Another abdominal exercise that uses just your bodyweight, Ankle Wiggles is a great movement that uses constant tension in order to crank up the intensity.

Be sure to visit Fitness Generator to get access to almost 2,000 exercise graphics as well as instructions on using bodyweight, dumbbells, kettlebells, resistance bands, and more!

Ankle Wiggles

The initial movement is similar to a standard crunch, only your hands are on the floor at either side of your body. Once in the "up" position, you remain that way throughout the entire exercise, which puts constant tension on your abdominal muscles, and you will really feel it in the upper ab rows.

To execute the movement, you simply slide your body to the left and the right, using one hand at a time to reach down all the way until you touch the heel on that same side of your body. Once you touch your heel, immediately reverse direction and slide all the way over to the other side, touching the opposite heel. Complete for an equal number of repetitions on both sides of your body, and be sure to keep your head and shoulders completely off of the ground during the entire movement.

Click here to see more exercises that use just your bodyweight.