The above photos and and video link show what is considered by many to the traditional Brazilian Crunch. Essentially you are getting into a Front Bridge/Plank and then tuck up one knee. When the knee is tucked up under your chest, then twist that leg under your body. Your torso also twists. Now you do activate your core doing this style of Brazilian Crunch because you are in a plank position, however, many physical therapists and experts would agree there is a better way to strengthen your core than with this twist.
The beginning of this version is identical to the traditional version. The first movement is also the same – the knee tuck. Here is where things change. Remember, in the traditional version, this is where that twist come into play. However, with the alternate version your torso and hips do not twist at all. The only thing twisting is your knee. If you tucked up your right leg, then what you do to finish the movement is twist your knee so your right foot comes up towards your left arm. Mentally, think about touching your right foot to your left elbow. You won’t get anywhere near there, but this is the direction you are taking. Your right knee never comes out of alignment with your right shoulder (no hip or torso twisting). Think of your right knee coming straight forward and then your right foot swinging inside towards your left elbow. Return to the start position (Front Plank/Bridge) and switch legs.
It is up to you, but whenever you see “Brazilian Crunch” in one of our workouts, you have my official permission to use either version. However, I suggest you do the alternate version, as there are no disadvantages as compared to the traditional version. I feel there is only advantages.