One of the most challenging postures in Bikram- for me

As yoga practitioners, each of us have challenges that are different from the person next to us, based on our fitness level, flexibility, BODY mechanics etc. In Bikram yoga (the style I'm currently undertaking), there is a posture called Utkatasana, or Awkward style. This posture has emerged for me as the most difficult, while a quick glance around the studio seems to indicate I'm in the minority here. Utkatasana is when one bends his/her knees so their thighs are perpendicular to the floor while standing on your toes, your arms extended forward parallel with your thighs. Here is an image illustrating the pose:

For me, I simply cannot hold this pose for longer than a few quick seconds before my legs start to wobble and collapse, like the ground is shaking violently beneath me. Frankly it's rather embarrassing when most people seem to have no issues with it. Hmmm.