Alternating Fartlek: What is it and how do to it!

Today I'm ranting about my favorite time of workout - the fartlek! And more specifically, the alternating fartlek, aka Over/Unders or On/Off workout!

I love these sessions. If i had to pick one type of workout that I could do every week, it would be some variation of an alternating fartlek session. These have been a key to my development as a marathon runner, helping me achieve a 2:16 marathon and stand on 2 Olympic Marathon Trials startlines.