When your client is able to hold a plank for a two min – it’s time to check your client plank form 🙂
I agree as well with most of the responses on here. One minute is a sufficient time to hold a plank. With that being said, I try to get clients to contract every muscle in their body while they are doing that one minute plank (with quality form). Once a client can do a plank for a minute, you add a progression to make it more difficult. Lifting a foot up, reaching a hand in different planes, putting them in a TRX, plank on medicine ball or stability ball. Any way to increase the challenge (within reason). One a client goes past a minute, it is just for fun to see how much stronger their core strength has increased.
Once I had a client who could hold the plank for 9.5 minutes. She was out of the norm, but she had done countless of core strengthening exercises for many months prior to this test. I’m like Paul, I’m not big fan of this exercise either. I do agree that 1 minute is a good time to have as the threshold before advancing to more challenging strengthening exercises and conditioning of the core.