Open workout 17.1, otherwise known as Biering- Sorenson told you so…
Across the board, from beginner to elite, the most common comment I saw regarding the 17.1 WOD is the after effects of a tired, tight, and/or downright painful low back.
From what I observed, in the handful of people I saw doing the WOD, the reason for this is the natural rounding of the low back that occurred as every competitor reached fatigue.
We spend the overwhelming majority of our time during workouts attempting to maintain midline stability, keeping our backs 'set', and engaging our posterior chain. During CrossFit, and weightlifting, a rounded low back is a crime punishable by a beating with a PVC stick and lots and lots of burpees.

The problem occurs when we get appropriately fatigued, and start losing our midline stability and 'set' back during intense efforts like those displayed during the 17.1 WOD. Because, as we know, if we don't train the movement we will not be very good at the movement.

This is where the Biering-Sorensen, otherwise known as the back extension, exercise comes into play. During the 17.1 WOD the risk of low back rounding potential increased as people approached 150 reps. So the only way we could have prepared for 150 rounding of the low back, is to practice 150 roundings of the low back. Which most people do not.
If you know me, and my cohorts at SODO CrossFit – Darrick and BeckyJo - you know that we preach the gospel of high repetition back extensions. And now you know the reason.
When performing a back extension repetition properly the pelvis and hips are blocked and the majority of movement comes from the low back. This is very similar, if not the same, as the rounding of the low back that occurs normally during high-intensity workouts and/orcompetitions.
In addition, from a performance standpoint, if you felt as though your low back was limiting your ability to go longer or faster during this particular work out, that most likely was the cause. So high rep back extension training, could have prevented the post competition low back blues, as well as improved your performance.
So, it's too late now for 17.1, but going forward remember that back extensions, specifically higher repetitions (in the 100+ range), are not just for clinical low back pain treatment.