Improve your stability and endurance: Doing exercises that challenge new muscle groups is one of the keys to fitness success, so don't be afraid to add a stability ball, yoga, Pilates and other resistance exercises to your weekly routine. These exercises encourage you to focus, concentrate and breathe deeply as you perform each movement; they're a great variation from the usual gym routine and will help you increase strength and endurance as you get through each challenging workout.

Also check out... Prevent Workout Ruts Having Trouble with Your Workout? Get... Fat-Burning Secrets for Cardio Workouts 20-Minute Home Workout

Take it outdoors: Freshen up your workouts by going out for a swim, playing tennis outside or just taking a hike on a trail in the country. Getting some fresh air while staying physically active is a great way to skip your usual workout routine, burn calories and challenge key muscle groups.

You might also find fitness clubs and groups already undertaking these types of challenges in your area -- consider signing up so you have a team of supporters to help you breeze through that next challenge!