The word Fartlek always makes me laugh.
Fartlek, which means speed play in Swedish, is a training method that blends continuous training with interval training. Fartlek runs are a very simple form of a long distance run.
Fartlek training is simply defined as periods of fast running intermixed with periods of slower running. Any length and amount and does not have to be structured.
A good way to do it if you have never done this type of training before is to use lamp posts or tree lines and decide on whether you are going to run fast for two and jog for one or fast for four and jog for three, whatever you want.
The best way of getting your fitness up is to have short recovery sections and work hard on the fast runs.
You can also do by time and make up your session before you start or adjust during the session.
I love this type of training. It’s almost like a HIIT session.