What are some workouts that will challenge my muscles?

Insanity/P90X: Pizzawizardii, I am training for 2 tough mudders this year and i love shaun t's insantity, which require no equitment but an excellent pair of sneakers and p90x which challenges you at your own pace. Be sure to check with your physician before starting a workout program, however, either of these will challenge even the most fit person. Best of luck!