Interval Challenge

Before proceeding, you must be at an intermediate to advanced fitness level to do this safely. As a guideline, if you can run a 10 to 12 minute mile, this is a great workout to do on your non-running days. If you aren't at that level, do not try this workout as it must be done over a 15-minute period with little to no rest (less than 20 seconds of rest between exercises).