4 sets
Set 1 15 Leg extensions with 1 second hold at the top of full extension each rep, immediately follow with 15 leg curls with 3 second slow count on descend.
Set 2 12 heavier Leg extensions with 1 second hold at the top of full extension and 2 second slow count on descend each rep, immediately follow with 12 leg curls with 3 second slow count on descend.
Set 3 12 Leg extensions with 1 second hold at the top of full extension and 2 second slow count on descend each rep, immediately follow with 12 leg curls with 3 second slow count on descend.
Set 4 10 heavier Leg extensions with 1 second hold at the top of full extension and 2 second slow count on descend each rep, immediately follow with 12 leg curls with 3 second slow count on descend.

Note: Increase weight each set. Get heavy on the leg curls! For the leg extension set up, grab a chair with a back and place some books or anything that can safely raise you, your feet and dumbbell should be off the ground in order to have full range of motion. Make sure to have a chair with a back or use a wall! Get creative but stay safe. Rest 90 seconds between sets.