When Iñigo San Millán made a career move, from working as a physiologist for professional cycling teams in Europe to his current position at the University of Colorado School of Medicine, he thought he wouldn’t see overtraining in athletes who weren’t professionals.

“Then I opened the door to recreational athletes, and I was like, ‘come on, training 20 hours a week? They’re not going to get overtrained,’ ” San Millán says.

“I was wrong.”

San Millán is the director of sports performance at the new University of Colorado Sports Medicine and Performance Center, which opens next month in Boulder, and one of his areas of expertise is overtraining — a condition for which there isn’t a strict definition in the medical community, but generally refers to a state in which an athlete’s performance is in stasis or decline due to too great of training volume with not enough rest, or improper nutrition.

And it’s not just happening to people training for the longest, most grueling endurance events. San Millán says he’s even seeing it in those training for half marathons.

Overtrained athletes often see clues before they make it to his office for an evaluation, San Millán says. They’re over-fatigued. They might feel burned out. But some recreational athletes expect to feel that way: ” ‘Hey, I’m preparing for a marathon, I’m supposed to be tired,’ ” San Millán says. “But no, you’re not. World-class athletes, they’re not tired. They wake up fresh. If they wake up tired, red lights go off.”

That expectation for being tired speaks to why some of the symptoms of overtraining — especially declining performance — can also spur an athlete to make the situation worse by training harder instead of taking a needed rest day. “You’re working, and you get to a point where your pace is not what it should be. Or, ‘man, I don’t feel that snap.’ So what do people think? ‘Oh, it’s June, I need that intensity,’ and you go to the coach, and he’s like, ‘oh you need more intervals.’ But that’s not true, you need to rest.”

Overtraining is not being exhausted because you’ve done a hard workout, says Rob Pickels, lead physiologist at Boulder Center for Sports Medicine, who also works with overtrained athletes. “It’s OK to be tired from a workout, that’s fine. But when it’s persistent tiredness that spans days, that’s when it’s bad news.”

Fortunately, San Millán says, it’s easy to test athletes by looking for markers of overtraining in a blood test. The first thing he looks at is the blood’s oxygen-carrying capacity by testing hemoglobin levels. Hemoglobin is a component of red-blood cells; we lose red-blood cells every day, but the body produces new ones. Overtraining, however, reduces the body’s ability to replace what we lose. So if San Millán knows what an athlete’s baseline hemoglobin levels are, then sees a decline in those levels after an intense period of training, he can spot overtraining — hopefully before the athlete goes too far down that path — and recommend an appropriate amount of rest.

For that type of testing to work, though, he needs to see an athlete a couple of months before his or her event, to get that baseline. “Don’t wait until the last week, then it’s too late,” he says.

That said, just taking a week off can make a big difference in an athlete’s recovery — and thus performance.

“I’ve had athletes whom I’ve tested who came in a week before a big race, who I’ve said, ‘you should do literally nothing this week before the race,’ ” Pickels says. “And it’s amazing what we see.” They don’t want to take that time off, he says, but it often works.

San Millán says overtraining also results in chronic microtears in an athlete’s muscles. It’s another factor he can test for … and he believes it’s another factor in tendon and joint injuries. “But we can prevent that injury.”

The need for carbs

Nutrition is another component of overtraining that San Millán examines. Endurance athletes need carbohydrates, he says. “The evidence is overwhelming, every single research (study) is showing carbohydrate is critical for performance.” Without carbohydrates, your body can’t top off glycogen stores, which are crucial to high-end performance. “What happens if you do not have enough glycogen, which is what happens to a lot of people? …. We go to reserves, and where does the reserve come from? The muscle. So the muscle starts eating itself to feed itself,” he says.

He’s quick to emphasize that this advice is for more athletic pursuits — for example, runners, not walkers — and that he doesn’t advocate a high-carb diet, because if those carbohydrates aren’t burned, they will turn into fat.

Julian Kyer, a Boulder-based cyclist riding for the SmartStop pro cycling team this year, wasn’t eating enough carbs when he tried going vegan a few seasons ago and fell into an overtraining trap. “I think a lot of endurance athletes, especially cyclists, drastically underestimate their carbohydrate needs,” he says. “When you’re staying on top of it and eating enough and drinking enough on the bike, and refilling those glycogen stores, afterwards, it can be a huge performance boost. You can train harder, you recover better. You aren’t creating that catabolic environment for your muscles when you train really hard.”

He went to see San Millán and adopted his overtraining-avoidance outlook; he looks at training on an almost cellular level now. “It’s been a couple of seasons since I’ve made some of those changes, and it’s made a big difference, it’s made a really big difference.” Kyer placed 11th overall in the USA Pro Cycling Challenge last year.

Signs of overtraining

People who are just walking for exercise aren’t getting overtrained. Neither is someone like a sprinter, who is working very hard while training but isn’t running for long periods of time, says Pickels. “It’s the people in the middle. They’re doing a lot, and they’re trying to do it fast.”

It’s pushing hard for longer periods, not taking rest days and not periodizing (ramping up training over several weeks, then pulling back for about a week once a month for recovery). “People don’t want to take a day, or do intervals,” he says. “They just want to go hard the whole time.”

Periodization helps you peak for an event, but it also helps athletes avoid overtraining, Pickels says. “Every third or fourth week, you really ought to dial it back. Some athletes don’t like it, they don’t think it helps them. And they’re looking at it in a shortsighted manner. Hey, you skip this rest week, the world might not end. But if you keep doing it … you’re going to feel worse.”

Pickels, who works with San Millán and will be joining him at the new sports performance center in Boulder, says he sees plenty of average athletes who are overtrained. And it can manifest in many ways.

“One of the biggest things is a lack of enjoyment in what someone’s doing. Unfortunately we see this a lot in Ironman triathletes. Maybe someone has a trip booked to Cozumel (to race) — it’s a big trip, and a week before the race, they’re like, ‘I don’t even want to ride my bike any more.’ “

But there are other red flags: “Loss of appetite, loss of libido … so one person’s experience will not match everyone else’s,” Pickels says. He’s learned to spot his own indication that he’s overtraining — insomnia. He zonks out early in the evening, but then wakes back up at 1 a.m.

And then there’s stress.

“What’s kind of interesting about overtraining too is that everyone thinks of it as a physical situation, and it’s not necessarily,” Pickels says. “I’ve had athletes who are overtrained from the stress of a death in the family. So you need to look at it in a holistic sense.”

Pickels, a cyclist who coaches a junior mountain biking team, also says there’s a group that gets left out of the overtraining conversation — kids.

“We see, in terms of a percent of the population, we see juniors who are overtrained more than anyone else.”

Junior athletes are busy, he says, and if overtraining isn’t widely known among adult athletes, and it’s even less identifiable for an overscheduled kid.

“It’s hard with them, because they don’t understand — they’re not seasoned athletes.”

Jenn Fields: 303-954-1599, jfields@denverpost.com or twitter.com/jennfields

Opening July 15

The new University of Colorado Sports Medicine and Performance Center, inside the Athletics Champions Center at CU’s Folsom Field, is scheduled to open July 15 and will offer physiological testing for athletes. cusportsmedcenter.com

Use a heart rate monitor? Check for overtraining

Some researchers identify different levels of overtraining. “Overtraining is really a few different stages,” says Rob Pickels, lead physiologist at the Boulder Center for Sports Medicine. “There’s normal, then you go a little beyond normal, which some people are calling overreaching — it’s a little hard on the body, but people are going to be okay. And then we get nonfunctional overreaching — that’s where your results are getting worse and worse … then in overtraining, we are getting a reduction in your adrenal system, your body is holding you back, not letting you hit those higher workloads, and we are starting to see those changes in your body chemistry.”

In the first two stages, you might see an elevated heart rate; if you get more overtrained, it could decrease. “Let’s say you’re at 200 watts (on a bike), and your heart rate is five or six beats over what it should be. When you’re overtrained, the heart rate might drop 10 beats per minute,” he says.

Not sure you’re training enough to worry about it? Once you start hitting 10 hours per week, you have to start paying attention, says Pickels.