This is the correct use of treadmills. Increase the intensity to increase the burn. Do not waste your time by spending 30 minutes on any indoor cardio machines at low intensity. If you are going to do it then might as well do it right. For purposes of getting lean, loosing fat, weight loss and maintaining strength here is the right workout for you.
Dynamic Warm-up
Then:
5 rounds
60seconds x Treadmill Speed: 12.5mph Incline: Grade 15% +
20x Mountain Climbers +
20 Press-ups +
60 seconds Rest
Then:
4 rounds
30 seconds x Treadmills Speed: 14mph Incline: Grade 15% +
10x Pull-ups or Inverted Rows +
10x DB Shoulder Press +
60 seconds Rest
Then:
3 rounds
15 seconds x Treadmills Speed: 15mph Incline: Grade 15% +
10x Curls +
10x Halos
30/60 seconds Rest
Then:
Cool down and Stretch