Dr. Stuart McGill has the "Big 3" core exercises that develop core strength without stressing your spine. For each exercise, a rep is a 10-second hold. In his book "The Back Mechanic" he says it's important to use similar reps for each exercise so that you don't have imbalance problems. I'm confused what is the correct balance for the side planks.
From page 105:
... hold one side 10 seconds, roll to the forwards plank on the elbows with no spine twist, hold for three seconds, then roll to the other side. That is one repetition.
So does [left, center, right, center] constitute two reps or one rep?
It seems from the quote that it would be two reps. But each side is only getting one rep. I'm not sure which is the right amount to balance with the same number of reps for the other exercises in the series (the curl-up and bird-dog).