SAN DIEGO — Don Pellmann had been at the San Diego Mesa College track for less than an hour Sunday morning and had already moved his lawn chair twice to remain in the shade, which was receding fast. By the time Pellmann set his fifth age-group world record, in the early afternoon, the temperature on the track was creeping toward 100, which also happens to be the birthday Pellmann recently celebrated.

Pellmann, the most senior athlete in the San Diego Senior Olympics, became the first centenarian to break 27 seconds in the 100-meter dash and the first to clear an official height in the high jump. He also broke records for men in the 100-and-over age group in the shot-put and the discus and set a record in the long jump.

Wearing baggy shorts and a faded red T-shirt with “Donald Pellmann Established 1915 Milwaukee, WI” written across the front, he opened his program by trying to become the oldest man, by roughly nine years, to record a height in the pole vault. He dislodged the bar three times at 3 feet 1 ¾ inches, which gnawed at him the rest of the day.

“I thought I was in better shape,” he said.

The meet volunteers, composed of students from San Diego State’s nursing program and Mesa College’s track team, were awed by Pellmann’s fitness level. They sought him out between his events to express their admiration.

“He’s very, very steady on his feet, and his posture’s very erect,” Sarah Provencher, one of the nursing students, said. “He doesn’t have as much bone and muscle degeneration as others in his age group. You can see he has really maintained his muscles.”

Samantha Foster, 17, a freshman pole-vaulter on the Mesa track team, planted herself so close to the pit that she could hear Pellmann muttering to himself after each of his three vaults. “I love when he says he needs more practice,” she said. “It’s cool to watch him being able to still do this at 100.”

His fellow competitors also sought him out for selfies, including 57-year-old Robert Silva, who said, “You see people that are 100 run, but to see someone that age pole-vault or long jump, that’s another galaxy.”

Pellmann said he had been a gymnast and a high jumper in his youth. The Depression cut short his athletic career at the University of Wisconsin-La Crosse, then known as La Crosse State Teachers College. Pellmann said he quit the track team to get a job. After raising three children with his wife, Marge, who is in her early 90s, Pellmann retired from his job with a General Electric subsidiary in 1970.

At the urging of one of his children, he entered a masters track meet. He did so well that he kept going. “I’ve been in 127 meets since,” Pellmann said.

Before Sunday, two years had passed since Pellmann’s last competition in the pole vault. He used to practice by taking a bamboo stick and jumping into the sandbox at a children’s park, he said, but those days are long gone.

“The only time I can practice is at the meets,” said Pellmann, who lives with his wife, who is ailing, in an assisted living home in Santa Clara, Calif.

He approached the vaulting pit with trepidation, running with a pole he had borrowed from Nadine O’Connor, 73, who is also a record-setting masters athlete. O’Connor and her partner, Bud Held, a 1952 Olympian in the javelin, live outside San Diego and hosted Pellmann, whom they got to know on the seniors track circuit.

Held acted as Pellmann’s coach. In the pole vault, Held urged him to run faster on his approach and consoled him each time he knocked down the bar.

“All you’ve got to do is get a little more speed,” Held said.

Easy for him to say. Held, after all, is a fit 87.

“This is the worst day I’ve had in months,” Pellmann said glumly. He added, “I’m sorry about that pole-vault disaster.”

O’Connor slathered Pellmann with sunscreen, plied him with bananas and tried, mostly unsuccessfully, to get him to drink water so he would not become dehydrated.

“I don’t want to drink too much because that will make me take a trip to the restroom,” Pellmann said.

O’Connor walked off shaking her head. He can be stubborn, she said with a laugh. When she picked him up at the airport Saturday, she said, Pellmann refused a wheelchair and would not let her take the roller bag that he had carried onto the plane.

“He doesn’t take any vitamins, and I couldn’t get him to eat anything last night except fried macaroni and cheese,” O’Connor said.

Pellmann also refused to warm up or stretch, despite encouragement from Provencher. When she told him she was a nursing student, he joked, “I hope I won’t need you,” and remained rooted in his lawn chair.

One of his hearing aids had stopped working, Pellmann said, adding to his misery. “I woke up feeling unwell,” he said. “It could be the traveling. Or it could be old age setting in.”

He added, “At this age, each week it goes downhill.”

To conserve his energy, Pellmann limited himself to one attempt in the long jump, at 5 feet 10 inches, and then retreated to a closet-size training room off the track. Pellmann had an hour to rest before the 100 meters, his main event. He did not bother to take off his shoes, which were falling apart. His left sock poked through a hole he had cut in the shoe to relieve pain caused by a bunion.

Pellmann acknowledged that he had owned the shoes for a long time, but he added, “They’re not quite as old as me.”

He was stretched out on a massage table with his eyes closed when Ardy Riego, an athletic trainer at Mesa College, walked in, introduced himself and offered to give Pellmann what turned out to be his first-ever massage.

While kneading the muscles in Pellmann’s legs, Riego said, “All I can say is his body is still functioning like a normal person’s body, which is amazing.”

Pellmann has not had either knee replaced, and he cannot remember his last injury. “I guess I have pretty good genes,” he said.

Gary MacDonald, the track and field commissioner of the San Diego Senior Olympics, suspects that there is more to Pellmann’s athletic longevity than that. MacDonald poked his head into the training room to check on Pellmann and offer him a bottle of water, which Pellmann waved off.

“Now I know how he got to be 100,” MacDonald said, laughing. “Because he has an attitude.”

As the 100 meters drew nearer, Pellmann grew quieter. “I just hope the massage will help me for my 100,” he said. “The 100 meters is why I came here.”

Pellmann had his sights set on the age-group world record of 29.83, set in 2010 by Hidekichi Miyazaki of Japan. At home, he said, he has marked off 100 meters on Pacific Drive, the road outside his home. At least once a week, he sprints the distance and times himself, he said. The other days, he takes long walks.

“I’ve done it in 26 seconds, so I should be able to break the world record,” Pellmann said.

His heat, which included runners in their 70s, was delayed because a woman in the previous heat fell midway through the race and had to be helped off the track. All of the other runners crouched into the blocks for the start, but Pellmann stood with his hands on slightly bent knees.

At the sound of the starter’s gun, Pellmann took off running. The winner of the heat broke 15 seconds. Pellmann was timed in 26.99.

“That’s what I wanted,” he said.

O’Connor swooped in and guided Pellmann to a spot in the shade. Less than 15 minutes later, she led him to the shot-put area. Pellmann took two throws. His first, which measured 21 feet 6 ¼ inches, counted. It was three feet better than the record. He scratched on the second attempt when he exited the front of the throwing area instead of the back.

Pellmann’s fifth event, the high jump, was delayed because the official setting up the event had to be treated for heatstroke. The temperature was over 90 degrees when Pellmann was driven in a cart used to transport hurdles to the other end of the track, where the high jump was set up.

One of the other competitors, a man in his 70s, was asked how he had practiced for the event. “By jumping onto my bed,” he said.

Pellmann made his first attempt at roughly 2 feet 5 inches. Held had coaxed him to start at that height after Pellmann stated his intention to open at roughly three feet because “if I can’t go three feet, I don’t deserve to be considered for a record.”

He cleared the lower height on his first try and made his second height at 2 feet 11 ½ inches on his third. It was his fourth world record in roughly three hours. One of the other high jumpers patted him on the shoulder and said, “That ties Jesse Owens’s record for world records in a single day.”

At the 1935 Big Ten track and field championships, Owens tied the world record in the 100-yard dash and broke the world records in the long jump, the 220-yard dash and the 220 low hurdles in less than an hour.

Pellmann, who was born two years after Owens, set his fifth world record of the day in the discus. He made three throws and improved his distance each time, ending with a throw of 48 feet 9 inches.

After his final attempt, he clung to the netting around the throwing area while catching his breath. Then he returned to his lawn chair and allowed Riego to apply a bag of ice to the back of his neck.

Pellmann asked O’Connor if she would collect his gold medals. “I’ve had enough,” he said.