Do you want to slow the passage of time? Give the 15/15 Challenge a try. 15 minutes may not sound like a long time under most circumstances, but it’s an eternity when you’re running at maximum effort on a treadmill set to 15% incline. The 15/15 Challenge is a brutal, yet effective benchmark test that trail and obstacle course racing (OCR) athletes use to see where their fitness lies. In the OCR world, this test happens to mimic the start of a Spartan sprint or super–on a steep hill, and at a blistering pace.

Further popularizing this trial of mental and physical grit, in 2005, Trail Runner Magazine began hosting live, head-to-head 15/15 treadmill challenges featuring some of the biggest names in the sport such as Sage Canaday, Max King, Jeff Browning, Cynthia Fowler, and Larisa Dannis. In 2014, when Sage Canaday and Max King went head-to-head in the 15/15 uphill treadmill challenge, Canaday ran a mind-blowing 1.92 miles and King banked 1.73 miles. 

There are plenty of fitness tests out there, but 15 minutes at 15% incline on the treadmill is a particular kind of pain. It demands runners to be both strong and aerobically fit–two traits we see most often in successful OCR athletes and trail runners. A sub-15-minute 5k runner might be able to throw down a respectable time on this test, but without some serious leg strength, they might not measure up against a slightly slower 5k runner with mountain chops. 

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Want to see how you stack up? Let’s dive into the 15/15  treadmill challenge! We’ll cover the what, why, when, and how of the challenge plus another fitness test that can support you in reaching your OCR and trail running goals!

What is the 15/15 Challenge?

In short, the 15/15 Challenge is simply testing how far an athlete can run in 15 minutes at 15% incline on a treadmill. While 15 might seem like an arbitrary number, there’s a purpose to the duration and incline of this challenge.

15 Minutes: short enough to test a runner’s top end (VO2 Max, which is the maximum rate of oxygen consumption during high intensity exercise), but long enough to also be an endurance challenge. On average, runners can hold their VO2 max effort for around 3-8 minutes. With a 15-minute challenge, runners must also be efficient at clearing lactate and aware of their pacing.

15% Incline: 15% incline is steep! 1 mile of a 15% grade climbs 792 vertical feet. Steeper inclines require runners to have leg strength and endurance beyond the running economy (how efficiently a runner uses energy while running–better running economy means that you’ll use less oxygen for a given pace) that flat terrain demands. Additionally, 15% incline is accessible to most runners. If you walk into any commercial gym setting, hop on a treadmill, and toggle the incline up to its maximum, most likely, you’ll find that standard treadmills don’t get any steeper than 15%. 

The 15/15 Challenge has grown in popularity among OCR and trail athletes because it is a standardized, repeatable fitness metric that allows for clear comparison to oneself and other athletes.

The grueling nature of a steep, unrelenting climb also tests an athlete’s mental toughness–an attribute that endurance athletes need to be successful. Plus, it’s specific to the fast and furious uphill starts of the gnarly mountain races we know and love.

The 15/15 Treadmill Challenge Protocol

1. Warm up: for short, high intensity efforts, the warm up is important! As a general rule, the shorter the event, the longer the warmup should be. Warmups should aim to target the heart rate and effort zones that you’re going to perform at during the challenge. 

If you haven’t spent time running uphill on a steep grade for a long period of time before, consider doing some easy uphill running at 10-15% incline in separate training sessions before doing the 15/15 challenge to avoid injury. If you have a recent history of a calf or Achilles injury, this might not be the best challenge for you. 

Example warmup: Run at an easy effort for 15-30 minutes, then begin gradually ramping up the effort for 3-5 minutes until you’re breathing hard and break a sweat. You can throw in a few strides (short 15-30s accelerations) during this ramp up. Stop running and then perform any pre-workout drills or dynamic movements you use on a regular basis. 

2. Set up: after you’ve warmed up, hydrate and get ready to run! The treadmill setup is simple–program it for 15 minutes, set the incline to 15%, select a slower starting speed, and hit “start”. Begin accelerating the treadmill speed until you reach a setting that is challenging, but one you anticipate being able to hold for the 15 minutes. 

Pacing tip: when you begin running, try to choose a speed that feels just a tad too easy. It’s better to increase the treadmill speed as the challenge goes on than to have to slow down dramatically because you went out too hard. If that isn’t your style, you can also choose a speed that you think you’ll be able to hold for the 15 minutes and try to hang on.

For reference, here are some grade-adjusted paces (GAP) for 15% incline. GAP refers to the pace equivalent you might run on a flat surface. GAP is a model with limitations, but it helps us understand effort on steeper inclines. While apps like Strava and Garmin Connect list GAP paces, they are using a proprietary method for calculation. RunBundle provides a free online GAP calculator if you’d like to explore more

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3. During the challenge: lean into the uphill and allow your posterior chain to propel you up that “hill”! Try to remember to relax your upper body to minimize wasted energy. A helpful cue for some runners is to make sure your shoulders aren’t creeping up towards your ears. If music or running hype videos are your go-to for treadmill workouts, use them as tools to motivate you and keep you focused on the effort.

4. Cooldown: Once your 15 minutes is up, either manually stop the treadmill or allow the treadmill to slow on its own if you preset the session time. Record your total distance run during the 15 minutes! Revel in your accomplishment as you jog at an easy effort for 5-15 minutes to cooldown. Follow your normal post-workout routine.

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Once you’re ready to use your data collected from the 15/15 challenge, you can refer to these benchmarks as potential indicators of race readiness. Keep in mind that these numbers are not hard and fast rules (or scientifically sourced)–they are merely suggestions based on other runners’ results to help gauge uphill fitness. This of course comes with the strong disclaimer that there are no guarantees in trail and OCR! You’ll still need to have downhill skill, and, in the case of OCR, obstacle proficiency.

Keep in mind that the women’s chart is simply a modified version of the men’s to account for the average finish time differences across genders. On average, female athletes finish within 10-20% of their male counterparts.

How to Use the 15/15 Challenge as a Tool in Training

The 15/15 uphill treadmill challenge is no easy feat, but it’s a useful fitness benchmark as well as a fun (some might argue with the usage of the term) workout that you can repeat during a training block; the trick is knowing when to use it and for which events! 

The when:

In terms of timing your 15/15 uphill treadmill challenge, it’s useful to do at the beginning of a training block so that you have a baseline metric to gauge your fitness progression over time. 

If you keep a training log, take notes on what treadmill speeds you use, and when you increased or decreased your speed. Even if you re-test and run the exact same distance, you might notice that you didn’t need to slow down and you ran a steadier pace the second time around. 

10-14 days prior to your goal event, and at least 4-5 weeks after your initial test, you can do a second test to see where your fitness stands! Avoid doing the 15/15 challenge during your taper for longer events. 

Generally, try not to overdo these high intensity bouts. During a training block, you won’t want to exceed repeating this test more than 2 times.

Which Events:

For trail and OCR athletes competing in short and spicy sub-ultra races, the 15 minutes at 15% is helpful to gauge high intensity output, aerobic fitness, and strength. 

If you’re competing in longer trail races and ultras, the 60 minute maximum vert test might also be helpful. This is because an athlete’s staying power and lactate threshold are even more important in longer events. Plus, a longer test also requires smarter pacing–a valuable attribute in racing. 

The 60-Minute Max Vert Test

• Similar to the 15/15 challenge, the 60-minute max vert test requires a treadmill that can be set to 15% incline. 
• Instead of only running for 15 minutes, you run (and possibly hike) for 60 minutes at 15%
• If your treadmill doesn’t track vert, you can use this calculator to find the total vertical feet traveled over the hour by simply plugging in your distance and treadmill incline.

The 15/15 Uphill Treadmill Challenge in a Nutshell

• 15 minutes at 15% incline–how far can you run?
• For male athletes, being able to run 1 mile or more is a great benchmark for the fitness needed to have an enjoyable race. For female athletes, 0.8 miles.
• Being able to run 1.8 or more miles as a male athlete is considered elite. For females, 1.44 miles or more.
• The 15/15 Challenge requires athletes to have both aerobic fitness and leg strength
• 15% for 15 minutes is an intense VO2 max stimulus that shouldn’t be used more than a couple of times in a training block.
• Your results for the 15/15 Challenge don’t guarantee a level of performance at a race. You’ll also need trail skill and, in the case of OCR, obstacle proficiency! 

How far do you think you can run on a treadmill in 15 minutes at 15% incline?

Try the 15/15 treadmill challenge and find out how you stack up! If you’ve already done the 15/15 challenge, try it again and see how your fitness has progressed!