Rounding of the lower back is considered very poor form in weight lifting. It can lead to and aggravate severe and catastrophic injuries like bulging or herniated also known as slipped discs. If you are a novice or beginner at the gym whom is trying to strengthen their back after such an injury it is very important that you have good lower back form or position when lifting. The following is a list of key techniques to stop your back from rounding and keep you safe while training.
Step 1 - Improve your actual lifting technique
In the deadlift pull the bar back to your shins and put your weight in your heels. Now lift your chest to the ceiling while drawing your shoulder blades to the opposite back pockets, this will help increase the activation of your lats and trapezius thus stabilising the mid to lower spine and increasing your efficiency . In a squat be sure to draw the bar down onto your shoulders its counter intuitive but it will activate your lats and help stabilise the lumbar
Step 2 - Film the lift from the side
Use your phone to film your deadlifts or squats. You can then see your improvements and faults in your lifts especially as you begin to fatigue over a training set.
Step 3 - Increase the muscle / tendon length of the hamstrings and sciatic nerve adherence
The hamstrings attach to the bottom of your pelvis at the sit bones and your pelvis to your lumbar spine so if the hamstrings are tight or the sciatic nerve is caught then this can cause posterior tilt of the pelvis and rounding of the lumbar spine especially at the bottom of squats and deadlifts . To help lengthen your hamstring try static or dynamic stretches that also improve neural mobility, this will allow for your pelvis to sit in an anteriorly rotated pelvic position and thus ensure a good neutral lumbar spine in lifting . The best stretches are standing forward bends at the end of Jefferson curls with a light weights up to 5% of your body weight . Jefferson curls not only help you improve inter vertebral muscle stabilizer strength and endurance but they also help lengthen hamstrings. Also try lying on your back and gliding your sciatic nerve with Monster bands . This will improve hamstring muscle and sciatic nerve tension and enable better position at the bottom of your lifts .