Mobility is one of those things you never pay attention to until the day you walk into the gym and realize you've lost some of it. Will have to check this out. For the first time ever, I injured my back and hip flexor doing some heavy leg press work. For years I have been walking in to the gym with like 4 to 5 minutes of warm up and then straight to power cleans or squats and never so much as pulled a muscle. This time, though, I eased the weight down on the leg press and I felt Satan run me through with a rusty pitchfork through my lower back. I know what caused it too. And the lowest loaded portion of the leg press movement, I tried for max range of motion (as I've always done) and my hips rolled up under me as I brought my knees to my chest. Something got hyper extended and- bam- no squats, deadlifts or back work for 4 weeks.