Hadd wrote:
Okay, I got it. You want a more general discussion; like is there some training effect to be gained from singles that cannot be gained from doubles, or vice-versa?
Well, the simple answer is, that depends on who (or rather what type of runner) is doing the training. But that don't help you much.
Lemme give you a fer'instance:
In more ways than one, the greatest thing that ever happened to me was meeting Mrs H. It was probably Ed Coyle (if memory serves me right) who stated that what kind of performance level you were gonna ultimately achieve basically came down to just two things (I'm paraphrasing): years spent training and percent ST fibres.
Mrs H has the latter in spades. Way more than I who am the much more common, more-FT kinda guy. So when it came to talent, she was forever way more talented than me.
For many years we ran every session together. So, she talked me into doing track work early morning at 7am rather than 6pm in the evening. Track's quieter, it's cooler ... she had some good reasons.
The sessions mighta been 1k or 1200m reps at a shade quicker than 5k pace, or 5x2k at near 10k pace, or even 3x3k...
It didn't take long for me to learn that I HATED those morning sessions. Hated them with a passion! When we did them in the evening I found them WAY more comfortable or at least more do-able. Mrs H was happy as a bird; AM or PM meant nothing to her.
It didn't take long for me to figure WHY I hated them, and once when she was giving me the, "hey, what's up with you?" look, I explained it to her.
I'm an FT-guy, that means I burn way more sugar than she does, at ANY pace. Hell, at EVERY pace. Falling outta bed first thing in the morning, I was basically trying to run hard WITH NO SUGAR! My liver glycogen was low after keeping me warm and my organs ticking over all night. My blood sugar was low since there was no glucose coming from the liver to keep it up... and here I was trying to run hard. Wasn't gonna happen, or at least, not in a way that would improve me.
At high intensity my FT muscles need to suck every last bit of glucose outta my blood to keep me shifting. I'm burning a huge level of glucose/glycogen to fuel my pace compared to Mrs H who is much more fuel-economical and needs way less than me (not least because she only weighed 90lbs).
At all paces my BLa was higher than hers (we tested) showing that I was burning a greater percent of sugar than she was at the same pace (which is the inherent difference of FT vs ST).
To drive my muscles hard, my brain needed sugar from my blood ... and first thing in the morning it wasn't getting any. I never found anything so mentally and physically draining (on me) than those hard-ass morning track sessions. By the end of the last 2k rep, I was ready to kill three people! Any three! To offset it, I found myself getting up extra early and trying to boost my blood sugar before going to the track, and not always successfully.
So (long story short): morning runs for FT-types, better be easy running. We had a regular 10-miler some mornings when Mrs H was >100mpw and I was even >130mpw. Maybe steady is okay (quickest maybe M+30), but definitely not fast, we FTs burn too much sugar and haven't taken enough onboard yet; by afternoon liver and blood sugar are up and it's better and we can run the same session much easier. ST's, it don't seem to make much of a difference.
Let's step back a bit: what does training do to muscles anyway? At the simplest level we are trying to recruit a number of muscle fibres and use them till we exhaust them of fuel (glycogen and fat) and then recruit others to replace them until they too are fuel-exhausted. And so on.
We run far enough, it is possible to run out of glycogen to such an extent that we can no longer continue at the same pace (we see this in marathons as runners hit the Wall). There is no need to go to such extremes on a regular basis (daily), but essentially that's what we are trying to do; exhaust enough fibres so that this stimulates adaptation: storing of more muscle glycogen within the cell for next time, stimulating increase of aerobic enzymes so we can break down more fuel quicker next time, growth of mitochondria for greater oxidative capacity ...
We could run one mile every day, and there would be some improvement in terms of fitness, but I think most people can see that you would not get to recruit enough fibres in such a short space of time to provoke serious change.
We could try running faster for that one mile. The faster we run the more fibres we'd recruit ... but then the type of adaptations would also change; we run too fast and we'd never improve our ability to burn fat as a source of fuel, for example. We'd never become maximally economical on such minimal mileage; nobody'd suggest one mile a day as a marathon-training schedule.
We could run uphill. Because we'd require more power, that'd recruit more fibres than on the flat ... but again, the type of adaptations would alter.
Those tend to be the major options for fibre recruitement (although there are others): Run long enough or often enough. Run quicker. Run uphill.
If we take the first; Run long enough or often enough, this is essentially the singles or doubles argument.
Singles (eg: like the marathon example above) are shown to exhaust all your fibres if you go far enough. Therefore, singles have to be long-ish. Singles and short runs don't cut it. Long singles and you get 24hrs to replace enough muscle glycogen to go again the next day. If you go far enough, you will not replace muscle glycogen in ALL the fibres you exhausted to be able to run that far again the next day (few people can replace fuel well enough to run marathons back-to-back-to-back... but don't ever think it's beyond the ability of serious-ST's; they're a breed apart).
Doubles, and you get the chance to refuel after the morning run and go again that evening. Doubles tend to be shorter than singles (you have to be able to go again in a shorter length of time). In the 8-12 hours between runs, do you refuel a major part of the fibres you used that morning and thus recruit them again in the evening? That is very possible, and one reason why doubles mustn't be too short. Yesterday I replied to one young guy on here who runs a 6k loop AM and PM on a regular basis. Is it not possible that he is simply exhausting and refuelling many of the same fibres (or a large percentage of the same fibres) twice per day? Doubles won't help him much if that's what he's doing. He's leaving way too many fibres unrecruited.
You don't recruit a fibre, you don't stimulate it to change/adapt/improve. So the question really becomes, what training regime will allow me to reach as many fibres as possible on a regular basis?
ST's are so fuel-economical they need more mileage than FT's to exhaust their fibres: their MPG (miles per gallon) is higher. FT's burn a higher percent of glycogen than ST's so don't have to go as far in order to exhaust their fibres. ST's often don't know what the Wall is; EVERY FT knows what the Wall is.
The advice I gave to Joe, suited Joe. He is an ST and mileage means little. That schedule would not have suited a more-FT type of runner who would have "bonked" on low glycogen often on such a regular schedule of lengthy singles. An FT would not have refuelled in enough time each day. So doubles might suit an FT more (gives him more regular refuelling time).
Note also that FT's need to run easier than ST's (our BLa is higher than an ST at equivalent pace). See on the Cabral&Hadd thread that Mamede would run his easy runs much more slowly than Lopes, despite their 10k PRs being very similar. In many ways they were ideal archetypes of the ST vs FT dichotomy.
This was a good question, and I have not resolved it by any means. Just talked aloud. I may come back to this.
I would go back to what I said at the beginning; when you ask the singles or doubles question, that depends on who (or rather what type of runner) is doing the training.