Perform exercise 1 for 30 secs, followed by 30 secs rest.  Repeat Exercise 1 for 30 secs, go straight into Exercise 2 for 30 secs followed by 30 secs of rest. Continue this process stacking on Exercises 3, 4, 5 and 6.  The first round is only 30 seconds long (1 exercise) and the sixth and final round is 3 minutes long (all 6 exercises back to back).

Stacking HIIT - 13 mins
1) Prisoner Squat + Oblique Crunch
2) Plank Walk
3) Skaters
4) Mountain Climbers
5) Skydivers
6) Burpees