Doing CrossFit workouts as prescribed is not a starting point, but a culmination of years of training. The goal is not simply do them as Rx'd, but to do them with high intensity. The best way to get there is to start by doing lighter weights and less reps at high speeds, and then slowly adding weight and reps while continuing to move fast.
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Workout
Jerk 5-3-1 (3 waves)
then,
3 rounds of:
"Barbara"
20 pull-up
30 push-up
40 sit-up
50 squat
rest 3:00