You can increase the challenge of the workouts in a few ways:
- Choose heavier weights. If the workouts feel too easy, then challenge yourself by lifting heavier.
- Decrease your rest time. Rest for 30s or less between exercises, instead of for 60s or more.
- Wear a weighted vest during bodyweight exercises. If bodyweight push-ups are easy for you, then add resistance by wearing a 10-50lb weighted vest. This will definitely increase the intensity of your workout!
- Increase the speed of your sprint intervals. You should feel like you're approaching "breathless" during your intervals.