Spoiler alert: It’s usually not even close to 21.1 kilometres.
In half marathon training, the long run gets a lot of attention because it’s the closest you’ll get to race-specific mileage. With that in mind, it’s easy to think you need to put most of your focus on increasing your long run distance to make that eventual 21.1 kilometre race feel easier.
But physiologically, that approach doesn’t quite track. “One long run per week can’t compensate for low overall volume because the body adapts better to frequent exposure to running stress,” Justine Williams Roper, PT, DPT, RRCA-certified run coach and founder of InHer Physique Pelvic Therapy and Wellness, previously told Runner’s World. Essentially, your long runs are only as good as the rest of your training volume.
Runners with a less-is-more mindset or those with hectic schedules, rejoice! Your longest long run doesn’t have to be as long as you may think, or even approach the half-marathon distance. This guide outlines how far you can run at a minimum on your longest run as you train to race your next half.
Why Your Long Runs Should Have a Limit
Before getting into specific mileage, there’s one guideline that keeps your training balanced: Your long run should make up no more than 50 percent of your weekly mileage.
Half marathon fitness is built through consistency, not a single standout effort. The shorter runs in your plan help build up your connective tissues, joints, and ligaments. If your long run takes up too much of your mileage, it could lead to an overuse injury or increased recovery time, which comes at the expense of those important easy runs. Regardless of the exact consequence, extending your long runs too long can backfire.
Beginner Runners: Aim for 12 Kilometres Minimum
If you’re training for your first half or are still new to the sport, you can get away with a minimum long run distance that is considerably shorter than your race distance, but still has the ability to boost your aerobic fitness.
For most beginners who run three or four times per week, a long run in the 12- to 16-kilometrerange is a solid baseline. (While you can get away with 12, 16 is often a sweet spot for runners in terms of boosting physical capabilities and mental confidence.)
When paired with a weekly mileage total of about 32 kilometres, long runs in this range fit under that 50 percent guideline. More importantly, it also allows you to run consistently throughout the week without burning too much energy on one high-mileage effort.
The length of your training plan matters, too. For beginners, coaches recommend as much as 16 to 20 weeks of prep time to establish consistency and build fitness. “You have to respect the distance and your individual recovery while putting in the miles,” Lea Genders, an RRCA-certified run coach and NASM-certified personal trainer, previously told Runner’s World.
The longer the plan, the more time you have to gradually build up both your weekly mileage and your long run distance.
Experienced Runners: 17 Kilometres Will (Usually) Do the Job
Runners with more half marathon experience and faster time goals should stretch their minimums just a bit while staying proportionate to higher-mileage weeks.
Seasoned recreational half-marathoners (basically anyone who’s done a couple 21.1-kilometres before) who are clocking 40 kilometres a week and have a time goal should set their long run minimum at 17 kilometres. Those who run regularly and may not have an ambitious time goal can get away with running less (more in that 12 to 16 kilometre range), Roper said. Either way, you still want to include a bit of higher-intensity race-pace running in these shorter long runs.
Runners with higher weekly mileage and PR goals should increase their minimum long run distance proportionally to their overall mileage while staying within the 50 percent guideline. For example, you might aim for a 22-kilometre long run when clocking a total of 48 kilometres weekly. Going longer than the race distance, in this case, can have additional aerobic benefits, helping you perform even better on race day.
