Similar to the cross knee, this front knee strike changes requires a little more balance and lot more twisting action from your abs.
How to do it: Start standing on guard, with your right leg behind your body (your right heel off the floor), balancing on your left leg with your left knee slightly bent. Bend your right knee and draw it up in front of you, while you turn your upper body, slightly rounding your back, crossing your left elbow over the outside of your thigh. Hold for one count and then slowly lower, returning your right leg to start position. Repeat 20 times with the right leg, 20 times with the left.
Bonus tip: Exhale forcefully as you cross your elbow to the outside of your knee and draw your abs in as tight as you can to help keep your balance.