Keeps you cool while doing it, low impact. Many of us love the water and it's a form of exercise that could save your life!
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.
Preferably mountains.
I do no traditional cardio. I am able to remain physically qualified to be a wildland firefighter at kind of an old age just doing the following.
All high intensity means is using enough weight that it forces you to move slowly and very little rest time in between sets. Done correctly, lifting is cardio but traditional cardio will not build muscle mass.
Taken from my own perspective. Not advice.
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