I have tried a variety of interval approaches as part of my efforts to improve both stamina and pace. I have tried short sharp intervals - running as fast as I can for a minute, slower for a minute, repeated multiple times. Today I tried what I think gets called the 1/1 method, i.e. run 1k fairly fast, walk a minute, repeat multiple times (in this morning's case I did 4 sets). I have to say it seemed quite effective. What have others done and what has worked best?