This is the first in a series of articles on interval training. Over the years I have come to believe that interval training should be used by all runners of all abilities. To plagiarize Sun Tzu and add a little hyperbole, "It is a matter of life and death, a road either to safety or to ruin. Hence it is a subject of inquiry which can on no account be neglected."
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P.S. If you've not read Sun Tzu, you really should. It's not just about war, but about how to succeed, regardless of how you define success.