A treadmill isn't real running, right?

I've always wondered about something that I find a bit subtle. Suppose a cart is rolling and as it rolls, a heavy object drops straight down into the cart. What happens? The cart continues moving, but at a lower speed. The best way to understand this is conservation of momentum. The cart gives some of its horizontal momentum to the object, so the final velocity is between the two initial velocities.

Now, the situation is much more complicated in the treadmill situation. For one thing, the treadmill belt is being moved by a motor, and for another, the runner's foot moves past their center of mass as they run, so the belt and the runner aren't really "coupled" like in the cart example. I believe the momentum of the belt could be roughly replaced with its "inertia" (how hard it would be to stretch and/or hold in place). For the second complication, I think a runner's center of mass does move backwards while they are on the belt.

If these assumptions hold, the result would be that the belt slows down when the runner is on the ground. Then it speeds up when the runner is in the air, and so on. It's a very minor version of hanging on to the armrests, and the result would be that the treadmill would think the runner is running faster than they actually are.

Any physicists or engineers here have an opinion on this? There's got to be some belt slowdown when the runner is on the belt. Is it enough to make a significant difference in recorded speed?

I find treadmill running harder than running outside …. My pace is almost 30-45 seconds slower on the treadmill and same heart rate… I wouldn’t even go so far to say same effort, as I find my effort on the treadmill is much harder than outside due to heat( and I do have a fan on the treadmill and a fan in my back to help). For me, 7 minute mile pace outside is almost equivalent to 7:45 on the treadmill. Different strokes different folks I guess…I just wish I had handles to hold onto or sides to step on while Im outside…. I find the treadmill is a great way to recovery run, not worry about pace, take a break off the pavement and just let my heart rate dictate how I’m feeling on a recover day…. Actually impressed to read about some people that trained on treadmills almost exclusively and went in to win USA…. After lockdown, and running exclusively on the treadmill I got so dizzy my first few runs I had to stop as it was like traveling in a car for the first time…. Too much crap moving in my peripheral vision it made me sick.

Can confirm that running on a treadmill is easier. Just did a tempo outdoors today after doing my last several on treadmills, and the effort required outdoors to hit the pace I was doing on the treadmill is much higher. Definitely some combo of wind, terrain, and not being able to "hold on" to a set pace (plus other things).

Michigan had a test on this and I’m sure there have been others, but environment is a huge factor. If you run in silence on a treadmill, staring at a wall in a dry/heated room, the mental and cardiovascular effects are worse on a treadmill and can slow you down

study referenced in this article:

compedgept.com

Running Outside vs. Running on a Treadmill: Which One Is Better for You? - Competitive Edge

Alyssa Razmus

A treadmill can be your best friend for training in icy conditions or getting in early morning runs when dark conditions make outdoor running dangerous. Treadmills are great for pre-programmed speed workouts to keep you from...

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I think the treadmill is the next best thing to running outside for training purposes so in this way it’s very much real running. However, I personally would never consider a treadmill time to be a PB as I consider them to be different exercises. If your acquaintances are boasting about their treadmill times as if they are as valuable as race times then they’re wrong in my opinion. However, strava showing them as people’s running PBs just sounds like a problem with strava. And the fact that you are able to see that these were treadmill workouts allows you to use your own judgment on their value as can everyone else.

Both on and off a treadmill, a good footstrike hits at rest relative to the surface. It and the treadmill exert no lateral force on each other.

As for center of mass, the lead leg forward of the body compensates for the trailing leg moving behind it.

If you think about this for a while, it may revolutionize your grasp of running form. Most people think they're pushing the ground backward, focused on their trailing leg. It's closer to just moving your arms and legs back and forth while alternately hopping on one foot, maintaining your inertial velocity. Just like on a treadmill.

From what I've observed most treadmill devotees will "hop" from one foot to the other in an attempt to approximate a running motion.

It's been awhile since I've done any Physics mechanics (so I could be wrong), but re: Belt slowdown from significant foot impact: Yes and No. Mainly No.

It does depend on the Runner's form, what shoes they are wearin,g and how good the treadmill is (in terms of motor power and belt quality/flex and other design features).

I'd say all else being equal, what you are describing is very, very marginal when it comes to influencing performance/speed on the Treadmill compared to outside. I mean sure, there is slightly less push off force required (and your form does change slightly usually) because of the nature of the moving belt...but of course other things like treadmill calibration, how level the floor surface it is on is etc probably play a much bigger role.

Of course the biggest thing that makes treadmill running "easier" than outside is the lack of air resistance. This is especially noticed at over 10-11mph. Run a 5:00/mile on the treadmill and it's more like a 5:12-5:14 for most people outside in terms of energy cost. Gotta keep the temperature cool though!

I’m going to find out soon.

I’ve been doing 10x1 mile since December all on the treadmill. 2-3 times per week. Taking 2 minute rests between mile repeats. My pace has been intentionally about 10-15 seconds per mile slower than my marathon goal pace 95%. I’m just trying to build some modest fitness. The session takes 75-80 minutes to complete. I’ve been meaning to get outside and compare effort and Heart-rate but have been to lazy to run in the cold. I’ve done this session about 15 times and literally zero other actual running or jogging…just cross training outside.
I’m curious about 2 things. Does doing 10x1 Mile at marathon effort 2-3 times per week translate to a decent marathon & does doing 100% of my training at marathon effort for 2-3 months indoor translate to outside running.
I’m hoping to start running outside next week. I’ll have 6 weeks to adjust for an April marathon.

The belt slowes down (a little) during touchdown, to accelerate again to hit the target pace.

The reverse happens if the runner is in the air. The belt is faster for a short period (less resistance), and will be slowed down by the electronics to hit the target pace.

At the end of the day, you get some kind of sinus curve for the velocity over time.

Does anyone else find that it feels like it takes more effort to run on the treadmill versus outdoors?

For example, 8:30/mile pace feels like sub-7. The heart rate monitor shows 140 bpm after 20 min. at 8:30 pace. Maybe it's the lower quality treadmill at Planet Fitness that is a significant factor?

One of the engineering issues with treadmills is that the moving belt is sliding over the fixed deck. On foot impact the friction between belt and deck increases which wants to slow down the moving bits, belt/rollers/motor/flywheel or make the belt slip on the rollers. The degree to which this happens depends upon the quality of the treadmill such that more powerful motors and more massive drive trains show little noticeable effect.

Poorly built "walking grade" treadmills that do this more will noticeably affect one's stride. I once tried to use a hotel treadmill that was so bad in this regard that I quit the session for fear of injury. It can be very disorienting.

Of course, it is different!

I set my machine to 1.5 incline which seems to be about equal to outdoors in terms of effort. But it is still different because there are no turns, changes in surface, weather or pacing to contend with. There are some disadvantages as well like not having a running partner to feed off of and boredom. With all of that said, the treadmill is excellent for training and does not have to be used just when it's raining. Back when I was in a serious training group, 2 of our world class athletes would jump on a treadmill from time to time.

Those considerations are interesting. But let's envision, hypothetically, a "perfect treadmill" Because I think a lot of people think running on a treadmill is inherently different to running on the ground, their reasoning being that a treadmill is moving and the ground is not. They think the belt of the treadmill is pulling their foot backwards during the time it is planted on the belt, which makes it different to "normal" running.

But that's not true, at least not when the treadmill is moving at a constant speed. To those people, I suggest picturing yourself in a gym with no windows. You run around in the gym and everything seems normal. Then you open the gym door and look outside, and realize that the gym is actually sitting on an enormous conveyor belt moving at a steady 10mph. This means you are essentially running on a treadmill. You go back in to the gym to double-check. You jump straight up in the air. Does the gym floor slide several feet under your feet while you are in the air? No, you land in the same spot. That's just physics.

Or think of standing on a bullet train going a steady 200mph. That is essentially the same thing as a treadmill belt going 200mph. Nothing weird would happen when you tried running up and down the hallways of the train.

I agree with S Canaday - the only difference running on a (good) treadmill is the lack of wind due to being stationary relative to the air.

I didn't say it was the "only difference"....just the Main Difference. Given the "imperfect" (aka "more real") Physics model as we discussed above with a few posters who seem to understand some basic Physics there is certainly some belt "slippage" and deceleration/acceleration and a change in running form (however slight). All that seems very, very marginal though relative to the lack air resistance.

But in regards to air resistance and speed imagine the difference of running outside directly into a 10-12mph headwind (vs on a still day). That is the kind of difference you're getting when you take away air resistance inside on a treadmill at 6:00min/mile to 5:00min/mile paces. Generally if the incline is set to about 1.5% at those speeds (give or take) you're looking at a more "equal" work output to outside running at that same speed as the extra climbing negates the benefit of lack of air resistance. I think a lot of treadmills probably aren't calibrated well, they aren't leveled perfectly, it tends to get really hot and stuffy on a treadmill (unless you're in a cool room with a fan) and mentally it's super boring....so a lot of "subjective things" make people think treadmill running might be "slower" or "feel harder". But basic Physics says otherwise.

With planetary-surface running, the planet is spinning. All you really need to do is lift your feet up and down, and you're moving quite fast regardless. It's not real running.

Be careful if most of your season is on a treadmill that reduces impact, if you change back over to roads, it's easy to tear a calf or bomb your quads.

I also feel like treadmill running is much harder than running outside. Overheating and my individual running mechanics slow me way down on the treadmill. I normally avoid running on the treadmill but ran a few times on the planet fitness treadmills when the roads were too slippery to run on. I also found myself feeling like I was really moving running at 8 minutes/mile on the treadmill. In comparison, 8 minute miles feel quite slow outside unless I am going against a fast headwind or uphill. My heart rate was also way higher than when I run at that pace on the roads on a cool day. So much for increasing the incline, the treadmill already is lot harder for some people at 0%!

Out of curiosity, do you know what brand of treadmill did you ran at Planet Fitness? I ran on a Precor. Also, did you know what temperature it was when you were running? The thermostat was set to 72°F at the Planet Fitness I ran at. Way to hot for me, but l have been to other Planet Fitness locations before that had the temperature at 80°F.

I recall the brand name of treadmill is Matrix, I believe. I'll have to find the thermostat next time I'm there.

Also, I didn't consider that my mechanics may not be doing me any favors on the treadmill. I imagine setting it anywhere near 7:00/mile pace would feel like a very strong effort. Running outside at 7:00 wouldn't be an issue.

For context - I'm 34, athletic and my most recent 5k time is 19:XX a few months ago.