Treadmill vs Outdoor Running
I know this topic has been covered here already but I would like to just try to settle a few things about the differences between running on a treadmill and running outdoors but giving. Im a PhD student in a Physics lab and while I don't really work with gravity and motion etc I do have a good idea of the concepts. Anyway, I was wondering about this myself so I have been doing a bit of research online and have been a bit disappointed / surprised to find so many people with the "intuitive" belief that a treadmill is doing all the work (or some of the work) for you. This simply is not true.
The reason this seems intuitive is because most people automatically think that maintaining a forward motion through space requires a maintained input of power, i.e., if i move something forward at 5mph in a vacuum (no air resistance) and then let go it will slow down unless I keep adding power. They therefore assume that if you are stationary (like on a treadmill) and the ground is moving beneath your feet then because you are not moving forward, there is less power input needed. This is also completely false and I will explain why.
Firstly the simple fact that satellites exist, that the moon remains in orbit around the Earth is proof that objects can maintain a constant speed without power input. Its called the conservation of motion and is a fundamental law of Physics (as explained by Newton). When you are running outside, the Kinetic energy from your forward motion means that if it were not for a few opposing forces such as wind resistance and the friction in your joints, you would never actually stop. So for all intents and purposes, once you stop accelerating and maintain a speed you are virtually standing still. But wind resistance is not the only force slowing you down, or causing you to exert energy. In fact wind resistance at 10mph is actually a tiny force and barely enough to slow you down at all. The biggest opposing force is the up and down motion of your stride and the friction of your joints. When you put your foot out in front of you you slam your foot on the floor and your body moved upwards, this is acting like a break on your whole body. The reason you move upwards is because you have just converted some of your forward motion in to upward motion as basically wasted it. The next thing that happens is that the upward motion (working against gravity) is now paid back to you in the form of a downward motion, which actually does nothing at all to help you move forwards.
Most of the energy you spend while running is spent bobbing up and down trying to give your very inefficiently designed legs room to move for the next stride.
Now that we know we can ignore the effects of moving forward through space, all other opposing forces apart from wind resistance are exactly the same on a treadmill. For example, as the belt is moving towards you it is trying to push you off the back of the treadmill, if there were no friction between you and the treadmill, e.g., if you had a perfectly frictionless wheel beneath you then you would not move, the wheel would just spin beneath you. However we know that this is impossible, there is a great deal of friction between you and the belt as you are constantly smacking your feet down and the force is travelling up through your body and as a result the belt is actually pushing you constantly backwards with quite some force. Also as we have discussed you are also having to bob up and down exactly the same as you would in outdoor running. So you need to balance this force out just as you do outdoors by pushing forward with your legs. This is also the reason why taking large strides is not a good idea. The further in front your foot lands the lower you have to dip to make the stretch, then the more you have to use some of your forward motion to counteract gravity, meaning you bob up and down much more and waste more energy. There is a trade off between taking short steps to minimise bounce and taking fewer steps to minimise energy wastage from constantly moving your legs back and forth (each time your legs change direction and move forward for the next step you use quite a lot of energy).
In short, unless your goal is to fly off the back of the treadmill, the treadmill is not doing ANY work for you. It is actively working against you staying in the same place in space and it requires a lot of work to counteract this force. Because of the laws of motion, it doesnt matter whether it is you that is moving or the ground that is moving. The two are exactly equal. The only additional force outdoors (assuming that you are running outdoors on a perfectly flat surface) is air resistance. In fact as treadmills are often cushioned, you may even be doing a little more work on the up and down motion depending on the model/quality of treadmill. Also you are not being cooled by the wind quite as much meaning your body is overheating on a treadmill.
A good demonstration of how much our stride prevents efficient movement is to get on a bike. The only reason a bike can move so much faster than a human running is because you have eliminated all up and down motion and reduced friction. If you were to ride a bike with egg shaped wheels you would realise just how much energy is absorbed by gravity.
As for the effect of wind resistance, it is difficult for me to demonstrate how small this force is without going to considerable effort (I confess i would have to look up the actual calculations) and it depends on what you are wearing, wind speed, blah blah. I will have to test it more thoroughly myself but if everyone agrees that 1% incline compensates for wind then its probably a good number although a true compensation would be to have a large fan blow a wind towards you on the running machine that matches your running speed. It would also help cool you down
Finally I have not talked about different terrains etc. Obviously these have an effect, as does the incline. Here though I am keeping it scientific and assuming a perfectly flat hard surface with no wind.
Anyway, this isn't a totally scientific explanation, but it doesn't really require one. Hopefully it is now obvious why it doesn't matter where you run and that a treadmill is not working "for" you at all. If you could simulate wind speed then there are no other factors that should make a difference compared to running on a flat hard surface outdoors.
That's one heck of a first post!
Nice write up though, and so true. Put simply, if you're not propelling yourself forwards on a treadmill, you fly off the back! If you truly were only raising and lowering your legs, your feet would quickly exit the treadmill belt.
slightly off topic, but what is better:
walking on a treadmill at a speend of 7.2km/hr or running on a tradmill at a speed of 8km/hr
reason I ask, is that I find I sweat much more when walking fast on the treadmill than jogging at 8km/hr on the treadmill
I'm no expert on actual fitness but I just thought id point out the Physics involved in using a treadmill. I would make one suggestion though.
Originally Posted by *Dim*
Did you know that the human leg has developed to act as a spring? There was a study done a while ago (cant remember who) but they looked at the tendons attached to the foot and concluded that we were actually made for jogging long distances, not walking. The reason is that when jogging we tighten our tendons/muscles and literally bounce on our legs. Remember I said that you convert some of your forward motion to upward motion (against gravity) and this is then repaid to you by gravity by pulling you back down thus wasting energy? Well, this bouncing motion has developed in order to take advantage of the fact that we are going up and down anyway and might as well use some of that wasted energy - thus recycling some of it. This also allows you to take huge steps (compared to walking), move your legs forward and backwards less per distance covered, thus reducing energy usage further. In contrast when walking fast you do not bounce at all so your muscles are absorbing the impact, rather than recycling it. So for going slow it is easier to walk because you can easily maintain a level posture (no bouncing), you don't need to take large strides so you don't need to dip down quite as much. For going fast you need to use the bounce method of running because it is much more efficient as higher speeds. And then there is that region in the middle of 6-8 mph which you can feasibly walk but actually it is easier to run in terms of energy spent because if you try to walk you actually begin to work against the kinetic energy that is building up in your leg. i.e. the faster you move your leg backwards the harder it is to stop your leg and get it to go forwards again, and the faster you go the energy required increases exponentially. You can think of a car engine as abiding to the same laws. If you remain in first gear, its not the friction on the wheels that slows you down, its actually the friction on the engine. The very thing that is pushing you along begins to slow you down because it has its own set of forces acting against it. So think of walking fast as trying to drive on the motorway in first gear its a very fuel inefficient way to move.
So thats probably why you sweat more because you are actually using more energy, which creates more heat through calorie burn and friction.
Again i'm not a fitness expert but I would imagine - if you want to train your walking muscles (for hiking or something), and burn as many calories as possible over the shortest distance, walk as fast as you can. If you want to train for a run and train your running muscles while burning as little energy as possible (you want to try to go as far as possible) then run. If you want to sweat less, run with a fan in front of you.
Originally Posted by malkore
Updated Physics Approach - It's All About the Direction of Gravity!
I agree the long post is a great start to the discussion but I believe I have come up with a physics theory on why a treadmill is easier. I wouldn't have gotten here without the great post up top.
Originally Posted by dprice80
The big factor when running is GRAVITY. Without gravity you could leap from the Earth and fly around for a while. Gravity pulls you down and crashes you into the Earth creating friction which slows you down. Next you got to thrust yourself out AND up to continue to fight this endless cycle.
Now, here's where the difference in running on Earth and running on a treadmill happens.
When you are on Earth, you are moving forward and gravity is pushing straight down. Relative to a fixed point on Earth, you are moving UP and FORWARD when you push off while gravity is straight DOWN.
When you are on a treadmill, it is different. Relative to a fixed point on a treadmill (like the Earth before), you are still moving UP and FORWARD when you push off BUT gravity is now moving DOWN and FORWARD (relative to that fixed point on the treadmill). In this case, gravity is helping you slightly!!!
I know it sounds crazy but think about it. Let me know your thoughts as I'd love to iron this out more.
Something that would be different from most outdoor running and treadmills would be running cross country on a windy, hilly course. This would require the most work.
i believe that running outdoors is better for you. not based on the impact it has on your joints, etc...but because when you run outside you get the fresh air. it's better for you!
Running on treadmills and outdoors both have pros and cons for me. On a treadmill, I tend to take shorter, quicker strides, and have a slightly different form, so it doesn't exactly train me for performance. There's also discomfort from the higher amount of sweat, due to the fact that I'm indoors. Treadmills also have an incline feature, but it's a hassle to keep raising and lowering it to simulate hills. However, running in front of a window, being able to see my reflection, I've been able to work on keeping myself from bouncing up and down while moving and pushing myself more forward than up.
Outdoors, on the other hand, is nicer in that your body is able to cool down more easily. Also, where I live is a very mountainous area, so there's much more of a workout when I'm running on more hills than flat terrain. It sucks when I have to run on pavement though, as that's when I start to hurt.
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