I had a PR FS recently. I have learned much from incorporating singles into my training. First, the core stability that is required to hit a single is much different than what is required when performing doubles and triples. Second, there is great benefit to training the abs with heavy weight and low reps. I have a well rounded core workout and training my abdominals to be strong has really improved my core/trunk stability during the front squat and back squat. The first set is 45 lbs times four reps and the second set is 25 lbs times eight reps.