The day they're not there is the day she'll retire — and not a day sooner.
At 39, Cummins continues to outrun the biological clock, and late last month was part of a foursome that shattered the Canadian record in the 4x800 metres by 14 seconds at the prestigious Penn Relays. Cummins was part of the team that had set the previous record 10 years earlier.
"This is still something that I love and I'm excited about," Cummins said. "The result still means as much to me now as it did before. And I think that's really important.
"When you can't get motivated or excited to do your warmup the day of competition, then I think perhaps you've lost a little bit of heart in what you're doing. I still get as nervous as I ever did, that has not gone away. I still get nervous of the outcome, which means I still want to run fast. I'm still worried that: 'Oh, what if I don't have a great race today?' All those emotions are still as if this is only my second or third year in competition."
Cummins ran a split of two minutes 2.9 seconds in the relay, teaming up with Melissa Bishop (2:02.2), Karen Belleau-Beliveau (2:03.2), and Lemlem Ogbasilassie (2:06.0) en route to the national record.
Her performance prompted a congratulatory tweet from three-time Olympian Kevin Sullivan, who wrote "Canada's Diane Cummins 2:02 split at Penn Relays at 39yo #ageless."
Cummins is the Canadian record-holder in the 800, running 1:58.39 back in 2001. Twelve years later, she's barely slowed down and last summer raced to 2:00.55 at a meet in Zagreb, Croatia — ranking her first in the world among women aged 35-40, and third in Canada last season.
She has her sights set on a spot on the Canadian team for the world championships this summer in Moscow, which would make her one of the oldest — if not the oldest — woman to ever compete for Canada at the world championships. She'd have to be top-three in Canada to make the team in an event jam-packed with young women.
"There's a new wave of young middle distance runners coming up," said Scott MacDonald, Athletics Canada's high performance director. "But they still have to contend with Diane. She's not done yet."
She finished fourth in the 1,500 metres Saturday at the Jamaica International Invitational, and will be among a star-studded field for Wednesday's Cayman Invitational in the Cayman Islands.
Cummins believes she's part of a wave of women who are deciding to stick with competing after the age of 35.
"I haven't run at my best but I'm still running internationally-recognizable times, and I don't think it's anything that nobody else can do," Cummins said. "As women, we're a lot hardier than people give us credit for. Most of us get distracted and have kids and once you start getting into the real world of having to wake up, or have a job, that just takes away from the whole training.
"It's just been my personal preference not to have a family at this point in my life. Any of my female athletes that I competed against, any of them, if they had chosen to do what I'm doing, I honestly believe they would only be a second or two off their best (times). I think it's just so surprising to people because there's just not a lot of women that do choose to compete after the age of 35 or after they've had a family.
"It's like the first time women ran a marathon, it was like, 'Oh my gosh, there's no way a woman can run a marathon.' Then they stuck us in there and realized 'Gosh, we're damn good.'"
MacDonald believes improving recovery techniques have allowed athletes to compete longer, and points to Ottawa Senators captain Daniel Alfredsson, who's 40.
San Antonio Silver Stars guard Tully Bevilaqua, who turns 41 in July, is the oldest player in the WNBA. Swimmer Dara Torres narrowly missed a spot on U.S. team for last summer's Olympics when she was 45.
Canadian race walker Tim Berrett competed at the 2007 worlds when he was 42, and raced at the Beijing Olympics a year later.
Cummins, who doesn't receive any funding from Sport Canada, said it helps that she has the financial security to train and compete full-time. She races for Mountain West Track Club in Missoula, Mt., and the club provides her with housing, a monthly stipend and travel allowance. She's actually one of the younger women in a training group that includes Canadian Courtney Babcock, who's 40, and is coached by Canadian Vicky Lynch-Pounds.
The 10-time Canadian champion said she can feel her age after a night of not much sleep or a long day spent on her feet.
But she's learned to adjust her training program.
"Obviously there's a lot of figuring out how to handle an older body, and I think slowly now I'm starting to figure it out," she said. "I feel more tension in my body after a speed workout. But now, if I have to take an easy day the next day, I'll just take it.
"I really really have to listen to my body. And I think moreso now than ever, my program changes. I'll get to the track and say, I can't do this. So we change it. When I was younger, I was definitely able to have a month's plan of a program and pretty much do the whole month and not have to switch things too much."
Cummins, Pan Am Games champion in 2007 and a bronze medallist at the 2010 Commonwealth Games, doesn't see herself as a trailblazer so much as just an example of what's possible for athletes who'd like to stick around a little longer.
"I'm not out there thinking: I want to be the first 40-year-old to make the world championship track team," she said. "I think it has to come from your heart. I hope more from an emotional perspective I'm a trailblazer, as opposed to physically I've broken the barriers of what people think is possible for women over the age of 35."
Cummins said barring a major injury — she's only been injured once in her career, a foot problem that kept her off the 2008 Olympic team — she has no immediate plans to call it a career.
"It's all based on the emotions for me. I've spoken to a lot of athletes, and I've said, 'When do you know that the time is right to stop? They've said: 'You'll feel it. You'll know.' I just haven't felt that."