Imagine you’re in the thick of marathon training and your 30K falls on the weekend you’re going to be on vacation with your family. You have a 9am tour planned, so you figure you can get in a solid 20K beforehand, then log the remaining 10K that afternoon when you get back to your hotel.

Or, maybe you have a small injury that starts bugging you around 20 kilometres in, so you call it at 20, then log the remaining 10K later that day when you are feeling better.

Splitting up your long run within the same day is pretty much the same thing as logging continuous miles, right? Not so fast.

“The whole point of a long run is to get your body used to being on your feet for hours at a time, and that’s something that your body has to adapt to,” says Kara Dudley, an RRCA-certified run coach and founder of Rerouted Running. The good news is that slowing to a walk for a few seconds or minutes during a long run is totally okay. But this also means you’re doing yourself a disservice if you try to split your long run up throughout the day.

Meg Takacs, CPT, a UESCA-certified run coach and founder of the Movement and Miles app, agrees that conquering the long run in one continuous go is important. “It’s going to be different physiologically if you do the 30K straight than it would be if you did 15K in the morning and 15K in the afternoon,” she says. “With marathon training, what matters most is not so much pace or mileage, but more so time on your feet, and that allows you to practice nutrition and hydration,” she adds.

Long runs allow you to “approach race day with an idea of what your body’s going to be able to handle, or not…

These long-duration runs can also expose potential weaknesses, like an IT band issue that pops up two hours in, that wouldn’t be apparent in two shorter runs, Takacs says. Long runs allow you to “approach race day with a more knowledgeable idea of what your body’s going to be able to handle, or not,” she adds.

What’s more, your muscles might stiffen up between runs, putting you at greater risk of injury on the second run, Dudley says.

All of this said, sometimes you might need a less conventional approach to the long run. Here, Dudley and Takacs share some alternatives to consider before splitting it up.

4 Ways to Tackle Your Long Run When You Can’t Conquer All the Miles

1. If you’re a beginner or run/walker… go by time rather than mileage.
Dudley believes that, in general, three hours is sufficient time on your feet to prep for a marathon and can be a better goal than going for, say, 30 or 32K, which may take even longer to cover. One of Dudley’s clients who ran the New York City Marathon never went over 20K in her training, but logged several three-hour runs to get that time on her feet.

2. If you can’t squeeze in your long run one week… swap it.
“A lot of people see marathon plans that are slow builds over time [where] you’re doing 25, then 26, then 28, then 30 kilometres,” says Dudley. “But it doesn’t have to be like that.”

Instead of splitting your long run, you can work around frequent travel and/or time constraints to identify the ideal weekends for your most important miles. That may look more like doing 30K, then 16, then 20, then another 30, for example. “It doesn’t have to necessarily be that progression that we all think of when it comes to marathon training,” she underscores.

Takacs agrees that it’s safe to shift days around in your training plan, which could also happen within the week. There’s no rule that your long run has to happen over a weekend, after all! If you have more time during the week, swap that day’s workout for your long run; just make sure you sandwich it with an easy run or rest day, rather than a speed workout.

If there’s a week or two that it’s truly not possible to get in your long run in one go, Dudley believes you’d be better off just going as long as you can in one run, rather than trying to tack on additional potentially junky miles later in the day. Keep in mind that missing one long run isn’t going to derail your training cycle.

3. If you have aches and pains… finish on the bike.
As always, see your doctor or physical therapist if you’re dealing with pain or an injury for personalised advice. So long as you have the all-clear and you’re dealing with something that comes and goes and tends to flare up only after you reach a certain mileage, Dudley has a suggested workaround for you: Log as many miles as you can, then jump on the bike to finish out the rest of the time that would have been in that run.

For example, if you run 6-minute kilometres and were supposed to run a 30K, but start to feel achy at 20, you’d be on the bike for 50 minutes after your run. Rather than splitting your long run, this strategy still gets you the aerobic benefit of being out there for longer, Dudley says.

“These types of accommodations generally may be for injury-prone people who don’t respond well to high mileage or are coming back from a bone stress injury,” Dudley says.

4. If you have a chronic injury or truly no time… reassess your goal race.
Now, it’s important to differentiate between an injury that temporarily sidelines you and something chronic that means you should reconsider the marathon altogether. Seeing a physical therapist or doctor is always the best choice in these situations, but Takacs emphasises that “if you’re avoiding the long run because your body can’t handle it, then I wouldn’t recommend [you] do an actual marathon.”

Maybe you reassess, get some good PT, and sign up for a marathon the following season instead.

The same goes for people who just don’t have the time to commit to marathon training. If you find that week after week you need to split up your long runs, this may not be the right moment to be marathon training. Full stop.

A Few Exceptions to the Rule of Not Splitting Up Your Long Run
Now, there are always outliers, and Takacs says that if you’ve been splitting up your long runs during marathon training and you’re finishing your races injury-free and happy with your times, more power to you. “If that works for someone, do what works,” she says.

Dudley adds that she might prescribe 15K in the morning and 15 at night (for example) to her more advanced marathoners if there was a reason to do so. “One of those reasons might be if they’re preparing for an ultramarathon or a relay where they’re going to be running every few hours. Splitting up the long run would help to stimulate that back-to-back fatigue they’re likely to experience,” she says.

One more thing: If you want to split up other easy runs within your week (say, a midweek easy 10K two 5K runs), that would likely have less of a negative effect than splitting up your weekly long run, Takacs says. That’s because you’ll still accumulate weekly mileage and time on your feet, without taking away the advantages you gain from your weekend long run when you want to practice going extra long like you will on race day.

This article first appeared on Runner’s World USA.

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