This link to a PDF is for those training using a heart rate
I have been mostly running at a conversational pace lately and had intended doing so for the entire duration of our 7 week stay in the USA. I dont really need a HRM to do this except that it is good for long runs as HR tends to creep up too high over longer times and the monitor allows me to keep it down. However where we are currently staying means a long 2 mile uphill in any run that I do and it has been impossible (well - maybe not impossible but certainly not enjoyable) to keep HR down up a 2 mile long hill so I started to investigate possible alteratives to insert into my easy runs to get me up this hill.
Coach Roy Benson talks about "fartlek intervals" in the above book so I have been doing them. Starting off with 15 minutes of easy running (downhill), I have then been doing up to 30 minutes of fartlek whereby I run faster until my HR reaches 90% of HRMAX and then walk until HR returns down to 70%, then rinse and repeat. Depending on the hill gradient at any place, I run sometimes much faster than normal or simply a little faster than normal until my HR reaches 90%. It has made getting up the long hill more "interesting"and enjoyable - plus I can feel it doing me good!!😃