Faith Kipyegon is really, really fast.
In 2023, the Kenyan middle-distance runner set three women's world records, including running a blistering 4:07 for the mile, breaking the previous record by five seconds.
Track fan and biomechanist Rodger Kram was watching that race, and something about how it played out stuck with him.
"The runners who were her pacemakers ran out too fast and there was a gap between her and her pacemaker," he says.
Pacemakers help set a fast pace, and act as a barrier to the wind, making the race easier for the runners behind them — but only if they're close.
"So she really had pretty poor aerodynamic drafting when she broke the record," says Kram, of the University of Colorado Boulder. "That got us thinking that maybe if we improved drafting and reduced the force that the air exerts to slow you down, whether she could break 4 minutes."
Kram and his colleagues are no strangers to such schemes. They predicted, and then helped plan, Eliud Kipchoge's sub 2-hour marathon in 2019, where he was precisely paced to 1:59:40 by a rotating team of runners who ran in front of him for most of the race. That setup helped Kipchoge run faster than anyone ever had, and his colleagues wanted to see if something similar could work for Kipyegon.
Theoretically, it could. With pitch-perfect pacing both in front of and behind Kipyegon, she could run 3:59 for a mile, researchers reported this week in the journal Royal Society Open Science.
"I'm sure people are going to say no way, women can't run under four minutes," says Kram. But he notes that people thought it was physiologically impossible for men to run that fast until Roger Bannister did in 1954.
Predicting sub-four
On a basic level, running requires burning energy to power forward movement. How much of that energy gets translated to forward motion depends on a variety of factors, from running form to wind resistance. Kipyegon's form is already near-perfect, but drafting behind a pacer could allow more energy to go towards running fast.
To figure out how much faster Kipyegon could run, they first calculated how much energy she burned for each lap of her record-setting mile. Then, they used aerodynamic models to calculate how much faster she could run with drafting.
"We looked at several different formulations of drafting," says Shalaya Kipp, a biomechanics researcher now at the Mayo Clinic. "One scenario was if she ran in a vacuum, with no air resistance at all."
In that hypothetical scenario of 100% drafting effectiveness, Kipyegon could run 3:53, the researchers found. The researchers considered more realistic scenarios, where Kipyegon had pacers for two, three and four laps.
The sweet spot turned out to be having two pacers, one in front and one behind Kipyegon for the entire race. In that scenario, the reduced air resistance would allow Kipyegon to run 3:59.37.
"If you have just one running in front, you get about a 70% drafting effect," says Kram. "But if you have one in front and one behind, you get about 75% … the runner behind is pushing air molecules essentially against the back of the runner in front of them."
When Kram saw 3:59.37 pop up for this scenario, he was surprised. "That's exactly the same time Roger Bannister ran."
Putting theory into practice could be a challenge
In official track races with pacers, they set off with the other runners from the starting line, but usually drop out before the race is finished. If Kipyegon wanted pacers for her whole race, she'd have two options: use male pacers who could run all four laps, or rotate out female pacers midway through the race, since very few women can run half a mile in two minutes.
Both those scenarios would disqualify the time from becoming an official record, based on World Athletics rules.
"It's always going to have an asterisk next to it because it's not a sanctioned race, it's a little bit artificial," says James Smoliga, a physiologist at Tufts University who wasn't involved in the study.
"Overall, it's a really well done thought experiment … but it is the very best case scenario," he cautions. "These studies are based on assumptions, on top of assumptions, on top of assumptions," he says. Many of those assumptions stem from studies of male, not female, athletes, adding extra uncertainty.
Still, there could be other benefits to pacing that can't quite be quantified.
"It's also psychological," says Kipp, who ran the 3000 meter steeplechase at the 2012 Olympics. "You don't have to really think about the pace that you're running. You're just sitting on this person and they're pulling you through."
Kipp, Kram and Smoliga would all love to see this thought experiment put to the test on an actual track.
"It would be a huge step forward in what's physiologically possible for females," says Kipp. "I think it would also drive a lot of interest in studying the upper limits of human physiology in a female model."
The researchers sent their paper to Kipyegon, who hasn't committed to an attempt, but hasn't explicitly ruled it out either. In a statement to NPR, she said "I appreciate people taking my world record performance as an inspiration to imagine what could be possible in the future. I am concentrating on training in Kenya at the moment with my team and making sure I am prepared to give my absolute best this season."
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