How to do Air bike crunches
Begin lying on your back with your legs bent up in the air at 90-degrees with the toes pointed. Place your hands behind your head with the elbows out to the side.
Tuck your chin toward your chest and then crunch up and forward as you lift your head off the ground. Press your belly button toward the ground as you tighten your abs.
Next, kick one leg out straight away from you. As you do so, crunch the one elbow toward the bent knee as you twist your head and shoulders that direction.
Then, bend your straight leg back in and return your head and shoulders to the center.
Repeat for the desired repetitions, alternating sides.