Zero Gravity or Not – That is the Question!!

astronautZero gravity has become a very popular feature among massage chair models and among massage chair shoppers. I get asked all the time about whether a particular model has zero gravity or not. Funny thing is, most folks think they want it but have no idea what it really is!

But, is zero gravity something that you really want in a massage chair? I will define it and then explain to you the pros and cons of zero gravity, especially as it pertains to you, the user, and your therapeutic experience with or without it in your massage chair.

In physics, zero gravity is defined, essentially, as weightlessness. However, zero gravity as it pertains to seating is defined by two conditions:

  1. 1. A 30 degree upward tilt of the seat, and
  2. 2. A 120 articulation between the tilted seat and the chair back.

The essence of zero gravity in the seating paradigm is that with these angular articulations, your body and spine are not necessarily in a weightless position (because gravity is always at play here on earth!), but your body is positioned such that it’s weight is evenly distributed throughout the body.

Here is a great image of the Human Touch HT-7450, the first zero gravity massage chair, in it’s zero gravity position. Notice the upward tilt of the seat and the angle of the chair back, relative to the seat.

Zero Gravity Massage Chair

Zero gravity was a feature first introduced by NASA to explain what they found to be the optimal seating position for astronauts who were spending a good amount of their time strapped into their seat in their  spaceship as it orbited the earth.

This becomes apparent when you sit in a normal chair, with a normal horizontal seat and with a chair back that is either reclined or inclined, and then put the chair into a zero gravity position. If you focus on how your low back feels in both positions, you will become very aware of the additional “weight” or compression on the low back when the seat is horizontal. When the zero gravity positioning is introduced, you will suddenly become aware that the weight or compression on the low back shifts and now feels more evenly distributed throughout the whole body.

THAT is the benefit of zero gravity in a massage chair. If you have low back pain, either acute or chronic, you will welcome the “decompression” of the low back that comes with the zero gravity positioning. This feature is fantastic in a non-massage chair. However, in a massage chair, there comes a trade-off and here it is…

The Reach of the Rollers!

Why is it that a chair like the Inada Sogno, that has only a 29″ roller track, reaches lower into the buttocks than does a chair like the OS-7075R from Osaki that has a 31″ roller track? It’s not because the rollers don’t go up as high into the neck on the Sogno. The answer is in the seat positioning!

In an April 2013 article I wrote

“You see, when the seat remains horizontal the rollers have a straight shot from the back down to the buttock area. It is a straight line and the rollers don’t have any additional distance to travel than right from the chair back linearly to the buttock and sacral areas of the seat. On the other hand, the OS-7075R rollers (or the rollers of any massage chair that incorporates zero gravity) need to travel down the distance of the chair back and then, because of the zero gravity positioning of the seat with it’s associated 30 degree tilt up, the rollers have to travel “around the bend” between the chair back and the chair seat and head in a different direction altogether to get to the buttocks area.

We all know that the shortest distance between two points is a straight line (“as the eagle flies”) and if you add a bend in the line between two points, the distance increases. So, when you add a bend in the horizontal line  between the chair back and the chair seat the rollers have a greater distance to travel in the OS-7075R to hit the the same areas that the Inada Sogno rollers hit.”

And, of course, the rollers in a chair like the OS-7075R do NOT hit the buttocks because they cannot travel that extra distance. I hope this makes sense.

In Summary…

So, going back to the beginning of this article, the trade-off with zero gravity is that if you get the zero gravity feature you will have the benefit of relative “weightlessness” or even distribution of body weight, which will take strain and compression off of what might be a very sore low back.

The flip side of the coin is that with zero gravity the rollers will not reach as far into the buttocks to hit the butt muscles, which is an area that, in most back pain sufferers, could sure use some roller massage. If you get a chair with a horizontal seat, the rollers will do more good lower down into the buttocks region.

You have to decide what is more important to you: decompressing the low back with zero gravity or getting roller massage down into the buttocks. Now, what if there came along a massage chair that had a really long roller track that could overcome the distance hurdle of zero gravity and fully offer roller massage to the buttocks area. Well…it’s here. The Infinity Iyashi not only has zero gravity but has a 49″ roller track, which will go way down into the buttocks area even when zero gravity is being used. I think we are going to see more and more of this extended roller track into the seat idea. Best of both worlds!

Dr. Alan Weidner


2 Replies to “Zero Gravity or Not – That is the Question!!”

  1. I’ve had 2 lower back surgeries on L-4/5 ; he had to clean out the ruptured discs. Do you recommend the message gravity over the non-message gravity chair .

    1. Hi, Terrence
      Thanks for reaching out. Zero gravity was designed to evenly distribute the weight of the body in a reclined position. Since you’ve had two surgeries in your lumbar spine, I would think that zero gravity could reduce pressure on your low back thus minimizing the chance for irritation. I hope this helps.
      dr. w.

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