I find that doing arm swings and such movements are great for opening up the muscles for more endurance. Running with a medicine ball makes running easier to do. It's easy to extend running time by lowering one's speed, so your system is not straining too hard. Mixing up different endurance workouts also helps, too because using one workout too much will cause disproportionate development.

However, be very careful with doing long cardio sessions, because it can actually lower your testosterone which can lead to health problems. It's better to cap off your endurance work to ten minutes a day-ish, and use a degree of resistance to protect your t-levels.

I like the Conecpt2 rowing machine Lends itself well to endurance training without pounding your joints.

I would look for videos or classes that include burpees and mountain climbers...they really do burn a lot of calories and increase your endurance while strengthen the lower body as well. The other thing I like about these is that you can easily measure your progress in a few different ways: the number of repeats and/or your form. You can adapt both to your own physical ability, flexibility level, etc. Progress on your own.If you do these 2-3 times a week, you will be very surprised how quickly your stamina and agility increases. I also have a few other variations that I use, doing each routine for about 6-8 weeks.Let us know what you decided on...and how you are doing!