It seems every other day, a new "30 Day Fitness Challenge" is being posted on Facebook, YouTube, Twitter, or other social media sites and blogs. But with all of these different challenges out there, how do you know which is the right one for you? We're going to look at some of the different challenges out there and determine which are the best for helping you to kickstart a fitness routine, reach a goal that has been tough to get to, or help you break through a plateau.

The concept behind the 30 Day Challenge is pretty simple and straight forward--do something exercise- or health-related every day for 30 days, and voila! You get results. But why does it work? To break it down, these 30 Day Challenges work because, if done right (meaning each day for the 30-day period) they maximize the body's ability to adapt and change (muscle confusion) resulting in a change (more muscle, less fat, stronger legs, etc., depending on which challenge you do).

For example, the 30 Day Plank Challenge, the most popular one according to 30DayFitnessChallenges.com, requires you to complete a plank (abdominal/core exercise requiring strength and stability) and increase the time that you hold the move each day over the thirty days. This increase in time (or in other challenges, the number of repetitions you perform) will help to build up strength and definition in the challenge's targeted areas.

So which challenges are worth your time and effort? Here are some that you may want to think of, and why they may be good for you:

1. 30 Day Squat Challenge

You will not only be able to build lean muscle in your legs and butt, but the squat challenge is also good for helping to tighten up your core and abdomen.

2. 30 Day Plank Challenge

Because planks are one of the best abdominal and core exercises you can perform, this challenge will help flatten and tone your abdomen--perfect for bathing-suit season.

3. 30 Day Arm Challenge

Combining tricep dips, push-ups and mountain climbers, the 30 Day Arms Challenge is great for toning your triceps, biceps, shoulders and forearms to help eliminate the "bat wing" or arm flab that can plague beach-goers.

There are more 30 Day Challenges besides the three listed here, including other abs, arms and squat variations. Utilizing the training principles of exercise (including increasing repetitions and length of time completing exercise) allows the 30 Day Challenges to be built upon scientific principles of exercise. They are also effective ways to help incorporate and increase body composition change through exercise. I would encourage you to check them out at 30DayFitnessChallenges.com, regardless of whether you're looking to boost your training regimen or get into one for an event or upcoming vacation you may have. These challenges are a great way to get in shape without having to invest in a gym membership or expensive exercise equipment, too.