As mentioned by the brothers above, push-ups, pull-ups, jumping rope will all get the job done. Most treadmills fold up making storage easier. When I am away on travel, I carry a jump rope, resistance bands, and utilize the good old push-up. I will jump rope for 15 min, then immediately drop and do push-ups to complete failure. You will find a way to get to that target heart rate if you want it bad enough, come back and fill us in on what works for you.