The challenge incorporates all kinds of lunges, and there’s no need to stick with just one modification. If you’re advanced/fitter, adding plyometrics to your lunges can give you faster results and a higher burn than the basic lunge can.
Try this modification using just body weight at first. When you’ve got it down, try adding a medicine ball or holding a dumbbell to add difficulty. Beginners: go slow and break it up into 2 movements: 1 lunge, stand, 1 jump, stand.
Challenge: 100 of these today (50 per leg). 5 rounds of 10 or 2 rounds of 25.