There's not much evidence for that, and some evidence that heart health is improved by sustained submaximal exercise. In my experience the best improvements I h

There's not much evidence for that, and some evidence that heart health is improved by sustained submaximal exercise. In my experience the best improvements I have sustained in overall fitness have been from either very short, very brutal exercise (NOT just splitting up a dose of 30 minutes into easy sections) or from chilling out for 40-60 minutes at comparatively easy pace. The latter has been something that you can do all the time; the harsh interval training is something that seems to work in 2-3 week bursts with time off afterwards. Anything is a lot better than nothing, but there is some evidence that there are all sorts of good effects from a longer session once in a while. The other thing about phasing in short brutal intervals for a few weeks and mostly doing Long Slow Distance ("LSD") is that it's either over quickly or it's quite pleasant. I get most of the exercise in the more painful 'middle' of this continuum from sport. EDIT: here's the article that got me interested in LSD style training. https://www.elitefts.com/education/training/echocardiography-evidence-of-cardiac-output-training/ https://www.elitefts.com/education/training/echocardiography...