Can anyone point me to some literature, post, or something that shows how long a Z2 ride should be before you see any benefit? I have a triathlon buddy that wants to do Z2, but only has 1 hour chunks commuting to and from work. I told him to check whether Z2 with that little time (2 hours, but 2-a-day) makes sense. My gut feeling (not based on anything other than what I believe I've heard) is that Z2 for 2 hours a day is not worth it, and certainly not if broken up into 1 hour chunks separated by the work day. I told him to SST during his commute and save the Z2 stuff for long weekend rides. Good advice?