The "Rest Step" is a technique used by mountaineers to slow their cadence, rest their muscles, and preserve their energy while hiking on steep terrain at high altitudes. Essentially, the “rest step” takes pressure and strain off your muscles and transfers it to your bone structure.
Although it’s mainly useful on snow, or on climbs at elevation where endurance is important, it can be employed on any trail with steep slopes. It’s worked quite well for me on many trails in Glacier, Colorado and the Grand Tetons in recent years.
Here’s how it works:
As you step forward on a climb, lock your rear knee and keep all of your weight on that rear leg. As you’re swinging your other leg forward, relax the muscles in that leg. Once your forward foot comes to rest on the ground, keep it relaxed so that there’s no weight on it. You can stop in that position for as long as you need to. When you're ready to take the next step, shift your weight to the front foot, step forward with the other and lock the rear knee again, and repeat the entire process.
The locked rear knee provides support for your weight without requiring help from the leg muscle. That means your leg, hip, and back muscles get a rest, if only for a short moment. Stay paused in that position for however long it takes to avoid running out of breath.
In this short video Ward Luthi from Walking The World demonstrates how this technique is put into action on the trail:
A mountain climber in the Himalayas may stay motionless between steps for 10 seconds or more. At lower altitudes, you might only need a half-second pause. The key is to get into a steady rhythm of doing the same thing for each step you take. You can adjust the cadence and the length of your stride according to the steepness of the terrain.
Continuous movement is a great strain on your muscles. Moreover, stopping and starting, slowing down and speeding up, wastes energy. The key to preserving your energy for the long haul is to be the tortoise, rather than the hare.
You can quickly get an idea of how this works by practicing on your steps at home. The benefits are especially clear if you can try it after a long hike, run or bike ride when your leg muscles are already tired. Go up the steps as you normally do and you’ll probably feel a little bit of a burn in your quadriceps. Now, try the rest step and notice how the burn is substantially reduced.
Hiking in Glacier.com