JOHN YANG: Officials at Tufts University, outside Boston, are investigating an athletic team workout this month that resulted in nine players being hospitalized, some for about a week.

The incident has put a spotlight on a serious, somewhat rare and potentially fatal muscle condition that can be brought on by overexertion.

Ali Rogin explains.

ALI ROGIN: The condition is rhabdomyolysis, more commonly known as Rhabdo.

When muscles are overtaxed or damaged, they actually start to disintegrate, that releases toxic components of muscle fibers into the bloodstream and can cause kidney damage.

Dr. Miho Tanaka is director of the Women's Sports Medicine Program at Mass General Brigham.

Dr. Tanaka, thank you so much for being here.

You treat many professional athletes.

How common is this condition and who is most at risk?

DR. MIHO TANAKA, Mass General Brigham: Well, this condition is actually quite rare.

So in sports medicine, we hope to not see this, but it absolutely, you know, is a reminder that you know this can happen, even in young, healthy individuals.

ALI ROGIN: And what are the signs if somebody is experiencing this?

MIHO TANAKA: Yeah, so the typical signs that we think about with Rhabdo are having extreme fatigue, having substantial muscle pain, so pain out of proportion to what you would expect after a workout.

And lastly, having darkening of the urine.

So anyone who has any of these three findings after a strenuous workout should consider having medical evaluation.

ALI ROGIN: Very strenuous workouts have become very popular in the United States.

Have there been -- has there been an increase of Rhabdo cases as these types of activities have become more mainstream?

MIHO TANAKA: Yeah.

You know, we have seen these cases reported, especially when they happen in large numbers, as they have in this case.

So when we see teams involved, but you know, we don't actually see the data when it comes to individuals where this occurs, but I think you're exactly right that with these types of strenuous activities and individuals who are just fully capable of pushing themselves beyond their normal limits.

I'm sure that there are cases like this, but the actual numbers, I'm not really clear about in terms of whether the numbers are actually increasing.

ALI ROGIN: I should note that you're not involved in this case.

You don't know the specifics of the incident, but we do know that people on the team disclosed that the person leading the training was an alum, who had just completed Navy SEAL training.

So does that speak to how important it is that whoever's training a group of athletes or individuals know the level of training that they should -- they should not exceed?

MIHO TANAKA: Absolutely.

I think that the most important aspect of training is to make sure that it's individualized to that individual's capabilities and their level of fitness.

And so a fitness plan should definitely incorporate that as well as a progression that's consistent with that individual's ability.

And going way beyond that is when we start to see problems such as injuries or Rhabdo in this case.

ALI ROGIN: There have been a number of these incidents among high school and college athletes.

Why does it seem to happen, particularly in young people?

MIHO TANAKA: I think that there may be a lot of reasons that that this can happen, but probably the number one reason that we typically see is over exertion.

And so when you're given a workout, you're able to push through whatever you're doing, and this is what can lead to this problem.

But there are other sort of risk factors that should be taken into consideration, as well the training environment, so whether it's very hot or very humid, or also internal conditions such as being dehydrated, or substances such as caffeine, stimulants, other types of medications can place people at risk, but I think this sort of a general progression of activities and exercises without clear oversight can lead to overexertion of these young athletes.

ALI ROGIN: And when you're talking to athletes about not pushing themselves too far, what do you say to them?

How did those conversations go?

MIHO TANAKA: Well, I think that you know being aware of your limits is the most important thing, and when you're in a workout, it's very difficult to tell what is too much, because most athletes, again, are able to push themselves through whatever they're given.

And so this is why it's important to take into consideration what you did the week before and where you're trying to go, and working out harder doesn't necessarily get you there faster.

And in general, we try to keep people within about 20 percent of what they did the week prior in terms of the amount that they're increasing, to try to minimize the risk of injury and other medical problems.

ALI ROGIN: Dr. Miho Tanaka, director of the Women's Sports Medicine Program at Mass General Brigham, thank you so much for joining us.

MIHO TANAKA: Thanks very much.