About 31 million Americans experience lower back pain at any given time, according to the American Chiropractic Association. Strengthening the core and improving flexibility are among the main fitness goals for those suffering from chronic back pain. Today, finding an effective yet fun workout targeting these regions is easier than ever with your smartphone.

Research shows that 19 percent of all smartphone users downloaded a health-related app in 2012. With millions of apps on the market, how do you choose one that supports your goal? We’ve taken a bit of the guesswork out of it by highlighting a few of the best apps available for increasing flexibility and overall fitness.

Navy Seal Fitness, by Double Dog Studios

If you’ve ever dreamed of being as fit as a Navy Seal, this app is your answer. Featuring a layout that resembles an enhanced e-book, the Navy Seal Fitness app features images of how to perform certain exercises; video content is also included. This app is designed as a comprehensive guidebook, including overall fitness tips on a wide range of topics including exercise physiology, heart rate monitoring, basic workouts, various types of aerobic activity, muscle function, calisthenics and strength and flexibility training. Available for iPad owners, this app is a great choice when you want to learn more about how to improve your strength and flexibility.

Abtastic-HD by 2Dogs.com

Designed to help any person get the rock-hard abs they have always wanted, the Abtastic-HD app includes 15 video workouts specifically targeting the core area. While many may think this app targets the oh-so-vain types who live by the “Gym, Tan, Laundry” motto (made famous on MTV’s “The Jersey Shore”), the truth is everyone benefits from a stronger core of the abdomen, hips back and chest.

iWorkout Pro by Michael Dearworth

Featuring more than 45 different workouts and a randomized workout schedule for each day, iWorkout Pro is the perfect way to improve your fitness level. Constantly changing our workout routine allows for greater overall fitness because our bodies do not simply get accustomed to a specific range of motion. Celebrity personal trainer Chris Powell of ABC’s “Extreme Makeover” says this about the subject: “It actually takes about six exposures to a specific workout for your body to experience all of its benefits.” This app gives users the workout variations needed, while allowing the user to select the difficulty level for each workout as well.

GAIN Fitness Cross Trainer

Want a personal trainer, but it’s not in your budget? The GAIN Fitness app can be the perfect solution. Available for iPad, this free app builds a custom fitness plan for you based on your preferences and your own specific fitness goals. It includes a calendar to track your workouts as well as your caloric intake. The app also features videos of professional fitness trainers and athletes demonstrating a particular exercise move. But get this… when you’re low on motivation, a real person’s voice is there for you, encouraging and motivating you through the slump.

Fitness Builder

Available for both iPad and Android-powered tablets, Fitness Builder is THE one-stop shop for total body fitness. What’s so great about this app? Well, having access to a live trainer is pretty awesome, wouldn’t you say? Beyond that, the app features more than 5,000 exercises and 800 workouts. It tracks user stats (including weight, fitness level, BMI and BMR). The app includes a social media element, as users can post their progress to Facebook and Twitter. With many workout choices, you can easily focus on flexibility and core strength while never becoming bored with the same old routine. Fitness Builder involves a monthly subscription, but an introductory offer is available so users can give it a “test drive” before committing.

Image by Flickr user Maria Ly