On Tuesday this week, when my lunch-date plans fell through, my mind automatically turned to running. As it was such a beautiful day I was all too tempted to get outside for a quick jog along the river. However, my schedule called for a 7 mile run, (which I’d planned to do that evening), and it was unlikely that I’d be able to squash it in over lunch.

Determined to keep to the mileage set out in my training plan I turned to Google to see if two shorter runs could be substituted in for one longer run and I was pleased to read the results.

An article in Runners World (my gospel for running advice) suggested that not only is it not detrimental to split your mid-length runs, but actually that there are circumstances when two runs are in fact better than one.

Although when you’re trying to build up your endurance levels, longer single runs are still preferable, once you’ve built this up you can draw benefits from ‘running doubles’.

So how does this work? Well, in terms of maintaining your fitness levels, it is easier to maintain endurance than to build it up, so as long as you have a regular long run and your overall mileage remains the same, you won’t lose general endurance by splitting one of your mid-length runs in two.

Moreover, after your initial base training phase, you will find yourself doing more workouts at a harder level and, as such, greater importance needs to be placed on recovery. And while it might seem counterintuitive, adding a second run in on the days between long runs can actually be used to enhance recovery.

This is because in doing two shorter runs you are putting your body under less pressure than you would during one longer single run. On these shorter runs you have plenty of fuel stores and you rely primarily on your fatigue-resistant slow-twitch fibres, the result of which is less fatigue and less muscle damage. Instead, you get an increase in blood flow to your muscles twice, and two spikes in human growth hormones, which are stimulated through aerobic exercise, both of which assist recovery.

More than just helping you to recover from runs, doubles can also assist in functional adaptation, basically making you fitter, faster.

This occurs for two reasons. Firstly, even though each run is shorter, you still get the general aerobic training benefits you would from one run, but now you get this twice over. This results in the activation of the genes that cause an increase in mitochondria, or an increase in oxygen-carrying capacity, for a greater total amount of time than if you did just one run.

Secondly, by running doubles, especially after a hard workout, you are training in a pre-fatigued state. This allows you to access different muscle fibers that you might not normally train, and to push further into a glycogen depleted state than you would normally do. As a result, studies show that glycogen content, fat oxidation, and enzyme activity also increase from training twice in a day.

All of this was music to my ears and allowed me to enjoy two slightly shorter runs, one of which I was able to do with my lovely friend LP, breaking up the monotony of one long run alone (and getting me home earlier in the evening). I also found myself going over my 7 mile target, running 14k/8.7 miles in total.

The caveat to this is of course that long runs are still a vitally important part of marathon training. If you haven’t been running at a higher mileage (around 50 miles per week) consistently for at least 3 years, the bulk of your improvements are still going to come from improving your aerobic endurance, which comes from 60-90 minute runs (widely considered to be the critical time threshold for enhancing aerobic fitness at the cellular level).

That said, double runs in the 30-45 minute range, are still highly beneficial (for the reasons outlined above), and are ideal if you are struggling to fit all of your mid-length runs in during your week.

I’ve got another 7 miler tonight and a 4 miler to fit in on Thursday lunchtime before I head up north to my sister’s for her birthday at the weekend, so here is hoping the recovery theory holds true!

Happy running!