Not sure but woke up with a stiff back. Did some low bar squats. Skipped the DLs. Drove to work. Got out of car and my back was like, "Fuck you. I'm out! Peace!" Rested for 3, 4 days. First 2 days with ice. Been using a heat pad. Should heal up within a few days. Squats and deadlifs, here I come!