I thought I’d add my 2 cents.
The old philosophy was to do “cardio” i.e. get your heart rate up for at least 30 minutes 5 days a week. It’s been recently found that that does little for the cardiovascular system. The new wisdom is that you need to do vigorous exercise for maximum benefit.
That is nothing new athletes have been following this method for centuries.
To get maximum benefit from training you need to do a hard work out then allow for recovery. For most athletes that is two days a week of maximum effort with the days in between with light workouts (or off days). For the rest of us the day’s in-between hard days depend on our recovery ability, but 2 days of hard workouts can be done by most. Of course a hard workout is dependant on the person’s ability and shape. A hard work out for me is intervals for half an hour a pro cyclist it would be for several hours.
For cycling a hard workout is a long, hard day in the saddle or interval training.
Bill