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I have a treadmill, which I use for 20 minutes a time, about 3 or 4 times per week. I usually manage quite well, coming off tired and hot, but not particularly out of breath.

The other day, I realised that I was holding on to the handlebars for stability all the way through, and wondered how I would get on without. To my surprise, I found myself out of breath after only a minute or so, and found it quite a struggle to keep this up until the end of the session. Afterwards, my heart was beating far faster than it ever did when holding on, and it took a while before my breath was back to normal.

Can anyone explain to me why this was so? As I said, I was only using the handlebars for stability, I wasn't putting any weight on them.

Thanks

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The greatest factor is an elaboration to Thomas' answer. It isn't just downward force, it is also forward. You do reduce your weight if you push down on the bars, but more importantly you produce tension in your arms between you and the bars. From a physics perspective, that tension is equivalent to the forward force on your body.

To help visualize it, think of a toy car or wagon tied by rope to the front of the treadmill. It can keep up with the treadmill despite the fact that it cannot even move under its own power. The force to keep up is provided by the tension in the rope. In the case of a human, you need to move your legs to keep yourself suspended but you aren't moving yourself forward, just keeping yourself stable while you are pulled along.

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    Demonstration - after a tiring arms session, especially one with lots of pullups, bench rows etc., go on the treadmill to finish off. You'll feel your arms working to pull you forwards
    – Chris H
    Dec 8, 2022 at 21:31
  • It would be similar to running while holding onto the back of moving car (not recommended). It's liable to help you keep up speed.
    – WaterMolecule
    Dec 9, 2022 at 20:30
  • It would be interesting if the bars were able freely slide forwards and backwards, with a sensor to ensure they are never pulled all the way to the end of their sliding range. Then the user could hold them for stability up/down & sideways but not be pulled forward.
    – bdsl
    Dec 10, 2022 at 23:18
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It makes you "weigh" less.

The answer here is simple physics. When you run on a treadmill, you still have to propel your body weight up and forward relative to the motion of the belt. When you grab the handles, you are reducing the force required to put into the belt by holding yourself up on the handles. Even if it doesn't feel like you are putting that much weight into the handles, you could be putting twenty or thirty pounds into them without really feeling like you're using them to support yourself, and this makes running substantially easier.

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  • Thanks for the answer. I did wonder about this, and tried not actually holding the handlebars, but putting my hands to the side of them, so I had the stability, without putting any weight on them. This still made a lot of difference, which is why I rejected that idea as being the cause. Not saying you're wrong, it just doesn't seem to explain such a big difference
    – Avrohom Yisroel
    Dec 8, 2022 at 16:19
  • @AvrohomYisroel not pressing hard to the side I hope (i.e. not supporting your weight, even the weight of your forearms, by friction)
    – Chris H
    Dec 9, 2022 at 6:45
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    @AvrohomYisroel Stabilizing yourself with your arms is taking away the work your legs would have to do to stabilize you. No matter how you slice it, any support that isn't from your legs is going to reduce how hard your legs work -- and keeping stable is quite a lot of work. Part of the reason running injuries are so common is because it's easier to over-stress and damage the muscles used for keeping stable than it is to harm those doing the "heavy lifting" (so to speak), or to damage tendons, ligaments, and joints when those muscles fail.
    – Matthew Read
    Dec 9, 2022 at 19:11
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In addition to Markov's answer, the bars provide stabilization, requiring less effort to keep yourself aligned properly. It is, in some ways, similar to how someone might be able to lift more weight in a weight machine, which constrains motion to a particular direction, than they could in the corresponding free lift. Because you have to exert more energy to keep yourself stable, it will require more effort, particularly so if the stabilizing muscles are not ones you're used to exercising.

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  • I assumed this, but was surprised that sideways stability took so much effort
    – Avrohom Yisroel
    Dec 8, 2022 at 16:20
  • @AvrohomYisroel I'm not into treadmills these days, but find that stability takes more effort than running outside. That might be because the visual cues don't match the motion. But this is something you can test - see whether you need a grip at the front, or whether light finger contact on the side bars (assuming there are side bars) makes much difference
    – Chris H
    Dec 8, 2022 at 21:29
  • I only need a light touch on the bars to keep me stable. That's why I was surprised that you mentioned stability as the probable reason. Maybe it's just my false perception that stability doesn't need much effort. Maybe it's much more than it seems. Thanks again
    – Avrohom Yisroel
    Dec 8, 2022 at 22:43
  • @ChrisH pretty sure that treadmills require less energy overall because the vast majority of them have a springy running board that returns energy to you. It's harder to judge how much stability effort is required, but the energy consumption can be easily measured by recording your heart rate at a set speed for both. I see a 5-10 bpm difference which favors the treadmill.
    – Lawnmower Man
    Dec 9, 2022 at 0:07
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    @AvrohomYisroel the force needed to keep you stable is minimal. That's why I mentioned finger contact. Very different but I'm learning to ride a unicycle and while catching a fall riding along a support obviously takes a fair bit of arm force, maintaing balance when you're essentially balanced can be done with one finger.
    – Chris H
    Dec 9, 2022 at 6:43

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