Judi Brown Clarke, a silver medalist in the 400-meter hurdles at the 1984 Los Angeles Olympics who went on to coach at Michigan State University, witnessed young athletes who fell apart as their controlling parents pushed them to the limit.
"I have seen athletes who wanted to please their parents so much -- this extra pressure to perform made them anorexic or bulimic," said Clarke, now 51.
Behind every Olympic athlete is a parent (or two) who have encouraged and pushed their child through tens of thousands of hours of grueling training to keep them on track.
Jim and Cecille Adrian watched their 23-year-old son Nathan qualify for the 100 meters freestyle with the fastest time in the preliminary rounds.
"Driving about 100,000 miles in four years, taking vacations in about 15 different cities in the US, probably 100,000 air miles -- and that's just the start," Jim Adrian told ABC News. "It wasn't cheap, but it was worth it. It's a good investment. You always invest in your kids."
For Les and Cathy Volmer, parents to 100 meter butterfly gold medalist Dana, their daughter's success as a junior swimmer convinced them to keep supporting her – despite the missed vacations and long hours.
"The cost of it all -- you had to look ahead and say, I don't want to say is she worth spending the money on – [but] are we pointing in the right direction, are we putting our money in the right direction?" Les Volmer told ABC News. "As long as she kept giving us information with her smiles, her talent, her coaches talking to us about yeah, she can make the next level – then it was always worth it. And it got expensive but there was always a success in sight. So we kept going on."
Sports psychologists and even the athletes themselves recognize that parents need to balance their control so their children can be winners, but not losers in life.
Clarke feels so strongly about the issue that she contacted Rita Wieber to guide her before 17-year-old Jordyn Wieber's disappointing gymnastic performance in London.
"I wanted to give her insight into what it looks like from the athlete's perspective to be a parent -- where is the line of control," said Clarke, who is now director of diversity at the National Science Foundation Center for Science and Technology at Michigan State University.
"I sometimes find that it's not the parents who have had success, but the parent who had a frustrating career and vicariously see their child as their second chance," said Clarke. "They see it as a personal accomplishment instead of the child's accomplishment."
Most athletes' parents never step over healthy boundaries, according to Dan Gould, director of the Institute for the Study of Youth Sports at Michigan State University.
But according to a study on coach perceptions, three out of 10 parents may cross that fine line "unknowingly," and one in 10 will actually be "high maintenance."
"They are critical with the child or lose emotional control," said Gould. "Sometimes they try to coach when they are not trained as a coach or walk off the court with a lot of drama."
He and his colleagues studied the long-term outcomes of Olympic champions in a paper published by the Association of Applied Sports Psychology.
"We know parents in general influence kids in a lot of ways," he said. "If the parent places more importance on winning that tends to create more stress."
Their research has shown that parental pressure can also backfire, hurting an athlete's development. Some "burn out" or leave the sport altogether.
The average athlete gives 10,000 hours of "deliberate practice" to develop the expertise to go all the way to the Olympics, according to Gould. "They do it with some yelling and pushing, but in the end, you push yourself."
"Even well-meaning parents can get really caught up in five-ring fever," he said. "You can't use guilt to motivate a kid or love withdrawal."
Gould says it's a "delicate balance." The best parent will ask their children to "follow through on your commitments and the responsibility of good practice."
No parent-child relationship is ever going to be completely "normal" at this level of competition, according to Gould.
Larry Lauer, who is director of coaching education and development at the institute, did a study on the influence of parents on nine professional tennis players.
Athletes with controlling parents thought about quitting at some point in their junior careers. "Those who carried forward decided to play tennis for themselves and not for their parents," he said.
One top-ranked female player told researchers, "My mom would rather have me win a tournament than come home to see her."
When he looked at athletes and their parents over time, the most demanding parents had "strained relationships" with their children.
"When people are constantly under stress it causes them to make other choices to relieve that stress, like drinking and taking drugs or even promiscuity," said Lauer.
As for former Olympic medalist Clarke, she tries to strike a balance with her three children, including 15-year-old Antonio, who is a rising high school basketball and track star.
"I try not to get over-involved," she said. "I used to coach professionally and that kicks in -- and it's a fine line between being a coach and a parent. Intrinsically, they have to see the sport as their core value in their life, otherwise there is resistance when a parent is always pushing them."
"I had to not use my personal drive and how I see sports and impose that on my kids," said Clarke. "They had to figure it out for themselves."