Pedal physiology
May 11, 2021 10:27 AM   Subscribe

Why do I sweat (but not get short of breath) on the stationary bike and get short of breath (but not sweaty) on the 'real' bike?

I started taking spin classes recently and I get totally drenched in sweat during these. We're actually outdoors because of COVID but I'm still pretty saturated by the end. I never get short of breath or have trouble catching my breath no matter how hard I'm riding though.

Meanwhile, when I ride to work I get winded on hills. I'm mildly asthmatic and exercise is a trigger. I'm not very sporty and tend to huff and puff a lot when I have to really push, to the point that I sometimes have to dismount because I actually cant breathe.

Why would the impact of such similar exercises have these different physiological responses??
posted by latkes to Sports, Hobbies, & Recreation (12 answers total) 1 user marked this as a favorite
Not sure about the shortness of breath (maybe even the highest resistance level you use on the stationary bike is less than the force required to bike up a hill?) but I imagine the lack of sweat on a real bike is because you’re moving through the air so you have a constant breeze to cool you.
posted by mekily at 10:31 AM on May 11, 2021 [10 favorites]

Just a guess: if you're moving, the air you are moving past evaporates your sweat faster than the air moving much more slowly past you on a spin class bike.
posted by gauche at 10:32 AM on May 11, 2021 [8 favorites]

The wind is drying to your mouth/lips which will have an impact on your bronchial tubes/lungs. Also, because the wind will better lower your body temperature/strip the sweat from your body; you might be working harder than you are in spin classes, despite the sweat making you think otherwise.

Going up the hills, if you're not efficiently working your gears, you might be getting a completely different workout than you are on the spin bike. You should gear up/down so that you're managing about 90 full RPM's of your pedals. I.E. within a minute your left foot should be at the bottom 90 times or more.
posted by nobeagle at 10:33 AM on May 11, 2021 [5 favorites]

Not abusing the edit window; on a real bike, you'll be using your core muscles more to help balance while pedalling. On a stationary spin bike less so. The different core workout will effect your breathing.
posted by nobeagle at 10:35 AM on May 11, 2021 [2 favorites]

What I notice is that on the spin bike, I get drenched in sweat when pursuing high RPMs, but if I'm up out of the saddle and using more resistance, I don't get as sweaty (and I think this negates, at least in my experience, the idea that it has to do with core muscles, because I use those like crazy out of the saddle). When I'm on a real bike, my RPMs are never as high as on the spin bike and often the resistance is higher. I think it's just two different kinds of effort (plus the evaporative effect of moving through space).
posted by HotToddy at 10:44 AM on May 11, 2021

I ride a stationary bike (on my back porch, so also outdoors) and a road bike, a lot. The effect of air moving over you has a huge effect on cooling (so you sweat less) and sweat evaporation (so the sweat you do produce goes away). I use a fan for stationary rides when it's above ~70°F.

I can't speak to the effects of being asthmatic, but I can say that sudden increases in load will force your heart rate to go up because you need to supply more oxygen to your body, in order to convert glycogen to glucose: even once you're well warmed up, it can take over a minute for your heart rate to reach it's "target" for your current load, and until then, you're relying on the small amount of readily available glucose in your system to make up for the deficit of oxygen; you also wind up panting because you need that oxygen. If you found yourself on a long, steady hill, you might find that breathing actually got a little easier once your heart rate stabilized (barring asthma attacks).

You could probably simulate the effects of a hill on your spin bike, and push yourself into shortness of breath pretty easily. It would be interesting, if nothing else, to get a heart-rate monitor to see if there's a certain heart rate (or change in heart rate over time) where shortness of breath is triggered.
posted by adamrice at 11:06 AM on May 11, 2021

On top of what everyone's said, another thing that might be contributing is that you're probably predominantly staying in the cardio / aerobic thereshold during your spin class. Spin classes typically only venture into anaerobic threshold (intense short sprints or heavy resistance) for less than a minute at a time, and so that you're probably able to keep good control of breathing.

Outside, and especially on hills, it's fairly easy to get into prolonged anaerobic threshold efforts, requiring much more sustained power output resulting in heavy breathing.

I experience the same phenomenon now that I think about it (except I def get sweaty outside too lol), thanks for the fun thought exercise!
posted by blueberrypuffin at 11:08 AM on May 11, 2021 [1 favorite]

I'd echo a lot of the above and add that when I'm on a stationary bike, I never coast. It's constant pedaling. Yet when I'm on a "real" ride outside, even a strenuous one, there are frequent stretches where I'm not pedaling at all and just coasting along.
posted by cyclopticgaze at 11:19 AM on May 11, 2021 [2 favorites]

The wind is drying to your mouth/lips which will have an impact on your bronchial tubes/lungs.

Do you wear a mask while biking? If not, there is a real easy way to see if this is a factor.
posted by aniola at 11:56 AM on May 11, 2021

Could the shortness of breath while commuting also have to do with air pollution, if you are riding on roads near cars?

Agree that the sweat difference is almost certainly due to evaporation.
posted by Ausamor at 12:12 PM on May 11, 2021

Lack of wind and lack of gravity.
posted by rhizome at 12:53 PM on May 11, 2021

The thing I noticed immediately when I started to bicycle outdoors was that the workout was actually much more intense while not feeling nearly as difficult. Riding up just about any local hill was an "interval" more intense than any I was able to push myself to do inside.

Inside, I would push myself as hard as I thought I could. Outside, there is that hill and you just have to get to the top of it, and so you just make it happen.

(By the way, this isn't just hearsay--when I finally got heart rate monitors etc etc all those bore out in the numbers.)

This, to me, explains the out-of-breath-ness outdoors but not in the gym. You're just pushing yourself a fair bit harder without quite realizing it.

Here is a mildly funny story that might illustrate:

I've been bicycling quite a bit outdoors all through this winter, but a lot of it is pretty flat and due to Covid mopiness I've almost always been training at a pretty low level of effort and a very moderate heart rate--maybe 70-75% of max.

So then I've noticed, even when I climb a hill or whatever, my heart rate just stays there. It doesn't climb up to 80% or 85% or 90% even when I "think" I'm putting in a pretty good effort climbing a hill or whatever.

"Maybe I just can't get it up that high any more," think I.

Then today I'm out riding and I see these two roadies approaching--slowly--in my rear view mirror.

"I'll just give these two guys a little run for their money before they drop me," think I.

So I move things up a notch and then another notch and then another and another as they gradually drew closer.

When the one guy finally pull up to me I was going a good 5mph faster than I usually "can". When he pulled a little ahead I was able to maintain that for maybe 15 minutes. (The second guy was flailing a long ways behind the two of us and never did catch up.)

I look down, and there we are at 90-95% of max heart rate. (And yea, I was breathing pretty hard whereas 70-70% max heart rate is where you can hold a nice conversation with anybody you happen to riding with. No noticeable out-of-breath-ness at all.)

So . . . that much higher heart rate and much higher wattage output was just the kind of thing I thought I "couldn't" do any more.

It's not that you "can't" but rather that it just requires the right type of motivation. In this case, the motivation was trying to hang on with a rider who was just a little bit faster than I was.

For most of us, real stuff outside--whether it's real hills or a real time trial (formal or informal) or trying to hang on to the back of your riding buddies--is far, far more motivating than anything you can do on an exercise bike or machine.

(Also, as a rule you can't hold that high an intensity level indefinitely. You can hold it for 3 or 5 minutes to climb a hill, or hold an even higher intensity level for 30 seconds while you're sprinting against someone to the city limit sign, or whatever. Part of the trick of outside riding is that you always have these little challenges, whether they are hills or just regaining your speed after each stoplight or stop sign. Outside riding--and exercise in general--is very irregular whereas in a gym or on a machine you're likely to hold a steady amount of effort and/or heart rate target for a long time.)
posted by flug at 11:19 PM on May 11, 2021 [3 favorites]

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