Not all zero-gravity chairs are massage chairs.

Courtesy Amazon

The Zero-gravity Position

Let's cut to the chase: The chair doesn't defy gravity. Even with all the massage elements running and in full recline, you're not going to fly off into the atmosphere. Nor does the chair hover, float or even lose weight. In fact, according to the user's manual, the chair weighs 200 pounds (90.7 kilograms) [source: HT-7450 Manual]. So what does it mean if a massage chair is a zero-gravity model?

­It has to do with the recline position the chair can assume. The position mimics the posture astronauts take during liftoff on space missions. Because astronauts endure intense and sudden increases in gravity while escaping the Earth's gravitational pull, it's important that they position themselves so that their bodies can deal with the increase in stress. By assuming a reclined position, astronauts distribute the stresses of takeoff across their bodies in a safe way. To that end, the chairs astronauts sit in during launch use this reclined configuration.

An astronaut sits in a spacecraft simulator in the zero-gravity position.

Courtesy NASA

Zero-gravity massage chairs can assume the same position to help distribute a user's weight across the chair. The manufacturers claim that this relieves stress on the body and allows for a deeper, more intense massage experience. Some manufacturers claim that the reduction of stress on your body is so effective you'll feel virtually weightless as a result.

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­While several massage chair manufacturers offer models that come with the zero-gravity position feature, not all zero-gravity chairs are massage chairs. Some furniture manufacturers offer normal chairs that recline into the zero-gravity position. The chairs distribute your weight and support you, but they won't rub away your tension and stress.

Other manufacturers stop short of making that particular claim. Instead, they say that the chair replicates the launch chairs for astronauts. They call their chairs zero-gravity not because of the effect the user feels, but because of the position the chair assumes when activated.

One benefit of this position is that it promotes circulation in the legs and reduces swelling. Elevating the legs over the level of the heart during rest can help prevent conditions like varicose veins [source: VascularWeb]. Of course, you could achieve the same effect by lying down and putting a couple of pillows under your legs. But that's not quite as impressive.

During the author's massage experience -- yes, the author was the weary journalist mentioned earlier -- there was no sensation of weightlessness, but the reclined position was comfortable and did allow for an intense massage. Because the author's back was in full contact with the chair's backrest, the full force of the chair's massage routine was effective. An upright position might not allow the intensity and thoroughness of a massage in the reclined position.

Are zero-gravity massage chairs worth the expense? That's a decision best left to the consumer. Some people might think the chair's convenience and effectiveness makes the expense completely justifiable. Others might prefer to see a human massage therapist -- $4,000 could buy a lot of visits to the spa.

To learn more about massage chairs and related topics, take a look at the links on the next page.