This morning I completed the Core Challenge for the first time. I first found out about this a few months ago, and had done part of it, often by doing half the amounts of each exercise listed. You have to do 50 crunches, 15 push ups, 1 minute plank pose, 30 seconds side plank, 1 minute bridge pose, 15 push ups, 1 minute plank pose, 30 seconds side plank, 50 crunches, 1 minute raised plank, 2 minutes bridge pose, 50 crunches.
I did it as soon as I woke up this morning, really went for it, and completed it in about 17 minutes. It was pretty hard! The hardest part is actually the plank pose. After about 30 seconds of holding that pose, it really starts to become a huge strain. That final raised plank was 100% pure willpower, with various grunt type sounds as I really struggled to reach the 1 minute mark.
I felt pretty buzzy for a while afterwards though. A short strenuous workout like that actually ends up giving you energy.