Given enough time, all machines will break. Your body is a complex machine. Ergo ...

Engineers have long tried to improve on our perishable meaty parts. Tools, weapons, and armor came first. Powered exoskeletons have emerged in the last five years, offering a glimpse at a future when wearable robots will be commonplace. But examples from the current generation of commercially available powered exoskeletons are heavy, cumbersome, and expensive. Those tradeoffs are easier to overlook for people living with paralysis, but for able-bodied individuals looking to increase strength and endurance or reduce day-to-day bodily stresses, powered robotic suits are nowhere near ready for prime time.

But unpowered or passive bionic devices, which are beginning to creep out of the lab, offer a tantalizing alternative. Compact and comparatively inexpensive, these devices use clever engineering to reduce strain and increase biomechanical efficiency without the use of motors or batteries.

One of the newest examples is a bionic knee brace from Canadian startup Spring Loaded Technology.

"Our brace stores kinetic energy as you bend your knee and then releases that energy when you straighten your leg," says Chris Cowper-Smith, CEO of Spring Loaded, which plans to release its adjustable Levitation brace in early 2016. "It's a simple concept, although the engineering behind it is very involved."

The potential market for a knee brace that can reduce strain and enhance biomechanical efficiency and performance is huge. If you're an athlete or over fifty, or if you're carrying around a few too many pounds, it should come as no surprise that we're a creaky-jointed species. Some 52.5 million Americans suffer from arthritis and with rising life expectancies your risk of knee osteoarthritis is a cringe-worthy 45%.

The Levitation brace uses a liquid spring. Despite what they taught me in science class, some liquids are indeed compressible. Springs like the one in Levitation utilize that property to store and release energy.

"Our engineering went into miniaturization," Cowper-Smith tells me. "We tried metal springs, tried polymers, tried gas springs. In the end we found that a liquid spring enabled us to come up with a device that was compact and powerful."

The brace feels like a shock absorption system. When you squat you can hold the position with minimal effort. You feel buoyant. When you initiate movement the brace will help propel you upward as though you've lost 50 or 100 pounds. It's being marketed at athletes to improve performance and as an off-the-shelf medical device to help those with joint pain.

The brace brings to mind an unpowered bionic boot developed by researchers at Carnegie Mellon and North Carolina State. The device uses a passive clutch to activate a spring held in parallel to the Achilles tendon. It can reduce the metabolic cost of walking by 7%, an energy savings roughly equivalent to removing a ten pound backpack.

"The unpowered exoskeleton works in parallel with your muscles, thereby decreasing muscle force and the metabolic energy needed for contractions," said Professor Greg Sawicki of North Carolina State, one of the lead researchers.

Before the researchers published their findings, there was healthy debate among biomechanical researchers about whether a passive device could substantially increase the efficiency of a natural gait. That debate has now been settled, and it could mark a new era of off-the-shelf devices that reduce load and strain.

Such devices are already seeing limited use in industry. Swiss startup Noonee developed what it's calling the Chairless Chair. The wearable device helps industrial workers avoid repetitive strain injuries by allowing them to effectively sit down while maintaining a standing position. It does this by passively redirecting the person's weight to the ground. The device is getting a trial run in an Audi manufacturing facility.

Ekso Bionics, a leader in the development of powered exoskeletons, also recently unveiled a passive full-body exoskeleton for industry. A heavy tool, such as a grinder, can be fitted to an articulated arm on the suit. The device mechanically counterbalances the weight of the tool and the suit passively passes the load to the floor. The tool becomes weightless from the perspective of the worker. That's a great benefit to ship builders and construction workers who risk strain injuries by hoisting heavy tools all day.

Another powered exoskeleton developer, Cyberdyne (no relation to the doomsday-heralding creator of Skynet), is testing a passive lumbar support device for airport personnel who have to hoist heavy bags all day.

The Levitation knee brace may prove to be the canary in the coal mine for consumer versions of these types of devices. If it does well, we're likely to see a lot more passive bionic aids. Levitation is expected to cost around $2000. That's not cheap, but it's a fraction of what a robotic brace would cost. It's also expected to be 80% reimbursable under most insurance plans.

If you're just hoping to run faster and jump higher, you'll probably be paying out of pocket.