'd be curious to see whether the basic small jumps practiced in most technique classes might have a similar effect, provided that they're performed with healthy placement. Get on it, dance science!