Walk across a pool at chest depth and your knee carries less than half the load it carries walking across your kitchen.
Fifty-six percent less, to be exact.
The number comes from twelve people who agreed to something unusual. They had already had a hip or a knee replaced, and their implants had sensors built into them — strain gauges that measured the force going through the joint and transmitted it out, several times a second, while they moved. Researchers in Berlin had them walk, climb, stand and cycle on land. Then they had them do the same things in chest-high water, and watched what the joint reported.
The hip carried about a third less. The knee carried a little more than half less. Those figures came out of a working joint inside a living body rather than out of a computer model, and they were published in PLOS ONE in 2017.
That gap matters if walking is the part that has started to hurt.
The advice and the body it was written for
The standard recommendation is not wrong. Walking is …