There's a little more than a week left to the Plank Challenge I'm doing. Recently, I've held a 4 minute plank but I'm planning to get to 5 minutes by the end of the month.
I know I already have strong abs... you just can't see the muscle through the skin. I do a lot of sit ups, crunches, side planks, mountain climbers, etc. I do think my abs are noticably better, but I know it takes time.
The muscles are looking good in my arms too. I'm still strength training 5 times a week. It is really making a difference and I'm happy with the results so far! It takes a lot of work to keep in shape, but my belly keeps me motivated as I try to get six pack abs. I think if I didn't have the loose skin, I wouldn't have gotten the muscles I have now.
I'll update again as I get closer to my goal of 5 minute planks. Doing planks are never easy... it seems to take forever while you're doing them but I do feel like I have a stronger core as a result of doing them every day during the challenge.