Muscles in your back are designed to stabilize the spine. My first priority in coaching is to teach proper abdominal bracing and to learn to hip hinge. If you’re pulling muscles or cramping anywhere in your torso then it almost always means you’re using spinal stabilization muscles (designed to be static during movement) to move weight. Deadlift, for example, should involve glutes and hamstrings as primary movers and there should be ZERO change in spinal position, ESPECIALLY at the lumbar spine. I drill into my members that deadlifts, cleans, snatches, KB swings, and anything that involves hip extension should NEVER cause fatigue or dynamic stress on the back muscles. So… http://breakingmuscle.com/mobility-recovery/how-are-we-still-getting-it-wrong-abdominal-hollowing-vs-bracing; check that article out and work on stabilizing your lumbar spine and hip hinging. That’s my 2 cents anyways.