Exercises from the community
Reverse Crunches (abs)
Reverse Crunches specifically target the lower abdominals by moving the hips and pelvis instead of the shoulders, filling a gap that standard crunches don't reach as directly. Lie on your back with knees bent and feet off the floor. Curl your hips up and in toward your ribcage using your lower abs, then lower back down with control, stopping before your feet touch the floor to keep tension on the muscle.
Running
Hip Raises (abs)
Hip Raises use the weight of your legs as resistance to boost lower abdominal muscle growth, with a straighter leg position than the bent-leg variation for a longer lever arm. Lie on your back with your legs extended straight up toward the ceiling. Contract your lower abs to lift your hips a few inches off the floor, then lower back down slowly without letting your legs drop or swing.