It’s time to amp up the intensity. Circuit, HIIT, and Tabata training produce killer results in little time. Circuit training involves moving from one workout directly to the next, HIIT is short bursts of intense exercise followed by quick rest, and Tabata (a form of HIIT) is strictly 20 seconds of intense work followed by 10 seconds of recovery for eight cycles. These workouts help burn fat, increase endurance, and improve overall fitnessAerobic and anaerobic changes with high-intensity interval training in active college-aged men. Ziemann, E., Grzywacz, T., Kuszczyk, M., et al. Department of Physiology, Academy of Physical Education and Sport, Gdańsk, Poland. Journal of Strength Conditioning Research, 2011 Apr;25(4):1104-12.Circuit training provides cardiorespiratory and strength benefits in persons with paraplegia. Jacobs, P.L., Nash, M.S., Rusinowski, J.W. Department of Neurological Surgery, University of Miami School of Medicine, Miami, FL. Medicine and Science in Sports and Exercise, 2001 May;33(5):711-7.Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Tabata, I., Nishirmura, K., Kouzaki, M., et al. Department of Physiology and Biomechanics, National Institute of Fitness and Sports, Kagoshima Prefecture, Japan. Medicine and Science in Sports and Exercise, 1996 Oct;28(10):1327-30.Metabolic profile of high intensity intermittent exercises. Tabata, I., Irisawa, K., Kouzaki, M., et al. Department of Physiology and Biomechanics, National Institute of Fitness and Sports, Kanoya City, Japan. Medicine and Science in Sports and Exercise, 1997 Mar;29(3):390-5..The only tricky bit is making sure to keep on top of those timed intervals while also getting on a high-intensity sweat. Forgo fumbling with a watch while staying accountable (yep, rest for only 30-seconds!) and try one — or all — of these cool mobile apps.

Circuit Training Apps

Photo: Circuit Training Timer for iOS

Circuit Training Timer. When a workout calls for 30 seconds of military presses, 20 seconds of calf raises, and a mere 10 seconds of recovery, who has time to worry about keeping time? Luckily, users can plug in their circuit workout to a “T” and let Circuit Training Timer let them know when it’s time to stop n’ go. Cost: $0.99, compatible with all iOS devices.

Intervals. From squat to sprints, users can easily customize intervals and circuits for the perfect heart-pumping workout. Features include various audio settings, warm up and cool down options, and a CrossFit WOD timer. Cost: $2.99, compatible with iPhone and iPod Touch.

Interval Training Apps

Photo: Bit Timer for iOS

Bit Timer. Probably the sleekest application of the bunch, Bit Timer cuts out the bells and whistles and goes for simplicity. Users plug in three main settings: work, rest, repeat. But heads up: The app only allows for a maximum of four-minute intervals — so Bit Timer is more fitting for intervals and Tabata training than longer circuits. Cost: $0.99, compatible with all iOS devices.

A HIIT Interval Timer. This no frills app is a simple way to time all those interval runs without fumbling with the buttons on a treadmill. Set custom workouts and follow the color-coded interface to know how many sets are left till it’s time to hit the showers. Cost: $1.99, compatible with iPhone and iPad.

HIIT Workout Timer. For a slightly busier (and cheaper!) app, Workout Timer has customizable options for beginner, intermediate, and advanced workouts, low and high intensity intervals, and of course — time for rest. Cost: $0.99, compatible with all iOS devices.

Seconds. Any app that includes “time wizards” is a winner with us. Customize infinite workout timers, assign music for specific intervals, and share your workout with other Seconds users. The sexy, easy-to-use interface might even help people want to run intervals every day. Cost: $4.99, compatible with iPhone and iPod touch.

Interval Run. Want a virtual coach in your ear buds? Then try out this app that tells users when to start running and when to (finally) take a breather. In addition to Tabata workouts, the app let’s users customize longer running workouts, from 5K plans to hour-long runs. Cost: $1.99, compatible with iPhone and iPod touch.

iSmooth Run. What’s cool about this app is users can plug in the pace and heart rate zone they want to achieve during each interval. The simple interface will make any workout, well, run smoothly. Cost: $4.99, compatible with iPhone.

Tabata Training Apps

Photo: Tabata Pro for iOS

Tabata Pro. Twenty seconds on, 10 seconds off. Simple enough, right? While this app won’t make those squats burn any less, it’ll take users’ minds off of worrying about timing a Tabata. Just set the number of cycles and hit start, and you’re good to go! Cost: $2.99, compatible with all iOS devices.

Tabata Trainer. What’s great about this Tabata app is that it comes preloaded with nine full Tabata routines, along with a customizable option to create your own. It’s sleek and simple too, and you can share your workouts on Facebook for a tech-savvy humblebrag. Cost: $1.99, compatible with all iOS devices.

Do you use any apps for interval training? Did we miss any? Share your picks and experiences in the comments below!