Long Runs: Why and How to Run Them

Essential Efforts to Elevate Endurance

by Pete Pfitzinger, M.S.

One of the questions I get asked most frequently is, “How fast should I do my long runs?” In the past, my standard recommendation has been to run 10 to 20 percent slower than goal marathon race pace. Upon reflection, this advice is too simple. The correct answer is, “It depends on how that particular run fits into your overall training schedule.” In this column, we will briefly discuss the physiological benefits of long runs. Then, we will look at how hard to do your long runs to prepare optimally for a marathon.

Why run long?

Long runs stimulate a variety of physiological adaptations, which lead to improved marathon performance. One of the most important objectives of long runs is to deplete your glycogen (the storage form of carbohydrate) stores, which signals your muscles and liver to store more glycogen. Long runs also train your muscles to rely more on fat and less on carbohydrate at a given pace so your glycogen stores last longer. In addition, long runs play an important role in building confidence for the marathon.

What is the optimal intensity for long runs?

The appropriate intensity for your long runs varies depending on the objective of each training session. Some of your long runs should be truly challenging, while others should be downright comfortable. How hard you should do a specific long run depends on the amount of time until your goal race, and the effort required for the other workouts in your training program. The following four long run intensities all have a place in your marathon preparation:

1) 10 to 20 Percent Slower than Marathon Race Pace: This is the optimal effort for most long runs. The first few miles can be nice and easy, but by five miles into your long run, your pace should be no more than 20 percent slower than marathon race pace (MRP). Then gradually increase your pace until you are running approximately 10 percent slower than MRP during the last four to eight miles.

Because the faster you run the more glycogen you burn, doing your long runs relatively quickly is a more effective way to deplete your glycogen stores (and hence stimulate the muscles to store more) than running slowly. Similarly, if you jog your long runs your body will adapt to burn fat at a very slow pace but will not necessarily be trained to increase the proportion of fat utilized at speeds approaching race pace. Running at 10 to 20 percent slower than MRP is hard enough that you will also use a similar posture and running style as during the marathon, whereas slower long runs reinforce sloppy running technique. Long runs in this intensity range are difficult enough that you should schedule one recovery day before and one or two afterwards.

2) Marathon Race Pace: The closest way to simulate running a marathon is to do a long run at MRP. Long runs at MRP, however, are also similar to a marathon in that it can take a long time to recover. If you try to do your weekly long run at MRP, then you will almost certainly be too tired for your other important training sessions, and will likely last about three weeks before wearing yourself out.

Although it has been reported that Khalid Khannouchi does his long runs at MRP (in his case under 4:50 per mile), even Khalid’s body cannot withstand this level of effort week after week. Long runs at MRP, therefore, should be strategically inserted into your training program. Make sure that you have had a couple of recovery days before a MRP long run (do not try to do one the day after a race), and schedule at least three recovery days afterwards as well.

3) Long Slow Distance: Long slow distance (LSD) has always been popular with runners whose goal is to finish the marathon, but has never been widely practiced by more competitive runners. For the reasons discussed above, running slow (i.e., 2 to 3 minutes per mile slower than MRP) does not provide as specific a stimulus for marathon preparation as do faster long runs. LSD runs, however, do have a place in your marathon preparation. It makes good sense to do your long run slowly if you have had a tough week and feel that doing a higher quality long run will wipe you out for the following week. A slow long run is also appropriate during a planned recovery week, or the day after a hard Saturday race.

4) Starting Slow and Increasing to Marathon Race Pace: This combines elements of the three types of long runs we have already discussed. Starting slow and gradually speeding up to MRP is an excellent way to simulate the last 10 miles of the marathon (i.e., running at marathon pace while fatigued), without requiring as much recovery time as would be necessary if the entire run was at MRP. You can either gradually increase your pace during the course of the run so you reach MRP for the last four to eight miles, or do the first three-quarters of the run slowly and then speed up more abruptly to MRP.

As a marathoner, your objective is to prepare optimally to run 26.2 miles, which includes reaching the starting line (and finish line) healthy. Common sense tells us that there is a tradeoff between running far enough to prepare physiologically for the marathon and remaining injury-free. The probability of injury tends to increase markedly as runs go beyond 20 miles, because when your muscles are highly fatigued, they lose their ability to absorb impact forces, which increases your risk of muscle strains, tendinitis, and even stress fractures. Towards the end of long runs, running technique tends to deteriorate, which can further increase the likelihood of injury. The risk of injury also increases if you do too many long runs, particularly if you have substantially increased the distance of your long runs during your marathon preparation.

How far and how many?

How far your long runs should be, and how many of them you should do, depends on your marathoning experience, injury history and goals for the marathon. The more experienced you are, the more long runs you should be able to handle. On the other hand, the more injuries you have endured, the fewer long runs your body is likely to be able to deal with before breaking down. Depending on your goals, you may be willing to take greater risks during training or prefer to err on the side of caution.

The “long run prescription” table provides guidelines for the number and distance of long runs for marathoners with varying goals and injury histories. Admittedly, every marathoner is an experiment of one, so these recommendations will not work for everyone, but they are appropriate for most marathon runners.

For the majority of runners seeking a personal best, four to six long runs are sufficient. For those of you who are blessed with excellent biomechanics, a few more long runs over 20 miles will likely marginally improve your marathon performance. Seven to nine long runs in the 20 to 22 mile range will provide incremental physiological adaptations and provide even greater confidence for the last 6.2 miles. Finally, if you are an experienced marathoner who is intent on doing everything you can to ensure you achieve a personal best (and you are not injury-prone), then 10 to 12 long runs of at least 20 miles is the ultimate preparation. Of those, most should remain in the 20 to 22 mile range, with one or two runs of 24 miles. Doing more than this may look good in your training diary, but is likely to hinder, rather than improve, your marathon performance.

How quickly should you increase your long runs?

A method that works well for many runners is to increase your long run by one mile per week, skipping every third week. If your current long run is 14 miles, then you would build up to 20 miles over eight weeks. In this example, your long run schedule would be: week 1: 15 miles, week 2: 16 miles, week 3: shorter long run, week 4: 17 miles, week 5: 18 miles, week 6: shorter long run, week 7: 19 miles, week 8: 20 miles. This rate of increase creates an appropriate balance between lengthening of your long run fairly quickly while giving your body time to adapt positively to the increased training load.

When should marathoners get serious about long runs?

There is no reason to do very long runs year-round. The “long run prescription” table provides recommendations for when to schedule your first 20 miler, based on the number of 20+ mile runs you will do. For novice marathoners, the first should be done five weeks pre-marathon, and the second two weeks later. For many experienced marathoners, the most effective pattern is to do two consecutive weeks with a run of 20+ miles, with a shorter long run every third week. This pattern also works well for fitting in pre-marathon tune-up races. Avoid getting into a routine of doing a very long run week-after-week because you will become too tired to do your other important training sessions such as tempo runs.

Your last run of 20 miles should generally be three weeks before your marathon, followed by a well-earned taper.


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