Check out @mrrobbo 's Continuing List of Great Apps for PE Teachers!
Check out the other top app lists here:
Part 1 http://thepegeek.com/2010/12/07/my-top-8-health-fitness-apps/
Part 2 http://thepegeek.com/2011/03/28/top-8-iphone-apps-for-pe-teachers-part-2/
Part 3 http://thepegeek.com/2011/07/08/top-apps-for-pe-teachers-part-3/
Part 4 http://thepegeek.com/2011/09/19/top-8-apps-for-pe-teachers-part-4/
Part 5 http://thepegeek.com/2011/10/10/top-8-apps-for-pe-teachers-part-5/
Part 6 http://thepegeek.com/2011/11/09/top-apps-for-pe-teachers-part-6/
Part 7 http://thepegeek.com/2011/12/10/top-apps-for-pe-teachers-part-7/
Part 8 http://thepegeek.com/2012/01/19/top-apps-for-pe-teachers-part-8/
or grab the PE Apps app for a great one stop collection of the best PE apps. http://itunes.apple.com/us/app/pe-apps/id474135591?mt=8
This app looks at the rate in which your heart beats; how could this information assist you in working out how to boost your aerobic threshold? Why would this be an effective app in controlling the appropriate BPM for improving this?