Some cyclists ride slowly, others ride hard. This study of bike commuters in Denmark says that riding harder (higher perceived effort and intensity, pushing hard enough to feel "breathless") gives the most health benefits (measured by mortality rate). How hard you ride has far more effect than how long you ride, the study concludes.
I think I've read other articles saying that brief but "high intensity" exercise improves heart health, perhaps more than longer periods of lower intensity exercise.
What do you think? I imagine that most of us go for longish rides - a few hours, 30 to 50 miles - at an effort level that isn't anywhere near our maximum - otherwise we couldn't sustain it for hours on end. How about going out, repeating 30 second all-out sprints followed by a couple minutes of recovery, and wrapping it up in ten minutes? Anyone do that? Lack of time or poor weather would no longer be an obstacle, hmm.