Rock climbers have known this for a while. Climbing long sustained routes builds endurance, but not strength. Short strenuous bouldering problems build both endurance and strength.

Personally I think climbing is the perfect hacker sport. Climbing nearly always favors forethought and elegance over brute force. Bouldering problems are so named because they ideally require several iterations to find the optimal path. Sometime a single moment of insight is all it takes for a problem to go from very hard to trivial (in the hacker sense of the word); yet there is always something new to learn, even from trivial problems.

Well it worked for rats. And looks pretty good for youth. But there need to be caveats.

?How many in middle age will respond to "a few minutes of intense exercise to point of pain" with heart attack?

?What about mental health? Research findings in recent decades suggest something more sustained is needed for the endorphin boost that fights depression.

Every day, I bike from downtown SF (work) to the top of Russian Hill (home) on a fixed gear bike (~1 mile, ~500ft elevation gain).

About once every month or two, I bike 50-150 miles in a day, and don't find it problematic.