By Laura Schwecherl

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 fitness. 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.

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  • 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 <a href="http://vova.galchenko.com/iphone/circuit_timer/" target="_hplink">Circuit Training Timer</a> let them know when it's time to stop n' go. <em>Cost: $0.99, compatible with all iOS devices.</em>

  • Intervals

    From squat to sprints, users can easily <a href="http://intervalsapp.com/" target="_hplink">customize intervals and circuits</a> for the perfect heart-pumping workout. Features include various audio settings, warm up and cool down options and a CrossFit WOD timer. <em>Cost: $2.99, compatible with iPhone and iPod Touch.</em>

  • Bit Timer

    Probably the sleekest application of the bunch, <a href="http://www.bittimerapp.com/" target="_hplink">Bit Timer</a> 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. <em>Cost: $0.99, compatible with all iOS devices.</em>

  • A HIIT Interval Timer

    This <a href="http://itunes.apple.com/app/hiit-timer-intervals/id309423464" target="_hplink">no frills app</a> 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. <em>Cost: $1.99, compatible with iPhone and iPad.</em>

  • HIIT Workout Timer

    For a slightly busier (and cheaper!) app, <a href="http://www.knila.com/hiitpaid.aspx" target="_hplink">Workout Timer</a> has customizable options for beginner, intermediate, and advanced workouts, low and high intensity intervals, and of course -- time for rest. <em>Cost: $0.99, compatible with all iOS devices.</em>

  • 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 <a href="http://www.secondsapp.com/" target="_hplink">Seconds</a> users. The sexy, easy-to-use interface might even help people want to run intervals every day. <em>Cost: $4.99, compatible with iPhone and iPod touch.</em>

  • Interval Run

    Want a virtual coach in your ear buds? Then try out <a href="http://deltavee.fi/wordpress/interval-run/" target="_hplink">this app</a> 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. <em>Cost: $1.99, compatible with iPhone and iPod touch.</em>

  • iSmooth Run

    What's cool about <a href="http://www.ismoothrun.com/" target="_hplink">this app</a> 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. <em>Cost: $4.99, compatible with iPhone.</em>

  • Tabata Pro

    Twenty seconds on, 10 seconds off. Simple enough, right? While <a href="http://www.simpletouchsoftware.com/products/tabatapro/" target="_hplink">this app</a> 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! <em>Cost: $2.99, compatible with all iOS devices.</em>

  • Tabata Trainer

    What's great about <a href="http://www.tabatatrainerapp.com/" target="_hplink">this Tabata app</a> 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. <em>Cost: $1.99, compatible with all iOS devices.</em>

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

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