The upper body day comes back around with a new opener. Thirty seconds of arm circles and 30 seconds of bicep extensions, three, four or five sets, one minute of rest. Bicep extensions you already know from Day 6; the arm circles are new and considerably less friendly than they look.
Arm circles hold both arms straight out to the sides at shoulder height and rotate them in small continuous circles for the full half-minute. The circling is almost beside the point - what makes this exercise work is that the arms never come down. Your deltoids are supporting the weight of your own arms at their least advantageous angle for 30 unbroken seconds, and the circles simply guarantee you cannot cheat by locking into a comfortable position. Following it with bicep extensions keeps the arms working while giving the shoulders a slightly different job.
Keep the circles small and the arms genuinely level - the moment they drift downward the exercise gets easier and stops being the exercise. Fully extend through the fingertips. On bicep extensions, supply real tension in both directions and keep the elbows from drifting behind your body.
Small circles, straight arms, thirty seconds: the simplest thing in the program and one of the longest half-minutes in it.
Make it Harder: Reverse the direction of the circles halfway through the interval without ever lowering your arms.
Make it Easier: Bend your elbows slightly for the arm circles - shorter levers make the same half-minute survivable.
