Anti-gravity treadmill

The patient walks or runs inside a sealed chamber pressurised around the lower body. Air pressure lifts a precise, calibrated proportion of body weight — commonly down to 20 per cent of normal load — while the legs move completely freely 1. Unlike a harness system, nothing restricts the trunk 1.

Load can be increased in single-percentage steps, which means the progression from protected to full weight-bearing happens gradually rather than in the jumps that crutches impose 1.

After lower limb fracture or joint surgery where weight-bearing is restricted, after ACL reconstruction and other knee surgery, in knee and hip osteoarthritis where full-load walking is too painful to practise, in obesity rehabilitation, and in return-to-running programmes after injury.

Also in neurological rehabilitation for patients who can walk but fatigue rapidly at full load.

It lets someone maintain cardiovascular fitness and walking or running mechanics during a period when full loading is not allowed. That matters because the fitness lost during a period of restricted weight-bearing usually takes longer to rebuild than the tissue took to heal.

Load progression must follow the surgeon's protocol. We ask for it in writing rather than inferring it from the operation name.

Air pressure supports a set proportion of body weight, so running or walking can resume at a load the healing tissue tolerates — and that load is increased in measured steps rather than guessed.

This is most useful after lower limb surgery or fracture, in painful arthritis, and in return to running, where the alternative is a jump from nothing to full body weight.

Knee load falls as more weight is taken off and as walking slows 2. In people with instrumented knee replacements, peak knee force ranged from 5.1 times body weight at the fastest speed tested with no unweighting to 0.8 times body weight at the slowest speed with the load set to 25 per cent of body weight 2. In women with hip osteoarthritis, walking at 50 or 75 per cent of body weight reduced hip pain compared with walking at full weight 3.

Taking weight off does change the way people walk to some degree. In a comparison with a harness system in healthy volunteers, unweighting altered the normal gait pattern in much the same way with both, while heart rate was lower and comfort higher with air-pressure support 4. With more weight taken off, the hips and knees also bend less than in full-weight walking 3. Load is therefore brought back towards full body weight before practice moves to the floor.