Complete as many reps as possible in 20 seconds followed by 10 seconds rest, alternating exercises, repeated for 8 sets of each (16 sets in total). Complete with a continuously running timer from start to finish.

• Mountain Climbers
• Sit Ups

Scaling Down. 

Sit up only as high as you can go comfortably. even if it's only a small movement. 

Technique Tip! 

Try to drive the knees between the arms when doing mountain climbers. Think of an imaginary line drawn between your thumbs as the target for your knees to pass over then return to a fully extended position (straight leg).