How to Go the Distance: Building Run Endurance

As an experienced run coach, I’ve seen countless runners set ambitious goals, from completing their first 5k to racing marathons and ultra-distance events. 

The foundation of these achievements is base endurance or what some might call run fitness – the ability to sustain prolonged physical effort more efficiently over all distances. 

Building endurance is not just about running more; it’s an intentional blend of training, recovery, nutrition, and mental strength. And as my first endurance coach said, “There are no shortcuts to building endurance, and the process will not be rushed.”

Start with a Solid Base

Endurance building takes time, as my first coach pointed out. Begin with establishing base mileage, which involves consistent, low-intensity runs (Rated Perceived Excertion 2-3; see image below). 

Start modestly, with distances and an effort that feel comfortable. Gradually increase your weekly mileage by no more than 10% to prevent injury and build momentum. Consistency is critical during this time.

Remember that each step builds a stronger foundation, even on days when you may not feel like running. 

Incorporate Interval Training

Once you feel comfortable that you have a solid base, it’s time to introduce variety into your runs. Interval training – alternating high and low-intensity periods – can improve cardiovascular efficiency and increase lactate threshold.

This means you’ll run faster and longer before fatigue sets in. Start with shorter intervals, like 1-2 minutes, then try incorporating intervals such as 400 or 800-meter repeats at a pace faster than your typical run, followed by an equal or longer recovery jog. 

Then, you can move to additional or longer intervals closer to your 5k pace or an RPE of 8-9.

Long Runs: The Foundation of Endurance

Weekly long runs are non-negotiable. Especially if you are training for a longer event like a half or full marathon. Long runs are considered “key workouts” and should not be missed if at all possible.

Long runs help prepare your body for an extended effort, teaching your muscles to utilize energy more efficiently. Shoot for a long run every 7–10 days, extending the distance incrementally.

Though the distance of your longest run of the week will vary depending on your goals and experience, we generally like to see it no more than 20-30% of your total weekly mileage. Remember to pace yourself; these runs are time on your feet, not pace or speed.

Consider Frequency for Durability

While I know people who have qualified for the Boston Marathon only running three days a week, I would not advise this approach. Another goal in running is building run durability and fatigue resistance.

Running more frequently throughout the week versus trying to jam mileage in on only 3-4 days can be risky – especially for less experienced runners.

Try to run a minimum of 4 days a week spread out to give you time to recover between more intense and longer sessions.

Then, as you progress, add one or two additional runs every other week or so to give you some extra time on your feet to build durability.

These runs should feel very easy and no more than 20 minutes each. You can even do these “frequency runs” on a day you do cross-training like cycling or swimming.  

Cross-Training Can be Helpful

Running isn’t the only way to boost your endurance. Cross-training activities like cycling, swimming, or rowing enhance cardiovascular strength while giving you an opportunity for active recovery.

Incorporating strength training, particularly for your core and legs, can help build durability and prevent injury. 

Fueling

Fueling during your workouts and races is as important as anything else. Your body needs the right mix of carbohydrates, proteins, and fats to perform and recover.

Prioritize complex carbs for sustained energy, lean proteins for muscle repair, and healthy fats for longer-lasting fuel. Hydration and electrolyte intake are equally important; ensure you’re well-hydrated before, during, and after runs.

Rest and Recovery

Coaches often tell their athletes that it isn’t so much the runs that make us stronger but the recovery in between. And it’s true. Not just complete rest days but also the little opportunities in between runs that help us recover and reset.

Your endurance gains are made during recovery as your muscles repair and adapt to training stresses. This is probably the hardest thing for aspiring runners to understand. Schedule regular full rest days, and consider a down week every 3–5 weeks where you decrease the overall training load to allow deeper and lasting recovery.

Listen to Your Body

Lastly, always listen to your body. I know everyone says this, but it is an important part of being a runner. Recognize the difference between discomfort, which signals growth, and pain, which signals harm or injury. If something doesn’t feel right, take an extra rest day.

Building running endurance doesn’t happen overnight. It requires patience and the right kind and amount of work. Understanding it’s a journey and not just about the miles will help provide a solid foundation to make running a part of your life for a long time. 

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