For most runners, doubles are a foreign concept, assumed to be the province only of those cranking out 100-mile weeks. I would like to convince you to think otherwise. Intelligently adding some double days to your programme can help advance your fitness, even if you wind up not significantly increasing your mileage.
When two runs beat one
During a base-training period, when you’re trying to build general endurance, longer single runs provide the stimulus you’re looking for. But once you’ve built your general endurance, the need for longer single runs every day shifts for two reasons. Firstly, it’s easier to maintain endurance than to build it; therefore, as long as you have a regular long run and your overall mileage hasn’t dropped considerably, you won’t lose general endurance. Secondly, after your base phase the emphasis shifts to harder workouts – and, more importantly, recovering from them. It might seem counterintuitive at first, but adding a second run can be used to enhance recovery and even to increase adaptation.
A common yet surprising result of including two runs in a day is that you often feel more recovered the following day. The most obvious reason is that by running shorter twice, you don’t beat your body up as much as you would on a longer single run. On these shorter runs you have plenty of fuel stores and rely primarily on your heavily fatigue-resistant slow-twitch muscle fibres. The result: no lingering fatigue or damage. Instead, you get an increase in blood flow twice to help with recovery and, perhaps more importantly, an increase in hormones (such as growth hormone) that help with recovery. Getting a good hormonal spike to aid recovery twice during a day does wonders for getting you recovered for the next day’s workout.
But the benefits of doubles go beyond just recovery. One workout by itself doesn’t translate to a sudden increase in fitness. Instead, each run triggers the body to signal certain genes to make functional adaptations. It takes multiple runs or workouts to translate that signal into some sort of functional change. Essentially, you need an accumulation of stimuli to get the training adaptations you work so hard for.
Doubling plays a role in this in two ways. A general aerobic training stimulus twice per day instead of once means that the genes that cause desirable changes, such as increased mitochondria (the structures within cells that produce energy) or an increase in oxygen-carrying capacity, are activated for a greater total time than if you did just one run. So you have a much more sustained pressure on adaptation.
Also, by running doubles, especially after a hard workout, you’re training in a pre-fatigued state. Doing so allows you to access different muscle fibres that you might not normally train, or to push further into the depths of glycogen depletion than you would normally.
As a result, you get a slightly different stimulus for adaptation. Research looking into training twice a day versus once a day for the same total weekly volume has shown that the increases
in aerobic enzymes (proteins that facilitate energy production) can be potentially greater when doing two bouts of exercise relatively close together.
Every second run counts
Now that you know what doubles can achieve that singles can’t, how do you incorporate them into your schedule? The most important factor is determining what the purpose of the double is. Once that’s known, then deciding when and how to use a second run is easy. Before we look at some scenarios, it’s important to realise that, however you use doubles, you’re adding a new stimulus to your training. Keep the pace easy on these new runs and, because most of these secondary runs are so short, you don’t need to devote time to your usual pre-and post-run stretches and exercises – just run!
When the goal of doubling is to enhance recovery, split your mileage for the day as evenly as possible. For example, if you had planned for an eight-miler, do two runs of four miles each. By splitting it evenly, you minimise fatigue but get an even boost of all the aforementioned good stuff twice in one day.
For my athletes, I most often schedule recovery doubles like this the day after a hard day. A typical example would be to do a hard workout on a Tuesday, then follow that up with a Wednesday that includes two short runs, do a normal-length single run on Thursday, and another hard workout on Friday. This type of schedule allows for a nice mix of split doubles to enhance recovery while still including some single runs to maintain general aerobic ability.
On the other hand, if your goal in doubling is to get a little more bang for your training-adaptation buck, schedule in a double for when you know you’ll be a little fatigued. Place a second shorter run of three to six miles the afternoon after a hard morning workout. It’s unlikely you’ll be fully recovered from the morning workout, so you’ll be doing the second run in a slightly pre-fatigued state. You’ll not only squeeze out more adaptation, but you’ll also enhance your recovery.
Finally, doubles can be used to prime the pump for workouts or races. In this case, you would want to do the double during the morning before an afternoon workout. The short morning run would serve to prime the body by flushing out the system and manipulating the muscle tension so that you’re in a better position, physically, to run the hard workout in the afternoon. When using this method, keep the run short (between two and four miles). You can also do this a few hours before a race – most easily for an afternoon or evening race – perhaps with some light strides at the end to top it off.
The most important thing when starting to add doubles to your programme is acknowledging that, like any new training implementation, you have to give yourself time to adapt to the new schedule. After this adjustment, you’ll be on your way to seeing the full benefits and it’s unlikely you’ll look back.