"I started my descent, came back up, adjusted my back for the next rep—then everything went black," Darin Johnson told Newsweek.

What is a sissy squat, and what happens when you do 100 reps every day for one week? Our writer found out with this squat challenge.

When done with proper form, squats tone your quadriceps, hamstrings and glutes. Learn how to do a squat, plus squat ...