Some people consider cardio just a mere way to burn more calories, others swear by it and find it essential to maintain a certain body shape, some avoid it completely scared to lose muscle, others just do it when trying to lose weight.
I always recommend to include cardio into a training program, just like weights, but regulate intensity, duration and frequency depending on your body type, training level and goal you have in mind.
Personally I find cardio very effective when the goal is losing fat. These are the main reasons:
Lift mood, motivation
And of course mobilize stored fat.
First thing in the morning on empty stomach, about an hour, first 30 min of intervals, that’s how I prefer my cardio. But there are lots of ways to do it and what really matters it’s not much the time of the day, more when you can give your best in terms of performance and energy levels.
But what about GOALS and periodization? Like you rotate your weight training, your diet, so you should do with your cardio.
To benefit from it, as rule of thumb I’d suggest to keep at least 1-2 sessions of HIIT a week (sprints, intervals, tabata etc), the remaining sessions being medium intensity and another one for recovery if you wish.
If you are trying to gain muscle, I’d lower duration and frequency (shorter sessions about 30-40 min, 3 a week for example). To lose fat, raise duration and frequency (sessions up to 1 hour, even 6 a week, double am + pm if needed on few days).
What I wouldn’t do is TONS of cardio regularly, unless you really have a lot of fat to lose or your training program requires it (training for marathons, for example). I rather have fewer sessions of great performance and intensity, rather than everyday mediocre ones. Cardio is toxic on your joints and put your body into a catabolic state easily, if not done properly. So you gotta learn how much cardio is good for you and your goals.
In the end cardio is a great tool to burn calories, improve endurance and anaerobic capacity, boost metabolism and of course strengthen the heart muscle. With diet and weights, constitute the perfect equation for a well trained, lean body. Just remember like weights, more is NOT better.