A frequent question I get from customers looking for a massage chair is whether or not a particular model has zero gravity. When I say that most do nowadays, they usually nod in approval. However, when they are sitting in a chair, they will invariably ask me “so, what is zero gravity?”
It is a term thrown around quite loosely in our industry because pretty much every chair has it. But, like 3D/4D and L-track vs. S-track, it’s not always immediately clear what it even is or means. I hope to shed some light on it in this article.
According to Lexico (Oxford Dictionary), the definition of zero gravity is, “The state or condition in which there is no apparent force of gravity acting on a body, either because the force is locally weak, or because both the body and its surroundings are freely and equally accelerating under the force.”
Now, when we think of zero gravity, we usually associate that with astronauts and weightlessness in space, which would fall under the first half of the Oxford definition, i.e. “…the state or condition in which there is no apparent force of gravity acting on a body…because the force is locally weak [like in space].” But obviously that does not apply to sitting on a massage chair with earth’s gravitational pull getting in on the act.
The second part of that definition sounds more relevant to a massage chair user because in a zero gravity position, although gravity is still a force…”both the body and it’s surroundings are freely and equally accelerating under the force.” In other words, the body is positioned in such a way that, in a zero gravity position, the body’s weight is more equally distributed relative to the gravitational pull. Let’s talk more about astronauts (and NASA) to see how it all comes together.
The term zero gravity was first introduced to the massage chair industry by Human Touch when it coined it’s “Perfect Chair” a zero gravity chair. According to their website, the chair’s “ergonomics are inspired by the neutral body posture chaise position developed by NASA to support astronauts during their ascent into orbit.” That was the genesis of the term “zero gravity” in the massage chair industry and it has since exploded to the point where pretty much every chair model introduced to the market has the zero gravity feature.
So, we have defined the term “zero gravity” and we have ventured into it’s origin in the massage chair world…but, again, what exactly is it and how is that incorporated into a massage chair?
From my research on the web (the most trusted source of in the world?), I found out that NASA has determined that a body in zero gravity/neutral body position has the following side view measurements: a.) the seat is tilted up at approximately 30 degrees from horizontal, b.)the articulation angle between the chair back and the seat is 128 degrees, c.) the head is tilted forward 24 degrees, d.) the forearms are articulating at a 124 degree angle with the shoulder, e.) the calves are at a 133 degree angle with the thighs, f) and the feet are at a 111 degree angle with the shins. From straight on, the upper arms in a neutral body position would be about 39 degrees outward from the center line of the body. Each of these measurements have margins of error – in other words the true measurements can be within a few degrees more or less than the figures given above and still be considered within normal range (see the diagram below).
(Many folks believe that zero gravity includes having the legs and feet positioned above the heart. That is evidently not true. Although no one would argue that raising your legs and feet above the heart is a healthy thing to do, it is not part of the zero gravity/neutral body positioning.)
It is these measurements, in part, that play a role in the zero gravity positioning of a massage chair. The neutral body position minimizes the effect of gravity on the spine by spreading out the weight distribution of the body relative to gravitational pull. In other words, the weight of the body is evenly distributed so that no one or two points carry the entire weight of the body, let alone an unbalanced amount of that weight. If you think of sitting in a regular kitchen chair, all the weight of your body is forced down onto the seat. Zero gravity or neutral body positioning reclines you to an optimal position wherein the body weight is evenly distributed along the length of the chair. That is what a massage chair tries to do.
I can say that pretty much all massage chairs try to get the seat and chair back angles right, but I can’t say that all of them get the other measurements right. Most chairs with zero gravity have the calves to feet angle higher or lower, the arm angles (side and front view) higher or lower, and the foot to shin angle lower. They aren’t uniform across the board, but the torso to hips measurements usually fall within the normal measurement (taking into account the margin of error). When a massage chair is in a zero gravity position, the chair and body are reclined back.
But, what about 2- or 3-stage zero gravity, which is available on some chairs? Well, those other positions are usually further reclines beyond the “true” zero gravity position. They are nothing special or notable other than helping you recline further with the simple touch of a button. But those other positions are not really zero gravity positions at all. In other words, those additional “zero gravity” settings don’t distribute the body weight of the user as equally as a true zero gravity setting.
I hope this makes some sense and doesn’t confuse you more!
Dr. Alan Weidner
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