Saturday, May 23 2020
Traditional sit-ups use more of the hip flexor muscles—which attach between the thigh bones and lower back (lumbar spine)—than the actual rectus abdominis (the “six pack” muscle). Since the hip flexors attach to the front of the lumbar spine, if they become overworked or overtightened they can create an anterior (forward) pull on the lumbar vertebrae, which might be the reason for the discomfort.
Another reason for low-back soreness might be the fact that doing sit-ups on the hard floor pushes the spine into a hard surface, which could cause additional pressure on the posterior portion of the spine.
Because sit-ups focus on the movement of spinal flexion and use only a few muscles (the rectus abdominis, the external obliques and hip flexors) in the front region of the mid-section, consider selecting other exercises that use muscles on both the front and back sides of the core. If your back only bothers you when doing sit-ups, skip that exercise and choose others that will strengthen the entire core as opposed to one specific area.
Other exercises that can strengthen the core and help alleviate low back pain include: