The following infographic from Visual Capitalist compares the most...
If you've ever hiked up a steep hill with a heavy backpack, you'll know how hard it can be on your leg muscles and your knees. Individuals in peak physical condition may be able to withstand this strain temporarily, but sooner or later, fatigue will inevitably set in. Luckily, it's possible to delay this process and preserve your muscles and joints with the right technique.
As you walk uphill, pay attention to how you bend your knees. Without proper training, most of us will default to bending both knees at once—the front leg will bend close to 90 degrees, while the back leg will be almost straight (but not quite locked at the knee). This motion continually puts strain on both legs, since the muscles are the only thing keeping them from collapsing out from under you. It may be fine for short hikes with a light pack, but for all-day backpacking treks, it will become tiring.
The solution is simple, and it's known as the rest step. The rest step ensures that your rear knee is locked straight while your other leg bends forward. By locking the knee, it takes the load off your muscles, and supports part of your weight with your leg bone for a split second with each step. These split-second rests add up over time, and reduce the overall strain on your leg muscles and joints.
Here's a video from Backpacker Magazine that shows how it's done:
When you practice this technique, take it slow and steady, with short pauses between each step. Mountain climbers in extreme conditions may need as much as 10 seconds of rest between steps, but for the average backpacker, half a second per step should be adequate.
Special thanks to Evan J. for showing us the rest step!