Recent studies show that the human brain has very sophisticated mechanisms in place to control our movements. In order to minimize the amounts of energy a regular downwards arm movements would need, the brain becomes aware of gravity and, instead of tightening the muscles, it rather lets the whole arm fall down, with less muscle control. This also applies to more complex movements.
 

Because gravity affects the body at all times, our very internal structure is optimized in regard to its effects. For instance, the power with which our hearts beat is drastically higher than the power they would need if we were crawlers. Pushing our blood and other fluids upwards through the body requires a tremendous amount of effort, which the body learned to create over millions of years of evolution.
 

During that time, the brain also learned to manage the power very efficiently, so that we wouldn't have to eat or sleep every other hour. Biological and environmental restraining factors are computed into the plan that guides each of our moves, in a way that allows the brain to design the smallest amount of energy to the process as possible. Of course, if we choose to, we can add more power to our moves, by tightening our muscles and asking the brain for more strength.

 
However, the way in which the brain calculates exactly how to distribute power to various types of movements still remains a mystery to scientists. The associations that are formed between neurons, which also store data regarding previous similar movements, allow our "central processing unit" to design our moves in a very energy-efficient fashion.
 

Discovering exactly how it does that could lead researchers to developing new ways of looking at motor dysfunction, as well as new means of treating them or rehabilitating people who suffer from this kind of afflictions. Scientists already proved that mathematical models and predictions can be used to calculate the formulas by which the brain guides itself. Strangely enough, it was these types of calculations that led researchers to the new theory of motion.