Interval training is a widely used fitness technique that has generated measurable benefits for many dedicated enthusiasts. While the concept is simple (intermittent bursts of high-intensity work followed by low-intensity work), the resulting workout session is anything but. Apart from a large towel and a CPR kit (you never know!), the most effective tool for interval training is a timer. Any old time keeping device will technically suffice, but given the fast paced nature of interval routines, if you use a typical stop watch, you’re thumbs are likely to develop more of a sweat than your core. Bit Timer ($.99), on the other hand, is a simple, elegant, and easy to use app for one of today’s most widely used gym accessories and time keeping devices: the iPhone.

Its clean user interfaces makes organizing interval workout sessions a breeze. Just customize three simple slots: work period (from 5 seconds to 2 minutes), rest period (from no rest to 2 minutes), and the number of repetitions (up to 40), while the bottom of the screen keeps a countdown of the entire duration of the workout. It’ll also automagically fade songs to warn exercisers about the upcoming change of tempo — making it the next best thing to that aggressive, spandex-encased female personal trainer of your dreams.

Buy Now: $1