I don’t consistently have time for 4 hour rides during the week days, but I can do two 2 hour rides, both before and after work. I figure 2x2hr is going to give me twice the training stress and adaptation of a 1x2hr, but how does 2x2hr compare to 1x4hr? I’m still going to do long rides twice a week, so big rides are still in play, I’m just curious how splitting up the days workout ends up adaptation wise. The reality is I don’t have any other option, but I’m curious on what to expect.
My understanding is that there are specific adaptations that are targeted after about 90 minutes of activity. Any significant break will allow your muscles to recover. I’m not sure if there is research on how long you can break and maintain that target adaptation.
That being said, 2x2 hours is infinitely better than 0 x 4 hours 
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Some researchers have proposed that on long rides your body starts forcing fast twitch fibers to work aerobically, which could be a benefit of doing the 1x4 instead of the 2x2. But I’m not sure if this has actually been proven yet and it’s definitely not something to worry about, you will still drive adaptations increasing volume regardless. Another benefit of longer rides is testing out nutrition strategies and identifying potential issues with your bike fit that might not show up on a 2 hour ride.
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That’s exactly where I’m at with it. More volume should give more training stress than less volume, so it should lead to more potential adaptations. I guess I will find out.
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Not true.
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This has been known since the 1970s. However, you don’t have to ride that long before you start recruiting type II motor units (and, of course, you can also recruit them by increasing the intensity).
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Two-a-days are quite common in other endurance sports - I don’t know why so few cyclists (other than trackies) seem to regularly train this way. Coming from running, though, I did this quite often.
As for what’s better/more effective, I don’t think it matters. If the intensity is exactly the same, the 2nd 2 h of a 4 h ride might provide a greater stimulus than a 2nd 2 h ride, but splitting the session in two should allow you to train harder, which should make up for it (and possibly more).
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Admittedly “specific adaptations targeted” was a poor choice of words, but aren’t there physiological adaptations that are more pronounced after about 90 minutes of endurance exercise?
The opposite, actually, at least based on studies of rats (can’t readily study this question in humans).
That is, the effects of training on the most important muscular adaptation to endurance exercise, I e., mitochondrial biogenesis, apparently saturate after only 1-1.5 h of exercise:
Note that the increase in cytochrome c content in this case is similar to that found in Holloszy’s classic studies, in which rats were run 2 h/d.
The only other study of voluntary exercise of which I am aware that tried to push things further is one by Howie Green. They set out to have rats doing two-a-days using the Holloszy protocol (8 min steady-hard, 2 min sprint, repeat 12 times), but the rats couldn’t handle it. The best they were able to work up to was 2 h in the morning and 1.5 h in the afternoon. The study was done in conjunction with Dirk Pette (I think Green did his post-doc with him), so of course in the Introduction they compare their results to chronic electrical stimulation (Pette’s speciality), and conclude that have matched the increase, thus topping previous studies of voluntary exercise. If you actually go by the data, though, they didn’t, i.e., the improvements were similar in magnitude to the previous studies mentioned above. Instead, what seems to happen when you keep hammering on the muscle is that you reach a point where you can no longer continue to increase the capacity to supply ATP aerobically, so what happens is that you reduce ATP demand, by replacing fast myosin with slow myosin.
Another way to approach the question from the human side is to ask, what’s the least amount of exercise per day needed to roughly double mitochondrial respiratory capacity, which is the magnitude of the increase found in rats and also when comparing highly endurance trained athletes to untrained individuals? The answer is, as little as 40 min/d, at least if the intensity is high enough.
Empirically, I think that everyone would agree that you need to train a lot to reach the limits of your abilities. However, from a scientific perspective it is difficult to justify training more than a couple of hours per day, at least based on muscular metabolic adaptations.
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This screams double threshold https://www.mariusbakken.com/the-norwegian-model.html
Just kidding, while it seems to provide excellent results, I couldn’t torture myself like that.
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Maybe it’s just bro science, but why would the best endurance athletes in the world ride for more than 40 minutes at a time if it wasn’t providing significant benefit? There’s got to be better evidence than a rat study done in 1980.
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Its in the last paragraph, important bit quoted…
I.e its not the whole story.
It’s not as torturous as it sounds. “Threshold” in this model is at a reduce intensity - more like tempo or sweet spot in cycling lingo. That allows them to achieve a high volume of higher intensity subthreshold work.
Going for the last 5% of benefit? They also do 5-6-7 hour races so they need to simulate the saddle time in their training.
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It’s their job. They aren’t time crunched. At/near their genetic potential. Marginal gains, etc etc. If they need to get in X stimulus/TSS, why would they break up their workouts into small chunks? They can put in big loads then recover the rest of the time generally without other responsibilities such as work, family and chores. Us common folk need to fit in training around our lives, so splitting up workouts makes more sense.
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So this has me thinking about threshold training, and increasing time duration. Taking a logical leap would you say that if my TTE was 60min. Training 2x20 two days in a row… or AM/PM would be the same as 4x20 in the same session.
It also will depend on type of event you’re targeting. You should get your body used to eating/drinking/fueling for long periods of time. You should also get your body used to expending energy for long periods of time - I definitely perform differently after burning 2000kJ+ than I do after burning 1000kJ. There’s lots at play, but that does not mean you won’t get many benefits out of a 2x2hr ride. There are likely benefits in a 2x2hr ride that you wouldn’t otherwise get out of a 1x4hr ride.
Isn’t glygocen depletion one signal for endurance adaptations? Long rides definitely do that. Dylan Johnson had a video about double days if I remember right.
Possibly, but 1) it’s not yet entirely clear, 2) even if it is, A) other factors (e.g., Ca2+ release) are obviously more important, and B) “going long” isn’t the only way of reducing glycogen levels.
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Hard to say, but I don’t put much faith in estimates of TTE.
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To which one might add, nobody can go that hard on a daily basis for the duration of their career…unless you’re a swimmer or a rower, in which case life revolves around intervals in a team setting, not coffee shop rides in the mountains with your 'mates.
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