Interval training, wherein a person engages in physical activity at alternating levels of intensity, is typically used by competitive athletes looking to build strength, speed and endurance. The ITGO - Interval Trainer Go iPhone app, which is a precise timing tool, is clearly geared toward that type of athlete.
On first glance, I found the app a bit confusing, because it is composed of dial upon dial, and ticker within ticker.
The top dial, however, allows you to set the total length of your desired workout. The second dial allows you to set the length of your intervals in seconds. And the third dial is where you set the ratio of high- intensity activity to low-intensity activity.
Once you have established your centers, jump to the timer. In the center of the timer is a digital clock which tracks how far along you are in the entire workout. The inner ticker is the high intensity workout, and the outer ticker is the low intensity workout.
So if you are running, for example, you sprint while the ticker makes it around the inner circle, and jog while the ticker traces the outer circle. A rather obnoxious male voice commands you to switch from "fast" to "slow" (this can be switched off).
The app does allow you to create "fast" and "slow" playlists, but it is nothing different that what you can do within the iPod on your iPhone.