Cardio Intervals - Pick one of the following
Row 5 x 500m 2 mins Rest between each Row
Run 5 x 400m - 2 mins Rest between each Run
5 x 60 Box Steps 16"20" - 2 mins Rest between each
5 x 2 mins Air Dyne - 2 mins Rest between
This has a 1 to 1 work rest ratio. So work as hard as you can on each set.
5 by 400m runs with 2 mins rest between, tot time 19:58