It’s breathtaking to watch the fastest, most athletic people on Earth compete for world records, but we might not look quite so good if we let other animals play — especially when it comes to jumping, swimming and running. This week Scienceline talked to experts on human running to find out how we stack up at top speeds, what slows us down, and whether we’re going to get any faster.
How Humans Rank (and Who’s to Blame)
Peak human running speed, compared to other similarly sized land animals, is “absolutely rotten,” says animal locomotion expert McNeill Alexander of University of Leeds in the U.K. If Usain Bolt, the current world record holder in the 100-meter dash, raced the 50 fastest animals, he would come in around number 28, just ahead of the elephant. (The cheetah, of course, would take the gold, and the prong-horned antelope the silver.)
Our main disadvantage, Alexander says, is the considerable heft of our limbs. “We’re still suffering from having evolved from apes,” whose tree-swinging lifestyles require “big grasping feet and plenty of muscle all the way up the leg.”
What would make humans faster, says Alexander, is if we had legs more like an ostrich. Ostriches run around on their toes, with their ankles “a good bit of the way up the leg,” and carry almost all of their leg muscle on short thighbones at the very top. They can run up to 43 mph, compared to Bolt’s nearly 28 mph.
Our feet are also a setback. Unlike ostriches, which have smallish feet but manage to keep their balance by spreading their wings as they run, humans have evolved big, floppy feet to keep them upright. What we gain in power and balance from these oversized appendages is more than lost in the added weight and awkwardness they bestow.
Our Species’ (Theoretical) Personal Best
Given our ponderous limbs and feet, it’s a little surprising that humans (read: Olympians) have achieved the speeds we have. And we keep getting faster — in 1936, Jesse Owens reached a speed of 21.7 mph while breaking the world record in the 100-meter dash; in 2009, Usain Bolt reached nearly 28 mph.
But how much faster can we get? Is there a biological speed limit to human running?
Peter Weyand, a researcher who studies human running at Southern Methodist University in Texas, says there is: humans should theoretically be able to run up to 35 or 40 mph. Weyand published this estimate in January in the Journal of Applied Physiology.
For a long time, running experts assumed that the ultimate limit to how fast we can run was set by the maximum force our feet can generate against the ground. In order to find a biological limit to running speed, Weyand and his team first had to test this theory. They measured the force elite runners generate against the ground while running versus hopping on one foot, and found that hopping generated 30 percent more force than running. In other words, runners sprinting at top speeds don’t use the maximum force possible with each stride.
Then, Weyand had his subjects run forward and backward and measured the foot-ground contact times. Surprisingly, the amount of time the runners’ feet spent on the ground in each case was almost exactly the same, suggesting that there exists a lower limit to foot-ground contact time.
Taken together, these findings suggest that runners could generate more force with each step, but getting those peak forces requires the foot to spend more time on the ground. “It’s impossible to run faster and faster and faster without reducing the amount of time that your foot is on the ground,” says Weyand. So the limit to human speed must be imposed by this foot-ground contact time, rather than the force our foot uses against the ground.
Using this minimum contact time as a limiting factor, Weyand determined that humans should be biologically capable of running 35 to 40 mph.
How Fast Are Your Fibers?
If human speed is largely a matter of how fast our muscles can activate and pull on our tendons, to pull on our bones, to push off the ground, our limits can be traced to the molecular level — what Weyand calls our “internal gearing.”
Humans have three different types of muscle fiber, two fast-twitch types and one slow-twitch. Fast-twitch muscles, like the ones that control our eyeballs, fire quickly and are good for expending speedy, short bursts of energy. Slow-twitch muscles, like the ones that help us stand around for long periods of time, fire slowly but can work over long periods of time. The proportion of fast-to-slow twitch muscle fibers in our legs varies from one person to the next.
But not all fast-twitch muscles are created equal. For example, says Weyand, the fast twitch muscles in a hummingbird, which beats its wings 50 times a second, “are orders of magnitude faster than the fast-twitch muscles in an elephant.”
Unfortunately, Weyand says, “there’s a downside to having muscle fibers that contract really quickly — they use a lot more energy.” Big animals like humans wouldn’t be able consume enough energy to keep a large proportion of fast-twitch muscles up and running.
“So what nature has done with these very fast animals, is they’ve ignored the option of gearing up the muscle speeds,” explains Weyand. Instead, they have adapted ways of taking longer strides, making foot-ground contact time less critical. This explains adaptations like the elongated legs of an ostrich or the flexible backbone of a cheetah, which “bends like crazy” to get the maximum possible distance out of each stride.
Unlimiting Our Limits
Without the necessary pressures, humans aren’t likely to pick up any adaptive tricks for speed, and Weyand’s estimate for our biological limit doesn’t tell us anything about our own personal top speeds.
So how can you, as an individual, become a faster runner?
The short answer, according to Weyand, is “you can’t.” Because our genes determine the proportion of slow and fast muscle fibers we carry, we are — in a sense — born with our top speed already determined. Elite sprinters tend to have a higher proportion of fast-twitch muscle fibers, while endurance runners tend to have a higher proportion of slow-twitch.
Bob Fitts, an exercise physiologist at Marquette University in Wisconsin, agrees. Training can help with endurance, he says, and with neural adaptations — meaning that the nerves can be trained to activate the muscles faster. And of course, strength training can give you bigger muscles and more power. But, Fitts says “you’re not going to switch fibers to fast fibers, other than a few percent … unless you go to space.”
The genes in our muscle cells that code for twitch speed, Fitts explains, are regulated by two things — how much the muscle is activated, and how much load it’s carrying. When weight is “unloaded” from astronauts in space, the structure and function of the muscles begins to change. Unloading causes the genes that make fast-type muscle tissue to turn on, and “with no gravity, your slow muscles become about 30 percent fast,” says Fitts.
Who Wants a Hummingbird Hamstring?
The idea that we can’t do much — short of going to space — about the speed of our muscle fibers isn’t likely to satisfy people forever. If muscle fiber type is determined by our genes, couldn’t we just splice some of those fast-twitch hummingbird genes into our own DNA? Wouldn’t that make us run faster?
“Radically faster,” Weyand says. “If somebody manages the technical trick of having really fast animal fibers introduced and expressed, then all bets are off. Really crazy things would happen.” Another possibility, he says, is that our own existing DNA could be manipulated to code for the fast-type muscle fibers. “You’d see some crazy stuff then, too.”
Weyand points out that the science is already in place to make this happen. In fact, researchers at the Salk Institute in Southern California accomplished this feat with lab mice in 2004, causing a switch from fast-twitch to slow-twitch muscles that helped the mice burn fat. Similar studies in the years since have repeated those results.
“That’s the whole gene-doping scenario,” says Weyand, “that’s probably … not very far away.”
Exactly how far away is gene-doping? Some people are watching the Winter Olympics in Vancouver this week pretty closely, trying to find out.