What is the best type of Cardio?
First, I think it's important to determine the purpose of "cardio" before selecting an exercise.
I am passionate about running, and while I am certainly aware of the physical benefits, they are secondary to the enjoyment of the experience and my mental well-being.
If one is looking to lose weight, for instance, as many people who say, "I need to do cardio" are trying to do, this is not the best approach (you won't burn enough calories), but one will glean other rewards from it.
Ultimately, the best type of cardio is the one you enjoy doing, so my list is about the one I enjoy.
1. Run up long, steep things.
2. Hike up steeper things.
3. Run down steep things.
This is great for establishing balance, quick decision-making, proprioception, and strengthening the quads.
4. Long, slow running.
Builds endurance, reduces the risk of overtraining, and probably best qualifies as the definition of cardio for most people.
5. Sprint intervals.
Boosts speed and performance.
6. Running in beautiful places.
There is nothing better for the soul.
7. Run stairs.
Also increases strength and mental toughness.
8. Run hill repeats.
Increase strength and mental toughness.
9. Run at altitude.
Boosts red cell count and improves oxygen uptake.
10. Run barefoot.
Improves balance, reduces the risk of injury, and improves running form.
11. For goodness sake, never run on a treadmill.
Besides the fact it's boring, it negatively alters your running form because you're not running on a natural surface (unless you typically find yourself on surfaces that move at a steady pace underneath your feet).