Saturday, September 29, 2012

The Physics Of Fittness - Getting It Not Quite Right

I'm always happy to see when physics is explicitly mentioned as being involved in many of our daily routine. Many of us know this in the back of our heads, but it is always educational when it is mentioned explicitly, especially to laymen, so that they are aware that physics isn't just something one deals in school.

Unfortunately, while the intention is good, the application of various physics principles can often be rather dubious, or filled with errors and misunderstanding. I have been known to nitpick (I fully admit that) stuff like this, not because I like to nitpick, but I think things can be done a lot better and clearer without having to resort to such errors.

This article is one prime example, where they could have gotten it right rather easily, but didn't. I suspect that there is a bit of unclear understanding of simple basic physics here, The writer is trying to point out how the 3 Newton Laws are at work in a fitness routine. Let's go over some of the puzzling aspect of this article.

The first law of motion dictates that an object at rest will stay at rest, and an object in motion will stay in motion. I use this for mental motivation and often say, a person on the couch tends to sit on the couch… but a person who gets up and moves around will keep moving around. An exercise example is the bicep curl. Until your biceps contract to pick up the weight it’s at rest, and gravity constantly tries to pull it back to  rest on the ground.
Right off the bat, the first law is stated in a rather incomplete form. The object will stay at rest, or will remain in motion unless there is a net force acting on that object. This is rather important omission. Furthermore, the object in motion will stay in motion with a constant velocity. The example given in this paragraph of " .... a person who gets up and moves around will keep moving around... " isn't quite accurate because we don't just move in a straight line with constant speed! Not only that, the example given with the bicep curl is a bit confusing. If you stop moving somewhere in the middle of your bicep curl and remain still, you are not doing any work mechanically, but your muscles are certainly doing work and burning calories to maintain that position. The "rest" position isn't just the weight resting on the ground!

Newton's second law of motion states that force equals mass times acceleration. A good example of this when exercising is illustrated when you perform a bench press. The amount of weight you can lift is directly related to the amount of force exerted on the weights by your muscles. Increasing the weight requires more force to lift it. Also, doing reps faster (increasing acceleration) requires more force to be exerted.
This is confusing because of the way it is stated. "The amount of weight you can lift is directly related to the amount of force exerted on the weights by your muscles." What should have been stated here is that the minimum amount of force one must exert to lift the weight must be equal to the weight itself (here, I'm using the term "weight" to mean W = mg, so this is where Newton's 2nd law comes in). The way the statement is stated, it is more related to the 3rd law, which comes next. The last part of the paragraph also has more relevance to the 2nd law than what was stated in the beginning of the paragraph. However, does lifting the weight faster a better way to build muscles? I've read many fitness instructions that insisted that one lift weights slowly and deliberately to really "push" the muscles involved.

When your foot hits the road (or treadmill) you apply a force to the ground, which responds with an equal and opposite force, helping to propel you forward. As you speed up, either the length of your stride or how frequently your foot hits the ground increases. Working to improve your running stride can help make every run feel less taxing, increasing both the speed and distance you can cover.
Again, this illustration of Newton's 3rd law is confusing. What propels you forward is friction, not the equal and opposite force that is the result of the force you apply to the ground. The equal and opposite force here means that you don't crash through the road or your treadmill. Rather, this is where the weight lifting example in the previous paragraph would have been more relevant.

The writer than has more confusing article on other issues of biomechanics.

The biomechanics of stability, the less an object’s surface area touches a solid base, the less stable that object is. Applying this basic principle into exercises makes our whole body work harder, meaning a higher calorie burn, plus a more challenged core.

Try This: Make any strength move more challenging by narrowing your base (bringing your hands closer together during pushups or feet closer together during squats), removing a point of support (doing single-leg dead lifts or planks with arm raises), or replacing your sturdy surface with a wobbly one (placing your hands on a stability ball during planks and pushups, or stepping onto a BOSU trainer during lunges).
Now, by bringing your hands closer together during the pushups, or your feet closer during squats, you have not changed the surface area between you, and the object in question (the ground), has it? After all, the contact surface area (your hands, or your feet) has not changed. Only the separation between your hands or your feet is the one that has changed. So the principle involved does not match the example. I'm not saying that the stability hasn't changed in those cases, but the reason why one scenario is more stable than the other doesn't match the explanation or principle given.

The lack of the subtle understanding of these basic physics concepts is what separates between a superficial knowledge of physics versus a deeper understanding of it. We hope that students that have gone through at least an undergraduate/intro level physics classes in college can acquire the latter and spot the differences in such subtle understanding.


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