Story highlights U.S. runner initially hurt leg on a staircase 
 
 At 200 meters in Thurday's race it snapped 
 
 He still ran 46.1 for one lap 
 
 The U.S. rallied to finish second in its heat 
 
 Just after the U.S. team finished second in its 4x400-meter relay heat, a limping Manteo Mitchell told reporters his injury was nothing serious. 
 
 "It might be a simple cramp," he said. 
 
 Turns out it was a lot more than that. 
 
 Mitchell broke a bone in his left leg, USA Track and Field said in a news release. The 25-year-old, running the leadoff leg, felt his fibula snap with 200 meters to go. He had to finish or the United States would have been out of the event. 
 
 JUST WATCHED The guy who will close the London Games Replay More Videos ... MUST WATCH The guy who will close the London Games 02:19 PLAY VIDEO 
 
 Olympics live blog 
 
 "I wanted to just lie down. It felt like somebody literally just snapped my leg in half," he said. 
 
 For a half-lap he ran in excruciating pain until he handed off to Josh Mance. 
 
 Mitchell's split was 46.1 and the Americans went on to finish in 2:58.87 to qualify for Friday's final. 
 
 Mitchell said on Monday he was going up a set of stairs, missed one and landed poorly. 
 
 "I got treatment and I was fine," he said, adding that he felt good warming up for Thursday's race. 
 
 An X-ray taken Thursday after the relay showed the break. 
 
 He seemed to have good spirits about it. 
 
 "Never thought that the phrase 'break a leg' would reach reality for me lol," he tweeted later. 
 
 USA Track and Field has not said who will take Mitchell's place on the team. Two other members of the relay team pool -- Jeremy Wariner and LaShawn Merritt -- have injured hamstrings and cannot run. 
 
 The Americans will likely turn to one of their 400-meter hurdlers. Angelo Taylor, who was fifth in the 400 hurdles, ran in the 4x400-meter relay final at the world championships last year. Kerron Clement ran for the U.S. at the Beijing Games. But that was in a qualifying race while Taylor ran in the final, winning gold. 
 
 Bolt makes history ||||| Photo by Feng Li/Getty Images. 
 
 "I heard it and I felt it," American sprinter Manteo Mitchell told the Associated Press after breaking his leg on Thursday. Mitchell, who was halfway through his segment of the men’s 4-by-400 relay when he felt something snap, did what he said “almost any person would've done in that situation”—he finished the remaining 200 meters. His endurance wasn’t for naught: After Mitchell limped off, his three teammates completed the relay and qualified for the 4-by-400 final. After the race, doctors diagnosed Mitchell with a complete break of the left fibula and said the bone would heal in four to six weeks. How difficult is it to run 200 meters on a broken fibula? 
 
 Very difficult, but not impossible. The fibula is the smaller of the two bones that make up the lower leg, the other being the tibia. Unlike the tibia, the fibula is non-weight-bearing. As such, it is possible to run on a broken fibula. The pain, though, would be intense and would likely debilitate many athletes. The fact that Mitchell made it around the track in just more than 46 seconds—a time that placed him in a tie for fifth out of eight runners—is extremely impressive. 
 
 Advertisement ||||| The United States continued its surge up the Olympic medal rankings Friday with a record-breaking victory in the women's 4x100-meter relay. 
 
 Ethiopia's Meseret Defar holds up a picture to her face after she won gold in the women's 5000-meter final during the athletics in the Olympic Stadium at the 2012 Summer Olympics, London, Friday, Aug.... (Associated Press) 
 
 FILE - In this Aug. 18, 2004, file photo, Tyler Hamilton holds up his gold medal after the men's road individual time trial of the 2004 Olympic Games in the outskirts of Athens. The IOC is set to formally... (Associated Press) 
 
 United States' women's 4 x100-meter relay team members, from left, Carmelita Jeter, Bianca Knight, Tianna Madison and Allyson Felix, celebrate their gold medal win during the athletics in the Olympic... (Associated Press) 
 
 Ethiopia's Meseret Defar reacts as she crosses the finish line to win the 5000-meter final during the athletics in the Olympic Stadium at the 2012 Summer Olympics, London, Friday, Aug. 10, 2012. (AP Photo/Anja... (Associated Press) 
 
 Jamaica's Usain Bolt celebrates winning the gold medal in the men's 200-meter final during the athletics in the Olympic Stadium at the 2012 Summer Olympics, London, Thursday, Aug. 9, 2012. (AP Photo/Matt... (Associated Press) 
 
 Ethiopia's Tirunesh Dibaba, right, and Ethiopia's Meseret Defar compete in a women's 5000-meter heat during the athletics in the Olympic Stadium at the 2012 Summer Olympics, London, Tuesday, Aug. 7, 2012.... (Associated Press) 
 
 Turkey's Asli Cakir Alptekin celebrates her gold medal in the women's 1500-meter during the athletics in the Olympic Stadium at the 2012 Summer Olympics, London, Friday, Aug. 10, 2012. Bulut won the silver... (Associated Press) 
 
 Venezuela's Omart Longart, left, and South Africa's Oscar Pistorius, center, wait for the batons during the men's 4x400-meter relay final during the athletics in the Olympic Stadium at the 2012 Summer... (Associated Press) 
 
 The crowd cheered wildly as Carmelita Jeter crossed the line as the clock marked 40.82 seconds _ well below East Germany's 41.37 record from 1985. Teammates Tianna Madison, 200-meter champion Allyson Felix and Bianca Knight gave the U.S. a big lead heading into the anchor leg by 100 silver medalist Jeter. 
 
 "I was already pointing at the clock, saying 'there it is!'" Jeter said after the race. "There was a cloud hanging over us with people saying 'they cannot do this, they are going to drop the stick,' but we did it." 
 
 Heading into the final weekend of the London Games, the U.S. tops both the gold and overall medals races after trailing the Chinese for most of it. 
 
 It was yet another remarkable night in the main Olympic stadium as double amputee Oscar Pistorius of South Africa ran his last race of these Olympics in the men's 4x400-meter final. The U.S. just missed that gold, however, which went to the Bahamas. Pistorius _ the first amputee runner in track and field to compete at the Olympics _ received the South African baton in last place and was last crossing the line. 
 
 The man known as "Blade Runner" because of his prosthetic carbon fiber blades came close to not running at all Friday after a Kenyan runner on Thursday knocked over South Africa's Ofentse Mogawane on the final bend in the second leg of the race. 
 
 But the judges later ruled that the Kenyan runner had cut across Mogawane, causing the collision, and advanced the South African team to the final anyway. 
 
 In other track finals, an Olympic record was set as France's Renaud Lavillenie won the pole vault gold medal with a games mark of 5.97 meters. 
 
 In the women's 5,000 meters, Meseret Defar beat fellow Ethiopian Tirunesh Dibaba to win the gold. Defar, the 2004 Olympic champion, overtook Dibaba in the final stretch and took the gold medal in 15 minutes, 4.25 seconds. 
 
 Later, Asli Cakir Alptekin of Turkey also crossed the line ahead of her teammate Gamze Bulut to win the gold medal in women's 1,500-meters. European champion Alptekin, who served a two-year suspension for doping after the 2004 world junior championships, won the gold medal in 4 minutes, 10.23 seconds. 
 
 Russia's Tatyana Lysenko earned a gold in women's hammer throw. 
 
 Away from the track, the Netherlands had a 2-0 win over world champion Argentina to hold on to their women's Olympic field hockey title. In the bronze medal match, Britain won its first women's field hockey medal in 20 years with a 3-1 victory over New Zealand. 
 
 Earlier Friday, Mathew Belcher and Malcolm Page of Australia held off their British rivals to win the men's 470 class, the country's third on the English Channel at Weymouth, ensuring that the Australians will finish with more sailing golds than Britain. 
 
 "I suppose I am an old man now," the 40-year-old Page said. "I have been campaigning in 470s for 15 years. To go out like this is incredible." 
 
 Sailing is just about the only place where Australia is excelling, particularly over the host country. After surprisingly winning just one gold medal in the swimming pool _ in a women's relay _ the games were an early disappointment for a team hoping to finish in the top five in the gold medal race. 
 
 They won't achieve that, but gold medals to 100-meter hurdler Sally Pearson and cyclist Anna Meares, along with the triple gold performance from its sailors in the past five days have taken some of the sting out of what has been an under-par games for Australia. 
 
 Most depressingly for Australia, its seven gold medals overall have been dwarfed by the 25 _ and counting _ won by their traditional and often bitter sporting rivals from Britain. 
 
 In a later race at Weymouth, Australia's trans-Tasman neighbor New Zealand won gold in the women's 470 class. Jo Aleh and Olivia Powrie clinched the Kiwis' second sailing medal and fourth overall. 
 
 Maris Strombergs of Latvia won his second straight Olympic gold medal in BMX, taking the lead out of the starting gate and never relinquishing it. Strombergs won the inaugural competition at the Beijing Games, but has struggled with injuries the past of couple years. 
 
 Carlos Mario Oquendo Zabala made it a good afternoon for Colombia with his bronze. His teammate Mariana Pajon _ the flag bearer for Colombia in the opening ceremony _ won gold in the women's race earlier in the day. 
 
 Squel Stein of Brazil crashed heavily during the semifinals of the race and was carried off the course on a stretcher. 
 
 At a murky Serpentine Lake in London's Hyde Park, Ous Mellouli showed his versatility in the water, winning the 10-kilometer open water race less than a week after taking bronze in the 1,500 in the Aquatic Centre pool, the first swimmer to achieve that feat at the same Olympics. 
 
 It was the second gold of Mellouli's Olympic career, having won the 1,500 at the 2008 Beijing Games. 
 
 He overcame shoulder and elbow injuries before the games, plus a virus two days ago. Now, he's considering retirement. 
 
 "Only those close to me know how much I struggled to get here today," Mellouli said. "I don't think there's a better way to go out than this. I can just leave it all behind and have no regrets." 
 
 Russia won the synchronized swimming team final, giving the country its fourth consecutive gold medal in the event. China and Spain took the other podium spots, leaving Japan without a medal in synchro swimming for the first time since the sport was added to the Olympics in 1984. 
 
 ____ 
 
 AP sports writer Dennis Passa contributed to this story.
– The US made it to the men's 4x400-meter relay finals with the help of a runner who deserves a gold medal for pain endurance. Manteo Mitchell was 200 meters into the race's first leg when a bone in his leg snapped. He managed to finish the rest of the lap in excruciating pain, and keep the US in the competition, CNN reports. After he limped off, an X-ray confirmed that the 25-year-old athlete had a broken left fibula, the smaller of the two leg bones. It is possible to run with a broken fibula, but most people would find the pain unbearable, Slate notes. Mitchell originally hurt himself missing a step as he went up some stairs at the Olympic Village earlier in the week, but he says he felt fine after treatment. But "as soon as I took the first step past the 200-meter mark, I felt it break. I heard it," he says. "I even put out a little war cry, but the crowd was so loud you couldn't hear it. I wanted to just lie down. It felt like somebody literally just snapped my leg in half." The US—which has won gold at the eight Olympic 4x400-meter relays it entered—now advances to tonight's final, although the team has not yet announced its replacement for Mitchell.