How Massage Chairs Work

Most massage chairs rely on a combination of motors, gears, rollers and vibrating mechanisms. This kind of chair dates back more than half a century. Over the last few decades they've become much more sophisticated.

The simplest massage chairs use a series of vibrating surfaces to provide a massage. To create the vibrations, manufacturers use small devices that contain a weighted wheel or gear. The weight isn't centered on the wheel, which makes the wheel unbalanced. When the device's electric motor rotates the wheel rapidly, the rotation causes a vibration. Cell phones with a vibrating feature contain a small version of this kind of device. A massage chair needs several of these devices to generate vibrations across its surface without unbalancing the entire chair.

While no two massage chair manufacturers use the exact same design, there are some general design techniques that apply to most models. If you were to strip away the upholstery of the chair, you'd see a frame that supports a system of motors, gears and rollers.

When you're getting a massage from a massage chair, it's the rollers that act like a human's hands. The rollers move in patterns determined by the structure of the frame. Some massage chairs rollers have a limited range of motion -- they can only move up and down the back of the chair because they travel along a track attached to the frame. Electric motors provide the energy for the rollers.

Other massage chairs have more complexity. On these chairs, the manufacturer mounts the rollers onto a mechanical arm that can move laterally as well as vertically. This means the rollers can move left and right, or even in circles. Again, an electric motor powers the mechanical arm's movements. A microprocessor in the massage chair stores recorded patterns the manufacturer pre-programs into the chair.

Many massage chairs allow the user to adjust the intensity of the massage. There are two main ways to adjust the intensity. One is to change how far the rollers move away from the frame when in massage mode. The second is to mount the frame on a pivot in the backrest, allowing it to move closer to or further away from the user's back.

Since many massage chairs are recliners, manufacturers have to design electrical and mechanical systems that can operate in multiple positions. Some massage chairs have a motorized reclining system. The user can change the chair's position by pressing a button on the massage chair's control system. Other chairs require the user to pull a release handle before physically pushing back against the backrest of the chair.

Not all massage chairs rely on a purely mechanical approach. One design uses water, yet users stay completely dry. How does that work? Find out in the next section.

One alternative to the purely mechanical approach is to use water. That's the principle behind the design of the Hydro-Massage Chair invented by Frank J. Arzt. Arzt's design allows the user to experience an invigorating massage using jets of water, yet remain perfectly dry.

His design includes a waterproof membrane similar to the kind found on a waterbed. The backrest for the chair contains the membrane. The front of the membrane -- the side that is in contact with the user's back -- is restrained by a series of bars. Without the bars, the membrane becomes misshapen whenever the pressure of the water inside it changes. Valves at the top end of the membrane allows users or the manufacturer to fill the membrane cushion with water.

Along the back of the membrane are a series of nozzles. The nozzles connect by tubes to an electric pump, and a heating and cooling system. The pump re-circulates the water inside the chair, pushing it through the nozzles to create the massage sensation. The user sits back in the chair and receives a massage from the water jets. The heating and cooling system can adjust the water's temperature to the user's preference.

Arzt's patent suggests that the nozzles could include a rotor inside the nozzle's central passageway. The rotation of the rotor causes the water jet to rotate as well, increasing the area of impact on the user. By pulsing the water through the nozzles, the chair could simulate the tapping sensation you can get from some mechanical massage chairs.

Although Arzt filed his patent in 2000, the market hasn't been flooded -- pun intended -- with hydro massage chairs. This could be due to the fact that massage chairs are still a small market for much of the world or perhaps the manufacturing process is too complex. But there are dry hydro-massage tables and mattresses on the market, so we may still see a chair variation in the future.

Some massage chairs use another technique that relies on air. How do massage chairs use air to relax an aching back? Keep reading to find out.

A common technique used by massage therapists is to grip and squeeze large muscles firmly for a few seconds before releasing them. This can help relieve tension in tight muscles, prompting them to relax. Some massage chair manufacturers saw an opportunity to incorporate these techniques in their own products. But how do you make a device that squeezes a user without turning it into a dangerous machine better suited for a horror movie?

One solution is to use airbags. Several high-end massage chairs have multiple airbags. Two main areas of concentration are the user's arms and legs. That's because it's easier to isolate the extremities. It's also not likely to injure the user or hamper his or her ability to breathe.

Some massage chairs use multiple airbags to squeeze each arm and leg. A small air compressor inside the chair inflates the airbags. The air compressor connects to the airbags through a series of pipes or tubes. Some massage chairs include a switch that opens and closes air passageways so that the chair can inflate one set of airbags without affecting others. Other massage chairs use multiple compressors, each dedicated to a specific set of airbags.

A multiprocessor built into the chair connects to the compressor and tells it when to activate airbags during a massage. Some massage chairs allow users to adjust the intensity of the air massage. Intensity is proportional to inflation -- a fully-inflated airbag will provide a firmer squeeze.

Some massage chairs use airbags in the seat and backrest as well. By rapidly inflating and deflating the airbags, the chair can simulate the tapping method of massage. Inflating the bags at a slower rate simulates rolling or kneading. But most massage chairs rely on mechanical means to provide most of these features and use airbags as a supplemental massage device.

­How do you control a massage chair, and what's up with chairs that can sense your body size? Find out in the next section.­

Many massage chairs come with a pre-programmed list of massage therapies. A user sits in the chair and selects whichever therapy he or she wants from a list, usually using a remote control. Since there is little or no need to operate a massage chair remotely, most massage chair remote controls are wired directly to the chair.

A microprocessor inside the chair stores the information for each massage pattern. When a user selects a particular therapy, the microprocessor sends commands to the chair's various massage apparatuses. Though a user can't modify a chair's massage patterns, many chairs allow users to adjust the intensity of the massage using the remote. The microprocessor then sends commands to the appropriate apparatus, which adjusts its intensity.

Some chairs have complex interactive devices. If you shop around for a high-end massage chair, you might see one that includes an infrared body scanner. These scanners are really just a series of infrared sensors that can detect at what points a user's body comes in contact with the chair. The sensors send the information to the microprocessor, which then makes some calculations and sends new information to the massage apparatus.

Since several people might use the same massage chair, it's important to be able to make these adjustments. For example, a six-foot (1.8-meter) tall user's back will make contact with more of the chair's backrest than a user who is only five feet (1.5 meters) tall. A neck massage for the six-foot tall user would likely feel very odd to someone much shorter -- if they were tall enough to feel it at all. By scanning the user's body, the chair can adjust so that the points of contact for each person are the appropriate height and width.

Some massage chairs monitor the user's responses to the massage, adjusting intensity and concentrating on specific areas on the fly. The Sanyo Zero Gravity Massage Chair includes sensors that monitor galvanic skin response. This is the same sort of technology lie detector machines use to monitor a person's response to questioning. The galvanic sensors measure the user's pulse rate and perspiration. When the chair detects an increase in these metrics, it interprets the data to mean that the area currently being massaged is particularly tense or stiff. The chair's microprocessor alters the normal pattern to spend more time on that area [source: Sanyo].

A few massage chairs include voice-response software. This software can interpret and respond to vocal commands from the user. The list of commands is usually a small subset of the chair's overall capabilities.

Will massage chairs ever move out of the luxury market and become common in households across the United States? That's the hope of many manufacturers. But for now, it looks like the price of massage chairs will continue to limit the size of the market.

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