I think the planks are particularly challenging, and I really like the new oblique stuff Cathe does in the tri/bi video. Check out Jai's form, too--she is so controlled just doing a simple crunch!
Wendy
Yes! I love those planks! They are so tough, but so excellent for strengthening your core. And they are really improving my running. I can feel the strength in my core muscles when I run, which is an unexpected bonus of these workouts!! Thanks Cathe!