When it comes to ab exercises, variations of the leg lift exercise are a staple for those in the fitness industry. However, why is it that sometimes you feel this exercise in your low back? I thought we were training abs?
Be sure to pay close attention to the entire video for comments and simple explanations in the bottom left corner. Below are some other explanations in more detail...
In terms of anterior musculature, the rectus abdominus and external obliques are responsible for keeping the pelvis posteriorly rotated. This limits excessive low back arching, associated with anterior pelvic tilt. These muscles have to FIGHT against stiffness from muscles responsible for anterior pelvic tilting. This includes the iliopsoas and erector spinae.
Because the legs are being lifted into the air, the hip flexors are being recruited. Without stabilizing the pelvis in a posteriorly tilted position prior to lifting the legs, the pelvis may anteriorly tilt and your low back may arch. This may be why you're feeling this exercise in your low back!
SO be sure to watch the full video, watch for the cues and differences in form, and be sure to follow the tips to perform this exercise! It is important to understand when our muscles fatigue - we lose form. Focus on quality here!! If you're eventually feeling it in your low back, those abs and external obliques may be fatigued.