Back in the day, the importance of a distance run was thought to be that of putting constant pressure on the heart so that it will adapt. In other words the theory went that you wanted to keep your heart rate up for a prolonged period. So the logic went, the further we can go the better.

What we now know is that adapting to training is a super complicated process that involves numerous different adaptations on multiple different systems. So is it as easy as more is always better? I’ve delved into this question many times in regards to doubles versus singles. By the old school logic, singles should always be better. It makes logical sense that 10 miles once is better than 5 miles twice. But as I pointed out before, that logic isn’t always sound. It’s one of my favorite topics to delve into (more here) and it’s always worth looking into.

An interesting new study came out where they took a look at the effect of one 30min run versus 3x10min runs throughout the day in mice. It’s not quite your doubles versus singles argument, but it’s an interesting concept.

What makes the research a bit more fascinating (and also harder to translate to real world application) is that it was on mice, which means they could dissect and analyze all sorts of things that we normally can’t see. We get to see what is going on at the cellular level instead of relying on crappy surrogate markers like VO2max.

What they did was take mice and stick them on an 8 week treadmill training regime. Half the group they had do 30min a day all at once 5x a week, while the others did 3x10min split with 2 hours rest in between. Then they measured all sorts of lovely signaling pathways activation to see what was going on.

What did they find?

Performance- Pre and post training Each group improved their distance covered from 224 to 464 (30min) and 217 to 471 (3x10min), speed, and work to similar levels. Capillary- Both groups had similar increases in capillarization. No significant differences between the two groups. Pathways- Citrate Synthase activity increased in both groups to similar levels and VEGFR2 increased similarly in both groups. Slow Twitch fiber % increased in both. TSP-1 decreased by 50% in the 30min group and 68% in the 3x10min group. P38 MAPK increased similarly in both.

What do these random letter combination things mean?

VEGFR2 refers to one of the receptor for vascular endothelial growth factor (VEGF-A) which is basically one of the regulators for capillarization. TSP-1 is the protein that essentially works in contrast to VEGF-A. So if you get a decrease in TSP-1, you generally get an increase in capillarization. So taken together, increase in VEGF and decrease in TSP-1 in this study meant increase in capillaries. P38 MAPK is involved in the PGC-1 pathway which regulates mitochondria proliferation among other endurance related changes.

So what?

Yes, it’s only mice. But what is interesting about this study is that you saw similar increases in performance, capilarization, and mitochondrial biogenesis. This would run in the face of the old school running/training thought process. It doesn’t mean everyone should get out and start training three times a day and never run far. What I think it does do is give just a little more evidence for why doubling (or maybe tripling?) may work. And before I get crucified by the old school singles are king people. All I’m saying is that maybe each has their place and this study simply adds intrigue to the idea.

In my own coaching, I’m a big fan of the occasional even split short double for recoveries sake and if studies like these are to believed you’re not really missing out on the stimulus for adaptation. Just judging by past experience that was always my feeling with the high school kids I used to coach ( Running Times article here) We’d do singles for the most part in the summer and then doubles during the school year because there were only so many times you could run around the boring loop at school without wanting to kill yourself. What I found was that endurance was maintained as long as they had a single long run on the weekend.

So what’s that mean? I have no idea. But maybe to build endurance we go with singles and shift to more doubles which are easier on the body for maintenance. Then the question gets asked about other forms of exercise or what is the effect of doing cross training as a shakeout or a shakeout after a workout, or on and on. So many questions, so much to figure out.

Periodize your easy runs? Maybe. Most of the time we just ignore easy/distance runs and don’t put much thought into them. Maybe it’s time to.

References: Malek et al.(2012) Similar Skeletal muscle angiogenic and mitochondrial signaling following 8-weeks of endurance exercise in mice. Discontinuous versus continuous training. Experimental Physiology

Waters RE, Rotevatn S, Li P, Annex BH & Yan Z (2004). Voluntary running induces fiber typespecific angiogenesis in mouse skeletal muscle. Am J Physiol Cell Physiol287, C1342-1348.