We all keep grinding out sit-ups by the dozen: this one-second movement loads the lumbar discs so badly the US Army dropped it from its fitness test
Full sit-ups compress your lumbar discs with 3,300 newtons of force—exceeding safety thresholds set by occupational health experts. The US Army and Navy abandoned this fitness staple after finding it caused over 50% of test-related injuries, replacing it with safer core exercises that build strength without spinal damage.