Stand with your feet shoulder-width apart and your hands behind your head. For the next two minutes, do this:
At no point can your hands leave the back of your head. Doing so means you either lack the strength through your legs or the mobility through your upper back to complete the challenge.
Keep your chest up. Maintain a strong flat back throughout the duration of the two minutes. Rounding the back means failing the challenge.
The hardest part of the drill is going from a three-fourths squat hold back into a half-squat position. Do NOT stand up during this portion of the challenge! Doing so means you didn't successfully complete the drill. Good luck!