In the calm hours before dawn, as I glide along the empty running path with shadows racing past in the dim moonlight, I feel fast. My watch, however, tells a different story. My split times during these races are usually slower than I expected based on my effort. It’s not just that I get up earlier than usual or run on an empty stomach. It turns out that running in the dark is really harder.
At least that’s the message I take from an interesting new study conducted by researchers at the Royal Swedish Institute of Technology KTH, in collaboration with the Swedish military and Slovenian colleagues. They had noticed that soldiers on night marches seemed to burn off more energy than would be expected from the physical demands of the mission, especially when wearing night vision goggles that restricted peripheral vision. They wondered if not seeing caused soldiers to alter their strides, sacrificing efficiency for stability, so they decided to test this theory.
The new study, published in the European Journal of Applied Physiology, asked 15 volunteers to do a series of ten-minute treadmill walks under four conditions: with and without a 56-pound bag, and with and without a blindfold. The treadmill was set at a comfortable pace of about 30 minutes per mile, with a laser warning system to alert them if they were about to fall off the back of the treadmill.
The results showed that oxygen consumption (an indicator of energy consumption), respiration and heart rate increased significantly when carrying the heavy bag, as expected. The surprise was that they increased by roughly the same amount when adding a blindfold. Here are the graphs of these three parameters, with (circles) or without (squares) the band:
If you compare the circles on the left (i.e. blindfolded with no backpack) to the squares on the right (i.e. without blindfolded with a backpack), you see that they are almost identical. In other words, walking with a blindfold on takes as much extra effort as walking with a 56-pound bag. To be specific, the backpack increased oxygen consumption by 20%, while the eye patch increased oxygen consumption by 19%.
The explanation for this effect appears to be that the subjects adjusted their strides while blindfolded: their steps became 11% shorter and 6% wider, and they also lifted their feet 18% higher. Keep in mind it’s on a perfectly flat treadmill, so there are no bumps or potholes to avoid: it’s just an instinctive response. It should also be noted that the effect is probably not just due to them being unfamiliar with the challenge of walking blindfolded: a similar test on blind subjects found that they burned around 25% more energy when walking than sighted witnesses.
Of course, being blindfolded is far more disruptive than wearing nighttime goggles or simply going out at night in low-light conditions. This means that the size of the effect is probably exaggerated. And walking is different from running. But it seems reasonable to assume that similar mechanisms are at work when you’re running in the dark, along with other, more subtle mechanisms like optic flow, which is the pattern of objects passing through your vision as you move in space.
When running or cycling in the dark, you can only see objects that are relatively close to you. This means that they only appear briefly in your field of vision before disappearing behind you, which corresponds to faster optical flow than you would have in daylight. A few previous studies, notably those by Dave Parry and Dominic Micklewright of the University of Essex, have attempted to manipulate optical flow in virtual reality setups, making the landscape pass faster or slower than treadmill speed or of the exercise bike. Sure enough, when the optical flow is faster, like you would in dark conditions, you feel like you’re moving faster, and any given pace feels harder.
There is an interesting corollary to these optical flow discoveries, as Parry explained to runner’s world Scott Douglas in 2012. “Running in an environment where most of the visual reference points you can see are close, you feel a greater sense of speed than in an environment where your reference points are far apart,” said Scott Douglas. -he declares. This means that running in a forest or on the streets of a city will probably be faster than running in an open field.
Since reading those optic flow results, I’ve dismissed the discrepancy between my actual and perceived pace during night runs as an oddity in how my brain estimates effort. For most of my runs, that gap doesn’t matter, but if I’m trying to do a tempo run or heavy training before sunrise, the slower pace can be a bummer. So I’ll take the new Swedish results to reassure me that running at night really might be physiologically harder, not just a brain error – and if that’s what it takes to avoid tripping in the dark, I I will accept the compromise.
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