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Unless you have a treadmill or similar at home to dust off and use, track or trail running is a free alternative for endurance exercise. I always advise against true road-running unless you have no history or family history of lower joint issues.
As we have oft repeated, endurance exercise is worth doing once weekly if you do two other days of calisthenics (which also have endurance components). Although many refer to running as "cardio," it does little or nothing for heart functioning unless it includes HIIT, such as sprints.
Related, 10,000 steps: Not quite magical when it comes to weight. Walking is great to maintain mobility especially in the elderly, but it does nothing for the heart and certainly nothing for losing fat. Quite enjoyable, though. Walks are great, with friends, spouse, whatever.
"Although many refer to running as "cardio," it does little or nothing for heart functioning unless it includes HIIT, such as sprints."
So that would mean it must be true for treadmills and the like and any steady state cardio. I think you might be referring to joggers who never raise their heart rates to level to elicit a training response.
I've put more miles on my beloved Bianchi road bike (aluminum alloy frame, Campagnolo Daytona gruppo) in the last three weeks than I had in the previous five years! I'm working at home full time so no time wasted commuting, the weather is perfect here in AZ, and the road traffic is very light, making me feel much safer (most of my biking has been off-road because of the traffic).
I started with a 10-mile ride, then up to 15, will probably do 20 today, with an overall average speed of about 15mph. I push myself pretty hard (well, feels hard to me anyway) during the rides (my Apple watch says I burned 744 active, 874 total calories with an average heart rate of 144BPM during my last ride) but will probably start adding sprint intervals soon.
If you are truly "running" (for whatever that means for you); its easier than any other exercise I've ever done to get your heart rate up over 85% of max and hold it there for a while. I think that does your heart a lot of good.
I'm not saying you should do any HIIT, but if you really work at it you can't do true HIIT more than 2 or 3 times a week. So, if you just run steady on other days that's fine.
As I've said several times on this site before, the best exercise program is the one you'll actually do, consistently, over time. If that's running, fine. If something else, that's fine too. JUST DO IT!
I’m sorry but this is just false: “running ... does little or nothing for heart functioning unless it includes HIIT, such as sprints“.
Take a person who does nothing for exercise and have them walk a mile a day for two weeks, then 2, then walk/jog a mile every other day for 2 weeks, then 2. Then two days on, one day off. Etc. Eventually after 3-4 months you get to running 3-4 miles a day at 8 min per mile or faster. 20-25 miles a week is the magic barrier for becoming a “real runner”. Not a jogger.
That persons heart is in measurably better condition than when they started, along with all the other benefits like vastly improved lung capacity and efficiency, new capillaries improving blood flow to muscles and skin - runners always have amazing skin - improved blood chemistry and more red blood cells to carry more oxygen throughout the entire body, and tons of other benefits. The list is long.
None of this is news, it was all demonstrated in the book “Aerobics” by Dr Ken Cooper in the late 60s, who did extensive studies on the value of aerobic exercise. Surely you’ve heard of it.
I’ve also lived it in my own life, as has every other person who ever took up running seriously.
So if your position is that Cooper’s research was b.s., then demonstrate that. And until then, please stop offering this terrible advice.
Trail running is much more dangerous for your body than road running. Much higher risk of a trip or slip, or just having your body move the wrong way and tearing something.
Distance running is also much better for cardio than HITT, as some other commenters have pointed out. You also don't have to run that fast, any running including "slow jogging" helps improve your cardiovascular function and overall fitness appreciably, as advocated by the late Professor Hiroaki Tanaka. https://www.youtube.com/watch?v=9L2b2khySLE This form of running is very popular in Japan and is less stressful on the body and joints.
Step aerobics is a very effective alternative when you can't get outside. And the equipment is cheaper and more compact than an elliptical or treadmill. Doesn't require electricity either. I easily reach max heart rate for my age (50+) without using all the spacers that came with the step. I switch it up with hand and ankle weights, or dumbells.