Originally Posted by
trisaiah
I agree with several posters who have said we need to see some evidence for this. Not because I am claiming you don't know what you're talking about necessarily, but, quite frankly -- I don't know what you're talking about.
First of all, you need to explain what you mean about "aerobic benefit." The word "aerobic" describes the way your muscles are working, not a type of fitness gain. When I see "aerobic benefit," I think "greater capacity to perform aerobically" which includes a huge array of physiological changes.
Now, if two relatively novice cyclists jump on a trainer and one bikes for 50 minutes and the other for two hours, I AGREE that the second sees hugely diminishing (even negative) returns for exercise more than 30-50 minutes in terms of oxygen uptake and muscle growth. In fact, the second biker's leg muscles will go very strongly catabolic after about 3/4 of an hour.
But what about, say, the ability to burn fat preferentially over glycogen stores? Even a novice biker going for 2 hours twice a week is going to be VASTLY more efficient at conserving glycogen then the biker doing 1 hour sessions, after just a few weeks. I think that cardiovascular efficiency (I mean the ability to maintain the training-level-specific power output over a given duration at a lower heart rate) probably sees a substantial improvement as well.
All of this explains to the OP why it's best off to mix duration as well as intensity. Long bike rides have substantial benefits, but maximum overall fitness is achieved with training in multiple intensity zones.
To clarify: So far this winter, I'm riding an average of 6.5 hrs./week, spending 1 hour at or above LT and one hour in zone 3, with many short, very hard efforts. So 4.5 hrs in zone 2 or below. This training mix allows me to mix it up with my riding buds. I can ride a century on any given day. That's what I'm talking about. I could increase to 8 hours/week of zone 2 and not get much additional benefit for this time of year. That's more or less my summer schedule. A few percent - might drop my climbing time by 1 minute/1000'. Increasing zone 2 time does increase endurance, allowing all day, multi-pass rides, but that's not important to me in winter, and probably not important to the OP at this time. OTOH, I could ride 8 hours/week in zone 2, leaving out the work in zones 3 & 4, and do very considerably worse. I agree that at least one 3-4 hour ride/week is critical, year-round.
So I'm arguing that the fetish for only riding in zone 2 for base building is a lot of time-wasting. It may make sense if you earn your living by riding and need every fraction of a percent. Or maybe not even then. I don't believe there's any research to show that only-zone-2 riding has any benefits at all. There is research showing that increasing total weekly riding time from 10 to 20 hours results in gains of only 2-3%, but I can't find it at the moment.