As if their record-breaking, medal-winning performances weren't inspiring enough, a number of the top Olympians at this summer's Games have overcome life-altering obstacles to reach the podium.

Many of these challenges have presented in the form of health problems and conditions that are difficult enough on their own, without the added pressure of competing on a global stage.

But that hasn't stopped these Olympians. Here's a look at how some of London’s stars have succeeded in the face of illness.

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  • Eric Shanteau

    At only age 24, just a week before the Olympic Trials for the 2008 Games in Beijing, the American swimmer faced what he has called <a href="http://www.huffingtonpost.com/2012/08/01/eric-shanteau-olympic-swimmer-cancer-survivor_n_1727894.html" target="_hplink">a "devastating" diagnosis</a>: testicular cancer. He was able to postpone treatment until after competing in Beijing; he had surgery to remove the tumor in August and has been cancer-free since, BSU reported. After becoming involved with the LIVESTRONG Foundation, Shanteau then started <a href="http://shanteauopenwater.com/" target="_hplink">Swim For Your Life</a>, an awareness-raising event now in its third year. All proceeds <a href="http://shanteauopenwater.com/about-2/" target="_hplink">benefit the programs and services of the Lance Armstrong Foundation</a>, according to the Swim For Your Life website. Shanteau made it to the semi-finals in the <a href="http://www.nbcolympics.com/swimming/event/men-100m-breaststroke/phase=swm031200/doc=summary.html" target="_hplink">men's 100-meter breaststroke</a>, and will compete in the <a href="http://www.nbcolympics.com/athletes/athlete=eric-shanteau/index.html" target="_hplink">men's 4x100-meter medley relay on Friday</a>.

  • Dana Vollmer

    On Sunday, the 24-year-old American swimmer became the <a href="http://well.blogs.nytimes.com/2012/07/31/overcoming-a-heart-condition-to-win-olympic-gold/" target="_hplink">first woman ever to swim the 100-meter butterfly in under 56 seconds</a>. But when she was just 15, Vollmer was <a href="http://www.huffingtonpost.com/2012/07/27/dana-vollmer-heart-condition_n_1711515.html" target="_hplink">diagnosed with long QT syndrome</a>, an electrical disorder of the heart that could lead to sudden cardiac arrest, Everyday Health reported in a recent profile of the swimmer. While many athletes with similar conditions are sidelined by their health, Vollmer was allowed to continue swimming, provided an external defibrillator was nearby every time she hit the pool. Today, it seems Vollmer has outgrown long QT -- doctors can't find any signs of the syndrome, Everyday Health reported. "It's amazing... to be healthy and really enjoying the sport again," she told the site. Along with mom Cathy, Vollmer <a href="http://bleacherreport.com/articles/1277879-dana-vollmer-olympic-gold-medalist-has-the-heart-of-a-champion" target="_hplink">volunteers for the American Heart Association</a>, giving speeches and making appearances to help raise awareness around heart disease, according to Bleacher Report. Now that she's got her gold, she'll also compete in the upcoming 4x200-meter freestyle relay.

  • Jake Gibb

    The American beach volleyball player was flagged for abnormal hormone levels by a drug tester -- the reason, it turned out, was that <a href="http://www.washingtonpost.com/sports/us-beach-volleyball-player-jake-gibb-recovers-from-cancer-to-make-olympics-_-twice/2012/07/30/gJQAduOiKX_story.html" target="_hplink">he had testicular cancer</a>. Doctors were able to successfully remove the tumor, meaning Gibb didn't need chemotherapy and could return to the beach with enough time to qualify for the 2012 Games, where he and partner Sean Rosenthal <a href="http://www.london2012.com/beach-volleyball/event=beach-volleyball-men/" target="_hplink">continue to compete</a>. "I realized the things that matter most to me, and that's health and family," he said of the experience <a href="http://www.jakegibb.com/" target="_hplink">in a video on his website</a>.

  • Carrie Johnson

    In 2003, when she should have been training for her first Olympics, the American kayaker was struggling with stomach symptoms doctors couldn't quite put their fingers on. "It started with symptoms of fatigue and it kind of escalated to increasingly worse GI symptoms," she told <em>USA Today</em>. Six months later she was <a href="http://www.usatoday.com/sports/olympics/london/canoe/story/2012-06-06/carrie-johnson-modifies-training-crohns-disease/55480360/1" target="_hplink">diagnosed with Crohn's disease</a>, the paper reported, a <a href="http://www.mayoclinic.com/health/crohns-disease/DS00104/" target="_hplink">chronic inflammatory bowel disease</a>. While navigating treatment options -- "It's basically a trial and error process," she has said -- she has been able to compete in both the 2004 and 2008 Games, and will kayak in the <a href="http://www.london2012.com/athlete/johnson-carrie-1133421/" target="_hplink">200- and 500-meter events in London</a>. Her health problems may have actually <a href="http://articles.latimes.com/2012/apr/29/sports/la-sp-oly-canoe-kayak-johnson-20120430" target="_hplink">given her a special perspective</a>, she told the <em>L.A. Times</em>. "Having to take time off made me realize how much I wanted to be doing it," she said. "Now, if I'm having a bad practice or a bad day, I have that extra appreciation."

  • Venus Williams

    In 2011, the elder Williams sister was <a href=" http://espn.go.com/olympics/summer/2012/tennis/story/_/id/8217492/2012-london-olympics-venus-williams-maria-sharapova-win-advance-third-round" target="_hplink">diagnosed with Sjögren's syndrome</a>, an autoimmune disorder that causes fatigue and aching muscles and joints, and took a break from tennis for a while. "<a href="http://www.nytimes.com/2011/09/02/sports/tennis/2011-us-open-venus-williams-describes-fights-with-fatigue.html?ref=tennis" target="_hplink">The fatigue is hard to explain</a> unless you have it," she told <em>The New York Times</em> shortly after her diagnosis. "Some mornings I feel really sick, like when you don't get a lot of sleep or you have a flu or cold. I always have some level of tiredness. And the more I tried to push through it, the tougher it got." Appearing rejuvenated at the start of the London Games, Williams advanced to the third round before <a href="http://www.latimes.com/sports/olympics/olympicsnow/la-sp-on-serena-williams--federer-venus-20120801,0,1607963.story" target="_hplink">losing to Germany's Angelique Kerber</a> on Wednesday.

  • Phil Dalhausser

    In June, the American beach volleyball gold medalist spent three days in the hospital and a month on a blood thinning medication as part of <a href="http://www.usatoday.com/sports/olympics/london/volleyball/story/2012-07-30/todd-rogers-phil-dalhausser-beach-volleyball/56588660/1" target="_hplink">treatment for two blood clots</a>, he recently revealed to <em>USA Today</em>. <a href="http://www.mayoclinic.com/health/blood-clots/MY00109/DSECTION=causes" target="_hplink">Blood clots</a> that form in deep veins can block blood flow or break free and travel through the blood stream to the lungs or brain, the Mayo Clinic explains. Dalhausser and partner Todd Rogers continue to compete in London, set on repeating their gold-medal performance from Beijing, they told <em>USA Today</em>.

  • Paula Radcliffe

    She may be the female world record holder in the marathon, but Radcliffe hasn't won a single Olympic medal in four Games -- and she's now officially out for London, as well. The long-distance runner was <a href="http://www.bbc.co.uk/sport/0/olympics/19035570" target="_hplink">declared unfit to compete</a> due to a foot injury, the BBC reported. But she's continued running despite another health concern since she was a teenager: asthma. "<a href="http://www.health.com/health/gallery/0,,20306639_5,00.html" target="_hplink">I always take my reliever inhaler before and after I run</a>, and am extra careful when I have a cold, as that can make the symptoms more severe," she has said, Health.com reported. And she told the BBC, "Asthma didn't stop me doing what I love." While it might seem like a condition that makes sports infinitely more difficult, around eight percent of Olympic athletes have asthma, making it the <a href="http://www.sciencedaily.com/releases/2012/07/120731094613.htm" target="_hplink">most common chronic disease</a> among these star athletes, a recent study found.

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