It’s the making of a sports legend: Rajon Rondo, the Celtics’ star point guard, crashes to the floor in the third quarter of a do-or-die game with the Miami Heat in the 2011 playoffs. He dislocates his elbow, but returns to play the fourth quarter, with his left arm hanging limply at his side.

Celtics chief medical officer Brian P. McKeon attributed Rondo’s heroics to the “fight or flight” response, and the endorphins “that help us achieve tremendous things in pain.”

But even in less dramatic circumstances, he said, “part of what makes an athlete an athlete is the ability to play through pain.”

McKeon, an orthopedic surgeon and head team physician, pointed to a recent study from the University of Heidelberg, published in the June issue of the scientific journal Pain, that supports this theory. German researchers reviewed 15 studies that included more than 550 athletes and 330 people with normal activity levels, and found that while most people had the same threshold for pain, athletes had a consistently higher tolerance.

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Brockton High School athletic trainer Jeri Connor (with Lindsay Goms) said that some of the pressure on student athletes to hide injuries comes from parents.

The example set by stars such as Rondo trickles down to amateurs and children, but while soreness and muscle ache are part of athletics, playing through serious pain is never a good idea, said William Levine, an orthopedic surgeon, head team physician at Columbia University, and chairman of the steering committee for STOP Sports Injuries, a national campaign urging awareness of sports overuse and traumatic injuries in children. “Certainly not for student athletes, not for weekend warriors,” he said. “Even in professional sports, it’s almost never a good idea.”

‘Part of what makes an athlete an athlete is the ability to play through pain.’

The cultural message to play through pain is strong, said Dr. Samantha O’Connell, a clinical psychologist in Quincy who specializes in treating athletes and coauthor of a review of research on playing through pain, published in July in Current Psychiatry. It’s not just the professionals who have a championship or a contract at stake who feel the pressure, but high school, collegiate, and even recreational athletes. At every level, she said, persevering and “toughing it out” are part of the sports identity.

It takes about 15 minutes at the athletic trainer’s office in the field house at Marciano Stadium in Brockton to see that even at the high school level, the athletes are regularly playing with or rehabbing from some form of physical pain.

Jeri Connor, athletic trainer for Brockton High School’s sports teams, works at a fever pitch, taping wrists, thumbs, and calves of football, soccer, and volleyball players before they go to the day’s practice. She prescribes stretching exercises to two girls from the soccer team who rehab in her office with Thera-bands, while trying to evaluate the new injuries in students who form a long line at her door.

High school athletes, especially freshmen, can’t always distinguish between the everyday soreness from workouts and practice and serious injury, Connor says.

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Connor (with Neyissa Exilus) has been athletic trainer at Brockton High for 20 years.

One freshman football player complains to Connor that his shoulder hurts. When she gives him a series of strength tests, he can easily resist just about any pressure she puts on his arms in any direction. After making sure his shoulder pads fit property, she sends him back to practice, but with no contact drills. “A minor bruise from hitting drills yesterday,” she deduces.

Meanwhile, another freshman, a running back, arrives with knee pain from the previous week’s practice that he describes as an “8 on a scale of 1 to 10.” He jumps when she touches his knee and admits to playing Monday’s game while in that high level of pain.

As she tests his knee to rule out ligament damage, she admonishes him. “If I can’t touch you without you jumping, do you think one of your friends is going to care where he hits you?”

She determines the knee injury is a bruise of the fat pad underneath the tendon, puts him on a treatment table with an ice pack, and tells him he can’t practice or play until she gives him the OK.

Connor, who has been the athletic trainer at Brockton for 20 years, says that for the most part, coaches listen to her recommendations and understand that putting an injured athlete back into the game too early and allowing an injury to worsen is “shooting themselves in the foot.”

But there will always be student athletes who try to hide their injuries and play anyway, she adds. It’s the nature of an athlete to want to compete.

But the pressure also comes from teammates, and too often, it comes from parents.

“They think their kids are getting a full ride to college or headed to the pros or the Olympics,” Conner says.

High school athletes aren’t the only ones playing with sore body parts, said Don Worden, a former Bruins assistant trainer who is co-owner and clinical director of Pro Sports Therapy, a physical therapy practice in Waltham and Westford. He treats many middle-age women who play through injury in club tennis leagues.

“They say, ‘Hey, I’m on the two spot, my team needs me or we’ll lose our match to the other club,’ ” Worden said, adding that even on a recreational level, many athletes resist advice to sit out games.

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Football and soccer players line up outside Connor’s training room before practice.

Levine, of Columbia, used one of the more common athletic injuries, a mild hamstring sprain, to illustrate the folly of ignoring an injury. Even a mild sprain, a grade-1, produces swelling in the muscle. Viewing the results of a magnetic resonance imaging test of the injury, “it looks like a punch in the arm, a little black and blue,” he said.

If there were no “pop or tear” of the muscle, the athlete might be tempted to play. The risk of playing is progression to a grade-2 injury, Levine said.

“If the injury started as the center of a bull’s-eye, the injured zone has now increased two layers on your dartboard. And that zone continues to expand as you damage more and more muscle,” he said.

With rest, the original hamstring sprain would heal in about a week, while the grade-2 injury requires two to four weeks of recovery. Estimated recovery of a grade-3 injury is three months, Levine said.

He told the story of a runner whom he diagnosed with a stress fracture in her femur, a fairly common injury for long distance runners. This “nuisance injury” is easily reversible as long as the athlete gives it eight weeks rest. But this runner was so determined to compete that she ignored him and ran the New York City Marathon. At around mile 20, the stress fracture turned into a complete fracture. The runner needed immediate surgery that required stabilizing her femur with a metal rod. The recovery time was six to nine months.

“It’s the kind of traumatic injury you usually see from a car accident or a big fall. Doing it to yourself is inexcusable,” Levine said.

There are other problems with playing injured. For example, because the hamstring helps support the knee, the athlete with a sprain might also start straining knee ligaments as he or she tries to compensate. It’s also not uncommon to twist an ankle.

“Athletes need to fluidly and seamlessly do what they do. If they are thinking about a hamstring and worrying about popping it further, they risk injuring something else,” Levine said.

At Joint Ventures Physical Therapy and Fitness, a practice with five locations in the Boston area, owner Dave Larson said that most recreational athletes wait too long before they see the doctor to get treatment.

They might pop ibuprofen to treat the inflammation and continue to play their sport for weeks. The body immediately begins to figure out what it needs to do to stay functional, Larson said.

Without realizing it, a person with an injured hamstring might stop using the hamstring muscle and start to use butt muscles instead. This tendency to compensate creates a whole new layer of physical problems. Besides treating the original injury, the physical therapist has to retrain a patient to fire the right muscles in the correct sequence again.

The longer a patient plays while injured, he said, the longer it takes to retrain the muscles.