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