Cyclists normally shift one gear at a time, most have never heard of double shifting. So what is it, and how does it help?

Double shifting refers to shifting on the front chainring and the rear derailleur simultaneously. Most cassette clusters are not spread out for loaded touring. While touring my knees felt stress every time I shifted, until I learned to double shift. For example on a hill I was in the middle ring up front and the 2nd largest cog in the rear, I would then shift into the small ring up front and 3rd largest cog. The double shift allows for smaller gaps between gears, which was much better for my knees. I no longer felt any stress while shifting. I would encourage everyone try it while touring.