I’ve been throwing this into some of my training sessions and it seems to really add some stress (good thing) to your average cardio sessions.
Carry a medicine ball while walking on an incline.
Take your basic speed for walking at an incline on the treadmill;
Beginners (3.0 mph), Intermediate (3.5 mph), Advanced (4.0 mph)
Set the treadmill to a moderate height (incline setting) which would be some where between level 5 and 10.
Grab a medicine ball between 3kg and 5kg (approx. 6-12lbs) and hold it anyway you want just don’t put it down.
Try that for 25 to 45 minutes depending on your fitness level.
Let me know how it goes!