This pair of articles gives a simple introduction to aerobic interval training. The 'Practical Aerobic Intervals' give advice on how to start doing aerobic intervals. The '101' article gives a little more background. These are not intended to be comprehensive guides, but rather a starting point. As always, I would highly recommend reading "Jack Daniel's Running Formula."
http://fellrnr.info/Practical-Aerobic-Intervals and http://fellrnr.info/Aerobic-Interval-Training-101
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