Swimmer Scott Goldblatt grabbed his knee and crumpled to the ground at Stanford University's Avery Aquatic Center on Saturday.
"Yeow," he said. "That didn't feel good."
The 25-year-old member of the U.S. Olympic men's swimming team was in the middle of a punishing regimen of "dry land" exercises alongside Michael Phelps, after two hours of racing Phelps in the pool.
Bob Bowman, who is Phelps's coach, said they try to vary Phelps's training partners, so "nobody gets abused every day."
"It's kind of hard to have the same person race him every day," he said. "It gets kind of demoralizing."
The 10-day training camp for the men's and women's Olympic swimming teams is designed to meld the disparate and competitive personalities of elite athletes into a tight unit before they head to Athens at the end of the month.
It's also aimed at whetting them to their sharpest edge. So they race each other, which means every day someone has to train with Phelps, the world record holder from Baltimore County.
Phelps, 19, said Saturday it has been an honor to race and train with teammates such as Goldblatt, who will swim in the 800 freestyle relay.
Goldblatt said his knee felt better in a few minutes.
Phelps, Goldblatt and the other 41 members of the U.S. Olympic men's and women's swimming teams are gathered here for a brief training camp before the Olympics, which will begin Aug. 13.
Phelps, who holds three world records, arrived right after the Olympic trials earlier this month in Long Beach, Calif. He plans to race in five individual events and three relays in Athens.
He could win eight gold medals. His chief sponsor, Speedo, the swimwear company, has offered him $1 million if he wins seven, which would tie Mark Spitz's record for most gold medals won at an Olympics. Phelps reiterated Saturday that his goal is one gold medal.
Phelps has been blending well with the rest of the team, according to coaches, despite garnering most of the publicity.
"Michael gets what he deserves, and he works for what he deserves," men's coach Eddie Reese said. "He puts it on the line like nobody we've seen."
Last week the men's squad elected veteran swimmers Lenny Krayzelburg and Tom Malchow, both 28, as team captains, snubbing Gary Hall Jr., 29, the oldest member of the men's team, who had publicly said he was hoping for the position.
Malchow, who is on his third Olympic team and who won the gold medal in the 200-meter butterfly at the 2000 Sydney Games, learned last week that he has a torn tendon in his right shoulder.
U.S. swimming officials said that he planned to remain on the team and swim with the injury, but that it could hamper his performance. He was considered a solid silver medal prospect in the 200 butterfly. Phelps holds the world record in the event.
Meantime, Bowman, who also is one of the team's assistant coaches, said Phelps "wasn't anywhere near 100 percent" at the Long Beach trials, where Phelps raced 17 times in seven days, set one world record and qualified for every event he swam.
The coach suggested Phelps could be 20 to 25 percent better in Athens.
But, as with the trials, he will have a heavy workload, potentially swimming 19 races over eight days.
Among his toughest tasks will be the 200-meter freestyle, where he probably will be up against world record holder Ian Thorpe, of Australia, as well as the defending Olympic champion, Pieter van den Hoogenband of the Netherlands, and Grant Hackett, also of Australia.
Phelps's American record of 1 minute 45.99 seconds is well short of Thorpe's 1:44.06.
The Australian media already are touting it as, potentially, one of the greatest races of all time, and Phelps agrees.
"It's going to be fun," he said. "I want to race Thorpe before either one of us are done swimming, in the 200 free. And what better time to do that, standing in front of millions and millions of people on TV watching the Olympics?"
Bowman was coy about the matchup.
"Let's face it, Michael is the overwhelming underdog," he said. "His chances of winning that race are very small. . . . If Michael's anywhere near [Thorpe] it would be a great achievement."
But he added, "I don't think I would put him in a race I didn't think he had a chance to win."