Exercise Isn't About Burning Calories...
It’s very important you understand that the point of exercise isn’t to burn calories.
If you get this wrong you’ll end up making decisions like, “running seems like it burns a lot of calories, it must be the best exercise, I’ll do that”.
Lack of understanding is a big issue in the fitness space because people tend to start training for a specific reason (get fit, get stronger, lose weight, build muscle, escape pain, etc.), yet there’s usually a big gulf between what they NEED to do to achieve their goal and what they ARE doing. Running or HIIT isn’t going to fix your back pain and it isn’t the best route to weight loss either (although it can complement strength training and I wholeheartedly recommend it as part of a rounded programme).
People seem to flock to HIIT workouts and steady state cardio because they think that sort of training will burn more calories. I’m not even going to argue that it doesn’t, because it might, but it doesn’t matter as much as you think.
I think the reason people get attracted to things like HIIT is because of how it makes you feel. It’s HARD and largely unenjoyable, therefore it must be effective, right? Wrong. Although sweating is one (minor) mechanism by which the body rids itself of fat, sweating more absolutely does not equal more fat loss. Perspiration occurs when your body’s internal temperature increases in order to regulate your temperature. That’s it. HIIT makes you hot, so you sweat. And no, heat doesn’t burn fat.
Some will argue that HIIT makes you feel good afterwards, which is fine. If your goal is to feel good after your exercise, then HIIT is a great choice! However, if you want to change your body’s composition and you’re saying “but HIIT makes me feel good” then that doesn’t really add up. This good feeling is actually a reduction in anxiety which, as it turns out, is associated with the body cooling after an exercise induced temperature spike (and it actually seems to be more about the brain heating then cooling rather than the body). This is ‘the Thermogenic Hypothesis of exercise’ if you want to look up more on that. Similar reductions in anxiety have been observed in walking, meditation and simply resting, so the “feel good” could actually be down to a break from daily stressors, rather than 900 star jumps (the Distraction Hypothesis).
Every exercise modality has an intended response and the whole point of the types of exercise that get your heart + breathing rate up (that tend to make you sweat buckets) is to improve cardiovascular function. If that is your goal, do those things, if not, don’t do them. What if you enjoy those things? That’s fine! But set your expectations - you won’t achieve anything other than snazzy lungs. As a side note to that, know that if you run the same distances at the same pace day-in-day-out then nothing will change.
If you want to change your body composition long term, the best thing you can do from an exercise perspective is change your body’s ability to use calories, not just to manipulate your day-to-day exercise-specific calorie expenditure. How? You need to increase your muscle mass.
If you’re untrained (without a long history of weight training) you can do that now, under lockdown conditions, with zero-to-minimal equipment - you don’t need to wait for gyms to reopen. If you need help or advice, please ask.