Look at 100 different training logs from elite road and track racers, and one unifying factor will stick out: most of them are running twice a day, usually two to five times per week. Most recently, 2:03 marathoner Eliud Kipchoge’s training log for the Berlin Marathon became public, showing mind-blowing workouts and long runs. But buried in there was a seemingly simple addition—he would run 35 to 50 minutes slowly (for him) most afternoons after longer morning runs.
It’s not only other-worldly marathoners who are adopting the double-run concept. In road and track racing, it’s more exceptional when an athlete doesn’t do double-run days (like 1500-meter World Champ Bernard Lagat) than when they do. Haile Gebrsellassie, former world-record holder in the marathon, is famous for saying that he ran two times a day every day except for Sundays and Christmas. A few training groups are even known for running three times a day during heavy training.
Why has practice coalesced around running doubles? The answer is unsatisfying: it’s likely a lot of different factors that depend on the individual, and there is no definitive scientific evidence indicating that doubles are the best approach to training for performance.
Doubles are far less common in trail running, even among professionals. Could there be an untapped training secret lurking in the training logs of road and track runners?
Probably not. But doubles could be a helpful addition to your training toolkit, even if you aren’t running a ton of miles.
First, let’s look at the potential benefits of double runs.
1. The increased running volume leads to improvements in aerobic development, while reducing injury risk and improving recovery.
Generally speaking, run more while staying healthy and you will get faster. By spreading out training volume, doubles allow runners to run more without getting injured. A 10-mile run probably involves more muscle- and tendon-fatigue than two five-mile runs. A runner who does a 5/5 double might recover better and stay healthier than if he/she ran 10 miles all at once.
2. Enhanced recovery and adaptation from the hormonal stimulus of the second run.
Many elite sports, like soccer and swimming, involve two practice sessions a day. One reason cited is that growth-hormone production increases with short bouts of endurance exercise, which could speed recovery and cause quicker adaptations to training stimuli (for example, see this study tracking growth hormone response from different exercise bouts).
3. Double runs may aid in glycogen replenishment and improve aerobic efficiency.
As posited by top coach Steve Magness, it’s simpler to replenish energy stores after a shorter run than after a long one. After a seven-mile run, you might just need a big bowl of cereal. After a 14 miler, you might need a whole box. If your goal is recovery, two short runs might be better than one longer run.
Meanwhile, on workout days, doing the second run in a glycogen-depleted state could lead to quicker adaptations. One study found that training twice a day in a glycogen-depleted state can enhance gene transcription related to training adaptations (however, that same study also found it compromised high-intensity training capacity).
Another study showed increased time to exhaustion in resistance training from training two times per day with glycogen depletion (however, that study was focused on knee-extensor exercises).
4. Double runs may be more convenient for time-limited people.
While doubles might be most associated with professional training groups, my favorite example of doubling is from amateur U.S. runners in the 1970s and 1980s. In those decades, most recreational road marathoners were teachers, doctors and others running before work and after work. Even “pros” were working back then, and doubling made it easier to get the volume in. Nowadays, even most of us running lower volumes can fit in a 5K at lunch in addition to a morning run. However, for some people, running twice in a day could make it feel more like an obligation, rather than a joy.
Now it’s time for the million-dollar question: should you double?
As you might imagine, the answer is maybe, in moderation, depending on your lifestyle and goals. Here are five considerations:
1. If you are volume limited, prioritize single long runs over shorter double runs.
Up to a certain point, sustained aerobic stimulus is likely better than multiple shorter runs. For most trail runners, a 10-mile run is better than two five-mile runs because of increased aerobic and musculoskeletal stress that spurs adaptations. So when designing your weekly training schedule, the first priority should be sustained aerobic stimulus.
2. When first starting to use double runs, add them once a week on a workout day. Then add similar doubles on easy days.
Start by adding a short, easy double after a workout, when the hormonal stimulus may be most beneficial to enhance adaptations. Plus, it may speed up the recovery process by flushing waste products. If that works for you, consider adding short doubles on other days, while ensuring that easy days still achieve their recovery goal (run commuting is a great option for some).
3. Don’t do two moderate or hard runs in one day unless you are working with a coach.
Some training programs incorporate two hard workouts in a single day, usually sparingly. Most famous of these hell days are the Canova Special and Specific Blocks, pioneered by coach Renato Canova, consisting of something like one-kilometer repeats in the morning followed by a tempo run in the afternoon in a glycogen-depleted state. However, these types of days are extremely risky for health, and likely aren’t needed unless you are looking for that extra 0.1-percent fitness boost. You can consider adding short strides to a double run if you’re feeling ambitious.
4. Never double on a long-run day.
Because the goals of long runs are specific adaptations for resilience and aerobic development that come from sustained work, doubling on a long-run day doesn’t help the primary training goal (and could detract from it by causing injury).
5. All doubles are optional—never do them if you are worried about injury or struggling with motivation.
Since doubles are not a magic elixir required for fitness, it’s essential to only do them when they fit within your life. For my athletes, I make every double optional.
In fact, most pro trail runners don’t do them (possibly because the races are usually longer and hillier, necessitating a focus on sustained aerobic and musculoskeletal stress). But adding a short double here and there could compound some of your training investments by adding aerobic stimulus, improving aerobic efficiency and producing bonus hormones.
Just remember: it’s all a moot point if you’re injured or stressed, so make sure doubles fit in the context of your life. The goal is to love running, and, if doubles don’t help that goal, then they are counter productive.
David Roche runs for HOKA One One and NATHAN, and works with runners of all abilities through his coaching service, Some Work, All Play.