If you want to talk about a love-hate relationship, gravity is a perfect example. Without gravity, life couldn't exist as we know it. The comedian, Thomas Wright, jokingly said: "It's a good thing we have gravity or else when birds died, they'd just stay right up there. Hunters would be all confused." Seriously, though, in spite of the obvious benefits, gravity can take a toll on the human form, especially in the form of awkward postures.
Consider a childhood experience: your grade school teacher, or your mother, reminding you to "sit up straight". By "straight", they meant what we now call a 90-degree posture, which refers to the angle between the torso and legs. It's a problem, though, because it's not the body's natural position. And sitting in such an unnatural posture causes all kinds of problems, as demonstrated in the growing tide of repetitive stress injuries.
But what is the body's preferred position? It would be easy to guess that a 180-degree (i.e., flat) posture is best. After all, that's the posture we use when we sleep, right? As it turns out, the flat posture is also an imperfect posture, which is why we suffer from sleeplessness, tossing and turning all night, trying to find that elusive, natural position that will be most comfortable.
What about walking upright? In truth, the upright posture is actually closer to the body's preferred position, rotating the spine into the proper S-shaped curve. But the 180-degree posture really is not the body's natural position, whether you stand it up straight or lay it down flat.
To find the body's favorite posture, it may be best to go back to another childhood experience-swimming lessons. The first exercise we encountered in the pool was the Dead Man's Float. There we were, bobbing in the water in a relatively relaxed position (except for holding our breath), unknowingly simulating the body's most natural, stress-free position. Jacques Cousteau's description of a floating posture that defies the confines of gravity does, in fact, capture the essence of what our bodies prefer. The natural posture was studied extensively in the 1970's, during NASA's SkyLab experiments. In fact, the space agency actually did a number of underwater buoyancy tests on posture, using submerged and blindfolded astronauts in a "partial-G" environment to simulate the weightlessness of space. During the SkyLab missions, the space agency collected a variety of anthropometric data pertaining to the exact effects of weightlessness on the human form. Some of the effects the studied happen over time, like the deterioration of muscle mass. But other effects are instantaneous, the most notable of which is the unique posture the body assumes in the absence of gravity.
