Singles vs. Doubles:
Part 1- Introduction
Part 2- Evidence for doubling: training in glycogen depleted state
Part 3-Revisiting Single vs. Doubles: Evidence from Dathan Ritzenhein

I’ve been dabbling around with this idea in my head for quiet some time. I’ve even mentioned it on this blog before. The question is how long should easy days be and can they be split into relatively short runs?

It’s common sense to think that one 8mi run is better than two 4mi runs, and that definately holds true when building general endurance. During a period of time when the focus is on general aerobic base building, it makes sense that you want that longer stimulus.

However, when it comes time to start doing harder work and ultimately during racing season, is it better to do one 8-10mi or two 4-5mi during an easy day?

I really have no idea what the answer is. So feel free to write in with thoughts, comments, critiques. I’m going to do a little bit of thinking out loud to try and see if I can wrap my head around this issue.

The initial reason that I’ve kicked this idea around so much is my own training in HS. Due to circumstances at my HS, we trained twice a day and generally split our mileage right down the middle. Why did we do this? First off, we had CC first period, so running in the morning made sense. We also had afterschool practice, so once again it made sense to run again. Secondly, and perhaps most importantly, we were restricted to running on our campus. So, we had a 1.5mi loop that I ran way too many times. No one wanted to run 8mi straight doing loops, it was mind numbing to do that every day. Lastly, it’s just how things had been done traditionally. Starting out, we weren’t running that much mileage so a couple loops in the morning and afternoon was all that was done.

If I go back and look at my logs, in 2002 I mostly ran 4.5 and 4.5. In 2003, most of the time I was doing 5 and 5 or 6 and 6. It should be noted that in the summer, I, and my teammates, ran longer and didn’t stick to the straight split doubles. That could be important.

Now, this wouldn’t be a big deal, except it kind of defies the conventional wisdom. If it was just me doing this and having success, you could dismiss this for talent. However, for the past 10 years KO has had one of the more consistant and successful distance programs in Texas, sometimes with not the most talented of guys. For example, this years teams was just ranked #21 in the nation by Marc Bloom. So, it obviously is not taking anything away from the development of good runners.

Conventional wisdom would expect the aerobic system to be the one that took the hit if the mileage is split in half. However, this does not show up at all with the athletes. Through the years, numerous guys have run 5:30’s for a staple yearly 10mi tempo run that is tradition. That means there high end aerobic abilities aren’t taking a hit at all. Two more examples are that one guy who was only a 10min type 2miler at the time, ran a 1:13 half marathon off of the training, which one would not expect for a HS kid, since it takes years to get the aerobic system up to where it can be. Similarly, this year, a runner came through 5mi in mid 25’s on a tough course on a 7.5mi threshold run. The point is, the aerobic system’s, developed through a good deal of high end aerobic work, are not taking a hit because of the split mileage.

Which leads me to my next example. I was looking at some training done by former world class marathoner Kenny Moore. When I read it, I quickly noted that his easy days were filled with days of just 4-5mi runs or days of 3 and 3 or 5 and 3. Seeing this in an elite runner really made me reevaluate things. The key was that Kenny was hitting his workouts every couple days and had a good long run.

If splitting the mileage on easy days doesn’t affect the runner’s performance or aerobic abilities, then what does it do and can it be beneficial?

Here is my theory. Once general endurance is built during the base for that season, and especially in older athletes who have years and years of general aerobic work, you’re not going to get much benefit from running 8mi at 6:30 pace. It’s going to be the same stimulus that it’s gotten for months. So, it’s not going to force the body to go through some adaptation phase. It’s basically going to be maintenance. But, we know that it is much easier to maintain than to build. So, it is not necessary to do a longer 8-10mi run during some easy days.

What happens when you split it with shorter doubles is that it might enhance recovery. The runs are shorter so that not much mechanical damage is going to happen, same with oxidative damage. Secondly, and perhaps most importantly, splitting may aid in glycogen replenishment. It’s much easier to restore glycogen stores after an easy 4-5mi run then after a 10mi run. Yes, you run twice, so you have to replenish glycogen twice, but I’d still argue that it is easier to replenish glycogen twice with several hours in between. Lastly, running twice may mean that you get some sort of hormonal release twice in the day, which could improve recovery.

If we look at growth hormone release during easy running, there’s a swift rise intitially for the first 30-40min of a run, and then it levels off significantly to 60min. In one study, it showed an increase of about 550 percent from 0-40min, yet from 40-60min it only went up another 40-50percent.

The second part of my theory involves the rest of the training done. My hypothesis is that these shorter double days will only work if the athletes have a good deal of high end aerobic workouts, and there is a long run on the weekend. Kenny Moore mentions his 25-30milers some weekends as being key for him. Similarly in HS, the weekly long run of ~11-15mi seems to be enough to sustain general aerobic endurance during the season.

Lastly, it’s likely that there is an individual component to this question. Some runners may adapt better with a split while others may need the single run. What runners need which is beyond me at this point. You could make all sorts of hypothesis at this point based on aerobic abiltities, fiber type, glycogen storage capacity, and a whole host of other things.

To sum things up. What do I truly think? I think the idea has a lot of merit. If I truly could find a reason for the HS kids to do 9mi all at once instead of doubling 4.5 and 4.5, then I would make them do that (even with the boredom factor of loops…). However, with the past 4 years of helping them, and with my own experience of 4 years in HS, I really can’t find any physiological reason or, more importantly, practical performance difference to make the change. If it ain’t broke, don’t fix it. Sometimes we can’t explain why things work, yet they still do.

What does this mean practically? Test it out if you want to. During the season replace one day with an easy double of 4 and 4 or something similar. Monitor how you feel and how you respond the next day. You might be surprised.

Hopefully all of that made sense. This is just a pet theory of mine and it admittedly has wholes, so feel free to tear those apart, but if you look at it without being trapped into the traditional idea of longer is always better, even on easy days, it kind of makes sense. Thoughts, comments, critiques, welcome.

Part 2- Evidence for doubling: training in glycogen depleted state

Get My New Guide on: The Science of Creating Workouts


    1. John on October 18, 2009 at 12:34 pm

      Steve, I've been doing split doubles at least once a week for over a year now. Usually 6/6, but sometimes 5/5 or some near combination of it. When I race I usually do two split recovery runs in a week, when I'm not, it usually sticks to just once a week. I haven't felt any different, actually more consistent in my training if anything. I'm currently out of XC eligibility, and without doing any significant specific work, just an aerobic workout every two weeks, and a long run every couple weeks, I've managed to get into near 8k PR shape and within 15 seconds of 5k PR shape. I hope that helps you start to solve the puzzle, I know split recovery days has definitely won me over.


    2. Craig on October 18, 2009 at 3:06 pm


      I think that, like so much of training, the preference for doubles v. singles is largely personal. However, because of the bias for singles in training dogma, there are a lot of people (especially younger athletes) running singles when doubles would help them a lot.

      When I look back at different runners I know with relatively the same success, I can't really find a pattern for singles/doubles preference on easy days during the season. For building endurance, sure- longer runs are good. But during the season, the point of easy mileage isn't to build endurance- it's to maintain what they've got and promote recovery in between specific sessions. For me, running two reasonably short doubles has always promoted recovery better. As I've gotten older, I've tacked on a few miles to one of the runs and generally, the pattern that seems to work for me and most college athletes I know above 80 a week is 20-40min AM, 50-70min PM.

      For high school kids especially I think two easy doubles for recovery is a great idea- they warm twice, shake their legs out twice, get the blood flowing twice- but neither run is long enough to tire them out.

      However, there is personal preference to consider. I had some teammates in high school who, if training twice a day, viewed it as a grind that took the fun out of running. They'd rather do an easy 8 in the afternoon than go 4 and 4, and yet this didn't impact their recovery measurably. To attempt to continue forcing these kids to double after they had tried it for a while would have been a bad idea.

      To sum, I think everyone, especially high school kids, should try the split easy doubles way of recovery. I suspect, though, that the groups will split about 50-50 based along personal preference.


      PS- I'm jealous you had CC practice first period in high school! I had to be up at 4:45am to double in the mornings before school- and we're talking New Hampshire winters here!

    3. Anonymous on October 22, 2009 at 4:15 am

      I really like what you had to say in this post. I think the key point you make is that the split doubles are only once you have built up your aerobic fitness to a certain point. Once in season when the focus begins to shift to other aspects of training, the emphasis of easy days are now on recovery instead of aerobic gains.
      I don't know if I would split runs everyday, but I think it is a good idea to do it on designated recovery days. So if a standard 7 day week cycle looks like this(obviously differs for everyone):
      Mon-Normal Run
      Wed-Normal Run
      Thurs-Recovery Run
      Sat-Recovery Run
      Sun-Long Run
      then I think splitting runs on thurs and sat makes a lot of sense, especially for guys who are running a lot of miles. I don't know if I would cut out the full runs on Mon and Wednesday because you are then relying on your long run for the majority of your maintenance. Finally, Hudson always preaches the importance of working on all the different systems at all different points in training. even in the later part of the season can you be working on your aerobic fitness. I don't think you want to neglect the most important system to distance running.
      Let me know what you think.

    4. Anonymous on October 23, 2009 at 2:45 pm

      I began making big improvements in 1973 when I started running doubles fairly regularly. By 1977 I had stagnated and not had any PRs for over a year and changed back to singles. That brought another wave of PRs though none as dramatic as had come in the first wave.
      In the 70s there was a marathoner/ultra-marathoner called Ken Young who came up with what he called the "Collapse Point" theory. He worked out that the absolute minimum you needed to do in order to race a given distance was to average a third of that distance per day for something like 2-3 months (can't recall which) prior to the race. (More miles increased your likelihood of running faster.)
      He didn't think it mattered HOW you broke up those miles, i.e., a prospective marathoner needed a minimum of nine miles a day. Period. One nine would do, so would three threes, an eighteen every other day, etc. Young ran 2:25 without any runs longer than twelve and a half miles but was up around 110-120 as I recall in his prep.
      At another time Runner's World looked into this and published a study comparing improvements to endurance following runs of 30, 60, and 120 minutes. I won't have the numbers exactly right, but the study showed that a one hour run improved endurance by about 20% more than a thirty minute run but a two hour run improved endurance 120% (I'm a little hazy here) than a one hour run.
      Their conclusion was that you were better off running two hours one day and either taking the next off or just running for a half hour.
      But when I read the article I got to thinking that doing two half hour runs would improve endurance 160% more (80% + 80%) than a one hour run and should even be better than a two hour run. This conjures up memories of Tony Simmons who was 10,000 meter fourth placer at the 1976 Olympics and a 2:12 marathoner on two runs of 4-6 miles each day.
      In later years I've found that I'm falling apart no matter what I do, singles or doubles. I once slowed and even reversed the deterioration for a while by going back to doubling with fairly short runs and then did the same later by doing three runs a week in the 15-18 mile range and running 8-9 miles on the other days, all in singles.
      Singles generally do save money on your water bill.
      Rich Englehart

    5. stevemagness on October 23, 2009 at 3:41 pm

      Wow, some great responses. Thanks a lot.

      John-Thanks for adding your experiences with split doubles. I think you got it right in doing that for recovery runs. Good to see someone else have that experience.

      Craig- Some great points as usual. As always, individualization is key and it often gets lost in this singles vs. doubles debate. I think you hit it right on when you said:

      "For building endurance, sure- longer runs are good. But during the season, the point of easy mileage isn't to build endurance- it's to maintain what they've got and promote recovery in between specific sessions."

      The switch in purpose of easy/recovery runs during the season vs. pre-season is an important point. It shows that MAYBE singles are better at one point, when doubles are needed at another. SImilar to how at one point of the season threshold runs are emphasized, but at another some specific 5k work might be the key. BUT just like in training, you can't completely leave the stimulus behind, so that might be why you still need a long run or a couple longer single runs.

      I'd be interested in hearing your thoughts on why some runners seem to respond better to singles vs doubles. Obviously mentality plays a role but is there a physiological mechanism too? Also, should we periodize recovery/easy runs more???

      Kyle- I think you hit the nail on the head. Just like I said above to craig, it seems that modulating the recovery runs as singles or doubles is something that needs to be looked into. Also, I really think your schedule of using split doubles on the true recovery days may be the way to go. Just like you said, it allows for that enhanced recovery, yet doesn't leave anything behind because you still have other days of longer runs (ala hudson's point). Nice points.

      Rich- Wow! Some great information and insight. It is much appreciated. I'm going to have to reread your post a couple times and let it digest because there are some very interesting observations there.

      I really like the examples of the marathoners using relatively short doubles yet still succeeding. And that is very interesting that Young ran 2:25 without a long run.

      It goes to show you the individuality of training. But it also calls into question some of the accepted things we do in training.

      Thanks again for some great info. Greatly appreciate everyone's perspectives.

    6. Anonymous on October 25, 2009 at 7:32 pm


      There are more examples of marathoners who've done very well with no long runs. John Farrington from Austailia ran 2:21 on about 150 mpw, must have been some long runs there, then went to a couple 5-6 mile runs each day with a 10 miler most weekends and got to 2:11. Marc Smet of Belgium has become a minor cult figure at Letsrun for doing 2:10 without ever going longer than an hour though I'd like to see more documentation. In 1978-79 Chris Stewart of England was twice third at New York in successive 2:13s. Chris is a good friend and once told me that in one of those years he did no runs longer than 8 miles though he was doing 120-130 mpw.

      On the shorter end, late in his career when John Walker's legs were giving out he could not run for more than a half hour at a time so he did that twice a day, eventually at a pretty good clip and was still able to run almost as fast as in the years when he'd routinely do runs in the 15-20 mile range.
      On the other hand, Chris Wardlaw says the long run is the most important part of training.
      I suppose if you want to cover all of your bases you'd keep a long run in each week. From there I'm not sure it matters all that much what you do as long as you do enough of it and get enough recovery. And you need to allow for personal circumstance and preference.
      But you'll run better by running more (until you reach the point of diminishing return) and at some point you'll find that you can't run anymore miles in singles and still recover. At that point you can maintain higher volume and still recover by doing doubles. That is, there may not be a lot of difference in doing one or two runs on a nine mile "recovery" day. But it's much easier to recover from a couple seven or eight mile runs than from one fifteen.

    7. John on October 27, 2009 at 2:26 pm

      Steve, to address your question on single vs. doubles person-to-person: I think it has to do with mental approach more than anything, but to an extent I think it touches on a person's ability to recover between bouts as well.

      I know plenty of people who hate doubles. I think getting into a rhythm twice is a big factor. I feel different the first 5 minutes of my late run as compared to my early run. I'd say it's almost stiffer but not tight. Alot of people may think this is making them MORE tired or less recovered b/c of this feeling. Similarly, if you get in an easy 10 and it's no biggie, even though you're legs took much more of a beating, its not visible for another 24 hours and by then they are possibly recovered enough to not notice.

      I guess what it comes down to, for me at least, is the person's bias. Do they look at stiff legs as a short term [which it is] negative on recovery days? Do they ignore the fact that 70minutes on your feet at once provides much less actual recovery? It's all about what gets to you mentally and how you subconsciously pick up on the goods and the bads. We've talked about this alot on our team, some people just value different things and that leans them to doubles or sngles.

      Also, I think that some people just recover differently. I can run 12 times a week and be fine, but to some people the frequency gets to them quickly. For me, it's volume and intensity (which is why I run 12 times a week and take ample recovery), but for others it might be frequency and volume, or frequency and intensity that do them in. Or maybe just frequency.


    8. Anonymous on October 28, 2009 at 2:28 am

      Great site and great tips. Thanks Steve

    9. stevemagness on October 31, 2009 at 8:05 pm

      Thanks again for the comments. Love the input from others so that it’s not just me spouting off my beliefs over and over.
      -Rich, once again, those examples make you reevaluate things. I’m not sure what the right conclusion is except there are many roads to Rome and that it is important to pay attention to your own individual adaptability to training.

      I think, in general you find that the older/more mileage behind them, the less of a need for longer singles day after day, like the John Walker example shows.
      Thinking in scientific terms for a second, I am betting that the high mileage, even if it is in split doubles accomplishes the goal of a long run for a marathoner to some degree. I mean b/c of the mileage you start your 2nd run partially glycogen depleted, so the 2nd run may mimic the effects of that long continuous run to a degree. But who really knows.
      I really think you nailed it with basically run as much as you can however you like while still having the ability to recover. The key being, the ability to recover. Perhaps those who succeeded off not running more than an hour but did lots of doubles were able to succeed b/c if they did longer runs instead of split doubles they would not have recovered.
      JK- Good points. Your individual nature plays a big roll.

      I think the conclusion on singles/doubles for recovery days is do what allows the INDIVIDUAL to recover best for the main workouts.

    10. Edward Edmonds on February 2, 2010 at 4:18 pm

      Steve, it's nice to see somebody thinking about the possible benefits of multiple short runs a day (I've taken it to the extreme), I described my shedule here: (I'm E**2) along with a somewhat detailed explanation as to why I think multiple runs work.

      Edward Edmonds

    11. Anonymous on February 18, 2011 at 6:16 pm

      I think one major benefit of doing doubles that is fairly obvious is that it can allow you to fit in a day off while allowing you to retain mileage.

      While i was preparing for a marathon i began doubling once i was over 60 miles a week. and some days i would run the morning of a workout. Usually about 5 miles in the morning @ maybe 8 min pace or slower sometimes(38-42mins ). Then i would do my threshold or tempo runs in the afternoon or a hill workout. and i would hit 7-9 miles sometimes for a 12-14 mile day. On one easy day a week i would run just once barefooted or in vibrams five fingers for maybe 5 or 6 miles. Then the other rest days were 5-8 miles.

      So i guess the main difference for me is that i was doing one run on my recovery days and then doubling on my workout days with an easy run that morning. I felt that it loosened up my legs for my afternoon workout.

      I ended up getting injured during a 25k however so i never saw the long term benefits as i had only been running this way for a month and a half or so while following workout advice from Steve.

      However i was impressed with the results. Only being a 16:06 5k, 9:55 3200, and 4:35 miler, I was happy with a 1:26:48 25k.

      2 weeks before i ran 1:14:30 for a half marathon. I closed the last 13.1 of the 25k in just under 1:13

      thanks Steve! Love the articles!

      Ryan Smith

    12. danny on February 23, 2011 at 4:20 am

      I don't know how current this thread/post is..but I'll try anyway.

      I have listened to Ken Young (the same) talk about the Collapse Point. His main point behind it is that the collapse point is the minimum needed mileage (built up over time) to acquire the necessary glycogen to finish the race. The low end for this 'theory' is around 10 miles and the top end is pretty open (he has tested it for ultras in the 40 mile range).

      I enjoyed reading this post and I'll probably come back for more. I look forward to future topics.

    13. Anonymous on March 2, 2011 at 7:50 pm

      Man, I don't have any of the accounts to use my name on here. Anonymous, I'm going to be getting a bit off topic here, and I apologize if this could fit into a better post. But I couldn't help but notice in an earlier post the pattern for a typical week included only 2 workout type efforts. I've been debating the question of how many workouts is optimal with myself for some time now. I've always been injury prone, but I can handle relatively high mileage in the summer with the absence of challenging workouts. My collegiate team does 3, sometimes 2 and a race (during the XC season). I broke down bad my freshman year, and I'm almost certain I'd be better off doing more volume and less quality. Do the best programs in the country typically run less high end workouts per week? I know it comes down to what an individual can handle, and that the most aerobic gains are typically seen with 80 plus percent of training volume being low intensity, but in general is 2 hard efforts better than 3?

      p.s. I agree tremendously about 2 a days. It benefitted me enormously in high school. I only ran 20-30 mpw but I ran twice most days and had a reasonable amount of success


    14. Mark E. on April 10, 2011 at 3:59 pm

      I always feel better doing doubles vs. singles. Those easier runs just have a near medicinal feeling to me.

    15. Smith Wilbanks on July 11, 2011 at 10:29 pm

      Steve and other commenters,

      I think what a lot of people fail to recognize in the debate between singles and doubles is the change in the nature of the stimulus that comes with running doubles instead of singles. If a runner runs singles, lets say the body has an around 24hrs to recover before the next run. But on doubles, the body may only have between 10-14hrs. Halving time your body has to rest and readjust before the next run is a HUGE stimulus.

      Imagine a beginning runner switching from 3 days a week to 6-7 days a week, or adding a few extra days, all the while keeping the mileage the same. That runner is NOT going to instantly recover better – that runner will be receiving extra training stress until the body adjusts to recover more quickly. Experienced runners should expect the same.

      Experienced distance runners are primarily concerned with gaining faster times, and is therefore primarily concerned with increasing the efficiency of the aerobic system. So experienced runners naturally spend most of their training to stress the aerobic system. But increasing the frequency of runs (with the same intensity, total distance, etc.) doesn't stress the ability of the aerobic system any differently, so there is no reason to think that it directly improves our aerobic system.

      What running doubles actually does is stress the body's ability to recover more quickly, which signals the body to do just that – adapt enough to recover for a run every 10-14 hours instead of every 24 hours.

      The main implications of this (that I can see) is that if a runner conditions his body to recover more quickly from easy runs (given the same total mileage), then that runner may be able to recover more quickly and more fully from the intervals and tempos that stress the aerobic system, allowing more benefit from each workout, and possibly more frequent or higher intensity workouts in a given training week/cycle.

      The best application for doubles is in the early season/buildup phase, ideally summer for cc runners, and to maintain it through the rest of the season (thereby maintaining your body's ability to recover more quickly). There is a common rule of thumb for safely building mileage – don't increase distance and intensity of runs in the same week – likewise, you should only increase distance, intensity, OR frequency of runs in the same week.


    16. Anonymous on August 21, 2012 at 1:52 am

      2 shorter runs can be done at a faster pace than 1 long run aka faster speed means faster in the race

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