Do You Really Need to Cap Your Long Run at 3 Hours?

You’ve probably heard online or from your running pals that people shouldn’t be doing long runs that exceed 3 hours. But is this accurate? As a coach, I have mixed opinions on this “rule” – which like so much else in running, is much more nuanced than social media has led us to believe.

The quick answer as to whether you should do long runs over 3 hours: it depends! Some runners may go over 3 hours in training without excessively enhanced risk and it may offer them a mental reprieve knowing they can achieve a particular distance or duration. Others may need to cap their long runs at a shorter duration of 2:30-3:00. The decision depends on pace, injury history, recovery time frame, fueling, and several other factors. Let’s dive in to all the details…

Disclaimer: This post was written and reviewed by Chrissy Carroll, RD, CPT, RRCA Running Coach and USAT Level I Triathlon Coach. It is for informational purposes only and should not be construed as individual training advice.

Why is the 3 hour rule suggested?

A prevalent view within the running community is that long runs over 3 hours provide little additional aerobic or metabolic benefit but drastically increase injury risk.

For example, world renowned running coach Jack Daniels generally recommended capping the long run at 2:30-3:00, and not exceeding 25-30% of mileage in the long run. Hanson plans cap the long run at 16 miles for marathon training. Most other running coaches online suggest a similar time cap of 3 hours, or a mileage that would fall around that equivalent.

While this is the prevalent view, it does not mean it is 100% grounded in research. I think it is helpful to break down both “little additional aerobic or metabolic benefit” and “increased injury risk” beliefs with the current research we have available.

Are there diminishing returns running over 3 hours?

Long distance running is known to help with aerobic development. These benefits are not linear, and there are diminishing returns after a particular duration.

However, research is not clear on exactly when those diminishing returns happen, and whether there are still some additional benefits that can be gleaned after 3 hours of running.

There is no individual study out there that has specifically examined the 3-hour-run cut off. The closest piece of practical research we probably have is a 2020 study in the Scandinavian Journal of Medicine and Science in Sports that examined longest run length on the impact of marathon performance among recreational marathoners.

In that study, a longest long run of less than 15.5 miles was linked to a slower finish time. This doesn’t give us much info on its own, though. This could mean runners were slower because they didn’t run long enough in training, or (perhaps more likely) that slower runners did shorter mileage for long runs in training. They did also find that a longest long run of more than 22 miles was not associated with improved performance compared to 18.5 to 22 miles.

Aside from this, there is research on certain aspects of running, duration, and individual physiological factors that may be helpful to examine…

Mitochondrial Capacity

Running increases mitochondrial density in muscle cells. If you’ll remember from high school biology, mitochondria are the powerhouse of the cell responsible for energy production.

Scientists question whether extended duration runs offer any additional benefit to mitochondrial density. Much of the questioning comes from one piece of research on rats conducted in 1982. That study found that at each running speed, the longer the rats ran, the more their muscles adapted – but only up to a point. After a certain duration, extra running time didn’t lead to bigger changes.

Unfortunately, much of the current research on mitochondrial density in muscles is focused on intensity rather than duration of exercise, which leaves us at a little bit of a disadvantage for this topic. A  2016 review noted:

“Studies performed in rodents have demonstrated that increasing the training volume by raising the duration…or frequency…of exercise augments mitochondrial adaptations to aerobic exercise; however, insufficient data are available to fully ascertain the roles of these variables in mediating mitochondrial adaptations to exercise in humans.”

TLDR: Exercise after a certain duration may not offer additional benefits for mitochondrial density, but we don’t know what that duration is in humans.

Increased Capillaries

Exercise leads to the formation of new capillaries throughout the muscle that improves oxygen delivery to the muscles.

A 2022 meta-analysis noted that in people who were already exercising regularly, changes to the types of training (intensity and duration) did not result in additional increased capillarization of the muscles. They noted that more research is needed to see what, if any, methodologies may affect this.

TLDR: Increased capillaries in the muscles likely cap at a certain volume of training, so 3+ hour long runs probably don’t offer an additional benefit here.

Muscle Fiber Shifts

There are also adjustments to the muscle itself that can occur with endurance training. Muscle fibers can shift from faster, fatigue-prone types to slower, endurance-friendly types. Research has shown very clear evidence of this in novice marathon runners.

The degree of these changes can depend on both the duration and intensity of the exercise. Most studies on duration have been done in animals though. For example, an older study on rats found the magnitude of change was higher with 90 minutes of running compared to 30 minutes.

Research suggests this benefit is not linear, though. Those who are already well trained might experience a dampening or cap on fiber shifts. In fact, a rat study suggested “excessive increase in endurance training” could actually lead to a decrease in working muscle capacity. However, other authors note certain individuals may have greater “plasticity” towards positive fiber changes with extensive training.

TLDR: Exercise can affect muscle fibers, but it’s unclear if this benefit is positively impacted by longer long runs. It may vary based on genetics. A well-balanced training plan is likely most important.

Fuel Utilization

When running long distances, the body is generally using a blend of both carbohydrates and fat for fuel. Long runs play a critical role in training by teaching the body how to become more efficient at using fat for fuel.

We can only store so much carbohydrate in the muscles (you’ve probably heard of this as glycogen stored in the muscles). Becoming more efficient at burning fat is thus a helpful and normal adaptation of long runs.

There is a risk to excessively long runs in that you can reach a point of glycogen depletion, which means your muscles have “run out” of carbohydrates to fuel you. This can make recovery tougher and affect the overall effectiveness of training.

But when you hit this point depends on several factors: the pace that you are running, your diet, fueling during exercise, and the size of your leg muscles.

There is no one specific duration that is equivalent with glycogen depletion for all runners. Running a long run at a slow enough intensity (as determined by the percent of VO2 max of your run) would help reduce the risk of glycogen depletion even after 3 hours.

TLDR: If your long runs are 3+ hours at a high intensity, that risks glycogen depletion and poor recovery times. Adjusting the intensity can mitigate this risk.

Do 3+ hour long runs increase injury risk?

The previous 2020 study in the Scandinavian Journal of Medicine and Science in Sports on marathon runners also looked at injury risk. They found there was no association between long run distance and running related injuries in marathon runners. This did not include duration, so it is unclear how many runners were over 3 hours in the long run, but it is one of the better pieces of research we have.

What is the biggest risk for running injury risk in the research?

Having a previous running injury. That is what a recent meta-analysis on the topic noted for injury risk for long-distance runners, and what almost all other studies on this topic note. Prior injuries may have either not completely healed, or may have led to changes in running form – both of which can increase the likelihood of injury again.

Other possible risk factors identified in other studies and a systematic review include:

• Other injuries unrelated to running
• Having fewer years of running experience
• Dramatic increases in running distance without appropriate time to build to that distance
• Newer research does suggest some potential links to running form as well, though this is debated.

There is conflicting data about gender, age, BMI, and overall running volume as it relates to injury risk.

One could assume that if a runner is out there for longer than a few hours hours, they may start to have increased cumulative joint load, fatigue, and a breakdown in form. Long duration runs can lead to changes in cadence, stride length, and ground contact time, which can affect the loading of the joints and tissues.

This could increase injury risk. When exactly this breakdown happens, and to what extent this increases injury risk, though, is likely dependent on the individual runner.

Given all this information, it is not abundantly clear that a 3+ hour long run would increase injury risk in every runner. What is clear is that runners with extensive injury history should probably not do long runs greater than 3 hours, and that runners should never rapidly increase long run duration (i.e. the “too much, too soon” theory). In addition, runners might want to cut down their long run duration if they notice a breakdown in form occurring.

TLDR: The time until form breakdown and possibly increased injury risk likely varies based on the individual runner.

Problems with the 3 hour rule

My biggest issue with the 3 hour rule – as a coach and an athlete – is the simple fact that it ignores the individualization that should go into a well-thought-out training plan. It also ignores the rest of the plan, placing excess emphasis on the one individual run.

If we’re thinking about a 4-hour marathoner training 5x/week, then sure – the 3-hour rule holds up just fine.

But let’s say we’re talking about a slower runner – someone that can comfortably run 13-minute miles on longer runs – with no prior injury history. If they’re training for a marathon and use the 3-hour cut off, that means their very longest run would max out at 13.8 miles. I wouldn’t feel confident that a 14-mile run would successfully prepare that athlete to conquer a 26.2-mile run.

Would I recommend that athlete tackle a 20 miler that would put them on the road for over 4:15? Probably not. But might they work up to a 3:30-3:45 long run of around 16-17 miles? I don’t think that’s unreasonable. It would give the athlete the mental boost of knowing they can make it that far, and straddles the line between injury risk and physical/psychological capacity.

The 3+ rule also fundamentally ignores many ultra runners, who are naturally going to do long, relatively slow runs on a trail to prepare themselves for races. For example, a runner preparing for a 12-hour ultra will almost certainly end up having some runs in their training plan that exceed 3 hours. Of course, with much of ultra training, the bread and butter is in back-to-back long runs, but there will still likely be 3+ hour long runs sometimes in a training plan.

So should you run longer than 3 hours?

Like most information in the nutrition and fitness world: it depends.

Whomp, whomp. I know, no one likes that answer. But it does!

Here are some questions I’d ask as a coach – or that you can ask yourself! – when determining how long to make your longest runs. Keep in mind each question should not be analyzed in a silo; all of these should be assessed together to determine the best way to structure a training plan:

• What are you training for? There’s going to be a big difference in long run time for athlete training for a road marathon compared to an athlete training for a 24-hour trail ultra. That ultra-athlete will want more time on feet and longer runs to practice with gear and fueling.

• What is your easy run pace? If someone wants to do their first marathon, is running 12-minute miles with a low percentage of max heart rate on long runs, and bounces back quickly – there may not be a big issue in tackling an 18 miler that would put them around 3:30 as their max time.

• Are you using run-walk intervals? That break from running mechanics can give you extra time on feet and extend your long run more safely (IMO) compared to straight running.

• Do you have prior running injuries, especially in the last 12 months? If so, you should be more conservative with long run distance given the prior injury compared to someone without that history.

• Are you adequately fueling on a long run? Skimping on fuel can lead to increased muscle breakdown, which could affect recovery time. I would probably be more conservative on long run duration with an athlete that is dead set on fasted runs, for example, versus an athlete who fuels well on long runs.

• Are you adequately fueling in everyday life? RED-S (relatively energy deficiency in sport) can occur when an athlete isn’t eating enough to support both their everyday needs and their training needs. It can cause numerous health problems, including increased injury risk. Athletes struggling with this may need to pull back on duration.

• What terrain are you running on? Road miles generally lead to more wear-and-tear on the body than easy trail miles. A hilly run will take more out of you than a flat run. You’ll want to think about these (both in the context of training and your race) when determining long run distance.

• What is the weather like? A 90-degree day is certainly not the time to be pushing the long run too far.

• What is your data or subjective feedback showing us? If long runs appear to be too intense (as evidenced by excessively high heart rates, high RPE, or poor recovery), that is a sign that the intensity and/or duration should be pulled back.

• What is your overall training plan? Was there an ample running base built before entering this training season? Is there a gradual progression of mileage with regular drop-down weeks for recovery? If so, occasional runs slightly over 3 hours (assuming no injury risk) may not be problematic. On the flip side, an athlete that has missed multiple runs in a training cycle will need to be more conservative.

• Do you feel you need the psychological boost? Some athletes want to get as close to race-day numbers as possible to feel like they can do it. If the difference between a 16 miler and an 18 miler is 3 hours versus 3:20 – but that 18 miler will give the athlete the mental boost they need – it may be fine. (Again, assuming some of the other factors mentioned above like injuries aren’t at play).

• Are you practicing good recovery strategies? Recovery is essential for overall success in training. For example, getting enough carbs and protein, getting enough sleep, and other recovery strategies may help you bounce back easier from long runs.

Lastly – consider the overall plan!

While the long run is a major part of training, it’s your total weekly volume and periodized plan that is likely far more important than any one individual long run duration.

Are you running enough mileage throughout the week? Are you running the right intensities for that mileage? Are you gradually building those long runs up, with ample drop down weeks for recovery? All of this needs to be looked at in its entirety.

In many plans, long runs can be a bit shorter, provided the overall training volume and intensity is sufficient. For example, a tough run on a Thursday, an easy run on a Friday, and a 2-hour long run on a Saturday can be very effective for teaching the body to run long on legs that aren’t 100% fresh. This can simulate the fatigue of race day while still lessening practical injury risk.

The Bottom Line

While the 3-hour rule is tossed around as being based on research, the actual research is quite muddy. Yes, there are likely diminishing returns for running after a certain point. Yes, there is likely increased injury risk for runners after a certain point. But where these cut-offs exist are not clear in the research and likely depend on the individual runner.

There should always be a cost-benefit analysis considering the factors above when deciding whether to include a long run of over 3 hours in a training plan. Runners with past injuries or poor fueling practices should be more conservative with long run time. Runners who recovery quickly and have low injury risk may be fine to include some occasional runs over 3 hours.

Above all, the overall training plan should be well structured with very gradual increases in volume and intensity – regardless of what the long run distance is.

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