Is Your Pre-Marathon Long Run Too Far?
Why running shorter—and harder—may benefit your race time and save you from injury
By Jeff Gaudette—The marathon long run is overrated.
I’ll pause for a second to let the sound of your gasps fade. In my experience, too many beginner runners, and those running slower than 3 hours and 45 minutes, focus on trying to squeeze multiple 20- or 22-mile runs into their training segment at the expense of improving more critical physiological systems. More importantly, scientific research has shown that runs of over three hours offer little additional aerobic benefit compared to runs of two hours, while significantly increasing injury risk.
As such, rather than cramming your marathon training schedule with multiple 20- to 22-milers that increase injury risk and decrease recovery time without decisive aerobic advantages, you should instead focus on improving your aerobic threshold, teaching your body to use fat as a fuel source, and building your overall tolerance for running on tired legs through accumulated fatigue.
Since the long run is such an ingrained element of marathon training, and suggesting they are overrated sounds blasphemous to many marathon veterans, let’s take a look at some scientific research, relevant examples and suggestions on how to better structure your training to help you run your next marathon faster.
The Science of the Long Run
Many new runners training for the marathon are averaging anywhere from 9 minutes to 12 minutes per mile on their long runs (3:45 to 5-hour finishing time). At a pace of 10 minutes per mile, a runner will take roughly 3 hours and 40 minutes to finish a 21-mile run. While there is no doubt that a 21-mile run (or longer) can be a great confidence booster, from a training and physiological standpoint, they don’t make too much sense. Here’s why:
Research has shown that your body doesn’t see a significant increase in aerobic development, specifically mitochondrial development, when running over 90 minutes. The majority of the physiological stimulus of a long run occurs between the 60- and 90-minute mark. This means that after running for three hours, aerobic benefits (capillary building, mitochondrial development) aren’t markedly better than when you run for only two. Therefore, a long run of over three hours isn’t building much more aerobic fitness than one lasting two hours.
Furthermore, running for longer than three hours significantly increases your chance of injury. Your form begins to break down, your major muscles become weak and susceptible to injury, and overuse injuries begin to take their toll. This risk is more prevalent for newer runners whose aerobic capabilities (because of cross-training and other activities) exceed their musculoskeletal readiness. Basically, their bodies aren’t ready to handle what their lungs can.
Not only are aerobic benefits diminished while injury risk rises, recovery time is significantly lengthened. The total amount of time on your feet during a three-hour-plus run adds considerable fatigue to the legs, which leads to a significant delay in recovery time. In the long-term, this means you can’t complete the more marathon-specific workouts, which I believe, and research has shown, are a more important component to marathon success.
Why is the 20-Miler So Popular?
Given the overwhelming scientific evidence against long runs of over three hours, why are they so prevalent in marathon training?
First, many people have a mental hurdle when it comes to the 20-mile distance. The marathon is the only race that you can’t easily run in training before your goal race. Therefore, much like the 4-minute mile and the 100-mile training week, the 20-mile long run becomes a mental barrier that feels like an obtainable focus point. Once you can get that two in front of your total for the day, you should have no problem running the last 10K, or so your mind believes. Unfortunately, this just isn’t true from a physiological standpoint.
Second, the foundation for marathon training still comes from the 1970s and 1980s at the beginning of the running boom. Marathoning hadn’t quite hit the participation numbers it has today (you could sign up for most marathons, including Boston, the day before the race) and the average finishing time at most races was closer to three hours (today that number is over four hours). As such, the basis for how to train for a marathon came from runners who averaged close to six minutes per mile for the entire race. Therefore, 20- and 22-milers were common for these athletes, as a run of this distance would only take them about two-and-a-half hours to finish at an easy pace.
Moreover, the 20-mile distance is synonymous with “hitting the wall” or “bonking” during the race itself. “Hitting the wall” frequently occurs at 20 miles because your body can store, on average, two hours worth of glycogen (fuel) when running at marathon pace. Two hours for a six-minute per mile marathoner occurs at almost exactly 20 miles.
In short, the basis for a lot of our understanding of marathon training is passed down from generation to generation without regard for the current paces of many of today’s marathoners. Therefore, we also need to reassess where the long run fits into the training cycle and how we can get the most benefit from training week in and week out.
How to Train Smarter
If you’re training to run 3:45 or slower, I suggest that you downplay the role of the long run and focus instead on improving your aerobic threshold (the fastest pace you can run aerobically and burn fat efficiently) and utilize the theory of accumulated fatigue to get your legs prepared to handle the full 26 miles, without needing to run the full distance.
For example, focus on stringing out your workouts and mileage over the course of the week, rather than having 40 to 50 percent of your weekly mileage come from the long run, which increases the total amount of quality running you can do and decreases the potential for injury.
The million-dollar question still remains, however: How do you get your legs prepared to run for 26 miles? The answer lies in the theory of accumulated fatigue. By shortening your long run to 16 to 18 miles and buttressing it against a shorter, but steady paced run the day before, you’re able to simulate the fatigue you’ll experience at the end of the race.
In addition, when you have shorter long runs, you’re able to increase the total quality and quantity of tempo and aerobic threshold workouts throughout your training week. Instead of needing four to five days to fully recover from a three-hour-plus run, with a shorter long run, you can recover in one or two days and get in more total work at goal marathon pace or faster. Developing your aerobic threshold is the most important training adaptation to get faster at the marathon distance because it lowers the effort level required to run goal pace and teaches your body how to conserve fuel while running at marathon pace. The more work you can do to improve aerobic threshold and your ability to burn fat as a fuel source, the faster you can run the marathon.
Finally, with a focus on shorter, more frequent long runs, you can implement faster training elements, such as fast finish long runs or surges, which allow you to increase the overall quality of your long runs. Running your long runs at a slightly higher intensity level teaches your body how to run marathon pace while tired, and also increases your body’s ability to store energy for the end of the race and use fat as a fuel source more efficiently.
When you balance out the gains from finishing a long run fast and upbeat with the potential drawbacks from an extended three-hour-plus long run, you can see why a shorter, faster long run is the better training option for newer marathoners and those aiming to finish over 3:45.