I'm finding the hardest part of workouts like afterburn is the lactic acid building up in my legs. It's not that I'm so out of breath that I can't keep up it's that in some of the squats series my leg just won't bend anymore because they are burning so bad. I thought my legs where strong and had great endurance, I don't know how Cathe in the crew just keep going. Is anyone else having this problem or do I just need to work on my leg endurance?