If you are ascending a very steep slope and your legs are getting tired you can use the “rest step” to maintain a steady pace. This might include several situations such as a long stairway with a heavy pack, breaking trail through snow up hill or running out of steam at the end of a long day in the mountains. The idea of a “rest step” is to keep a sustainable steady pace versus a stop and start when you get too tired to go on. Stopping and starting on the trail with too many rests is a recipe for low mileage.
I learned the “rest step” from Rainier Mountain Guides in preparation for climbing Denali, the highest peak in North America in Alaska. With heavy climbing boots, crampons, a 60-pound pack in the snow and lowered oxygen as you ascend the slope, every step can feel like weight lifting in the gym. It is easy to get out of breath and develop fatigued legs. An overwhelming urge to take a break can seize you.
To do “rest step” you throw you leg up and pause with your lower leg locked straight. This creates a restful position as all your weight is balanced strait in alignment with your one lower leg. Your weight is held by your bones, not your muscles. The upper leg gets a moment of rest before you step up. You can take as long or short a pause as you need. Get a steady rhythm. A count may help. You can also integrate your two hiking poles and push simultaneously with that upper leg when the pull up happens.
In my experience this is much more sustainable than hiking faster and stopping for frequent rests. Use the rest step when you are running out of steam, or when you have a very steep long slope and your experience tells you that you need to be pre-emptive and not overdo it early in the day.
Another situation where rest step is useful is if you find yourself behind another hiker, ascending at a slower pace from your natural pace. Instead of going into slow motion, count out a rest step and take advantage of the opportunity to rest your leg muscles, tendons and joints. Just slowing down does not provide the same recovery as the rest step.
A couple of YouTube demos for illustration:
Be careful, there are many YouTube videos that very poorly or incorrectly demonstrate the rest step.