Yes, you are working harder on a curved treadmill. Scientists proved it

At my gym recently, I discovered two new treadmills that looked like minimalist conveyor belts with railings. These were the curved, self-powered treadmills I had heard about—models include the Woodway Curve Trainer, Trueform Runner, and Technogym SkillMill.

I climbed aboard. Because this type of treadmill uses bodyweight and the friction of your foot to move the belt—rather than a motor—my initial steps were awkward. After a few minutes, I realised that my cadence and how far up the front of the curve I stepped affected how fast I moved. I also learned I could adjust the resistance of the belt using a knob on the front of the machine.

Finally, I got situated, but a few minutes later, I found myself panting and struggling to continue. I wasn’t running anywhere near my usual pace, and yet my heart was pounding. Were curved treadmills supposed to make me work this much harder?

According to a study published in the Journal of Science and Medicine in Sport, the answer is yes.

For this study, researchers from the University of Essex School of Sport, Rehabilitation and Exercise Science recruited 13 male runners, all of whom had 5K PRs of 20 minutes or better. They had the runners complete four treadmill runs over a span of two weeks. The first run was a voluntary run to exhaustion, in order to define baselines for each runner’s maximum heart rate, velocity, and oxygen uptake. This run was done on a standard motorised treadmill set to a 1 percent gradient.

On the second run, the participants familiarised themselves with the curved treadmill by practicing the protocol they would follow on the third and fourth experimental runs: 4 minutes running at 5 different velocities (40, 50, 60, 70, and 80 percent of their personal maximum velocity), with 3 minutes of passive recovery between each interval.

In the final two experimental runs, they completed the intervals they practiced on the second run on a curved treadmill and a standard motorised treadmill, respectively. During the last minute of each interval, the researchers measured the runners’ oxygen uptake, respiratory exchange ratio, cadence, and heart rate, and also asked the runners to rate their perceived effort.

What researchers found was that, similar to manufacturers’ claims, runners really do work about 30 percent harder on the curved, non-motorised treadmills. The runners perceived they were working an average of 27 percent harder when they ran on the curved treadmill, and physiologically, their symptoms matched: They consumed an average of 32 percent more oxygen and had 16 percent higher heart rates, 2.5 percent higher running cadence, and 38 percent worse running economy than when they ran at equivalent speeds on the motorised treadmill.

Despite these intimidating statistics, Patrick Schoenmakers, the study’s first author, pointed out that curved treadmills have unique advantages. “Every step you take affects what the [curved] treadmill does,” he said. This means that instead of making a conscious decision to speed up or slow down and then pressing buttons to generate the speed you think you can do—as you would on a motorised treadmill—the curved treadmill allows runners to self-regulate with every footfall, just as they would outdoors. This is useful for runners who don’t like to think about their pace before or during runs, and also for scientists who want to study how athletes will react naturally to stimuli, like the instruction “run harder.”

Schoenmakers also pointed to curved treadmills as being a useful tool to practice hill running for athletes living in flat territory, noting that the machines are a great workout for the posterior chain muscles: glutes, hamstrings, calves. (He and his coauthor, Kate Reed, are working on a study showing curved treadmills represent the equivalent of an 8 percent grade on motorised treadmills.)

Apart from working on those hill muscles, Schoenmakers says he considers motorised treadmill, curved treadmill, and outdoor running interchangeable, so people should use whatever they prefer. The main thing to note concerning curved treadmills is that even once people get comfortable operating them, they should keep in mind at least a 20 percent difference in pace. “Runners can be advised to lower their speeds, so for instance, if they usually run 4:00 minute per kilometer reps (15 kilometers per hour, or 6:43 minutes per mile) in their training, a speed of 12 kilometers per hour (8:03 per mile) will mimic that,” he wrote in an email. “The same conversion factor can be used for long distance and tempo runs.”

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