Good lower abdominal exercises include the static press at 90 degrees, single-leg stretches, U-boat exercises, leg lifts, hip lifts and twists and frog presses. Those performing these exercises should include rest periods of 45 to 60 seconds between sets.
Exercises such as the 90 degrees static press, single-leg stretches, U-boat exercises, frog presses and leg lifts involve flexing the thighs and bending the knees at 90 degrees or more towards the chest. These exercises use the abdominal muscles to lift the legs. The leg- and hip-lift exercises, which are done while lying flat on the back and using the arms for support, pull in the abdominal muscles.