How to Train For A 50K

Written by:

Jim Rutberg

CTS Pro Endurance Coach

Updated On

May 8, 2025

(Written with guidance from CTS Ultrarunning Coach Cliff Pittman)

Endurance runners like a challenge, which is why there is a progression of competition distances that starts with five kilometers and goes all the way to multi-day ultramarathons. Runners who conquer the road marathon often look to the trail 50K as the introductory distance for ultrarunning. A 26.2-mile marathon is 42.2 kilometers, so on paper a 50K is only about eight more kilometers (five miles). If you successfully prepared to run 42 kilometers, how hard could it be to run another eight?! As it turns out, this is exactly the thinking that gets first-time 50K runners into trouble. 

Road Marathons vs. Trail 50K Races

The roughly 8-kilometer difference between a road marathon and a trail 50K is deceptive. To run a road 50K, for instance, a fit marathoner could adjust their pace and complete the distance. That’s because the determinants of performance for a road marathon are well established. For instance, if you know an athlete’s VO2max, the fraction of VO2max they can sustain (e.g., 90% fractional utilization), and their running economy (milliliters of oxygen consumed to maintain a given pace), you can predict their fastest marathon time with reasonable accuracy. 

The unpredictability of trail 50K finishing times is due to the immense variability runners encounter during events. Some of these variables are highlighted in the table below. Fitness and running economy are still important, and runners with higher VO2max values and better running economy will still go faster, but finishing times for all runners are slower (compared to a road marathon or road 50k) because of mixed surfaces, steep uphills and downhills, and technical trail segments. And although both road and trail events are run in varying weather conditions, trail 50Ks are often held in more remote locations, sometimes at altitude (elevations above 2000 meters), or places that deliberately feature extreme conditions (e.g., deserts, rugged canyons, etc.).     

Why a Trail 50K is Harder Than a Road Marathon

The extra distance isn’t what makes a trail 50K significantly harder than a road marathon, or even a road 50K. It’s all the other extras that make the difference:

• Extra time on course: Being on course longer means more time and opportunities for things to go wrong or for mistakes to catch up to you. In shorter events, athletes can significantly dehydrate during their races but reach the finish line before suffering serious consequences. Hydration errors in 6-8 hour trail 50K events can be unrecoverable. 
• Extra exposure to weather: A three-hour marathon that starts at 7:00AM means exposure to the rising sun and increasing temperatures for three hours. Even if the weather is bad, it’s only three hours of rain, wind, etc. When you double that exposure to the elements there are more chances for significant weather changes and it becomes harder for athletes to regulate and manage core temperature. 
• Extra fuel required: Athletes perform best during endurance sports when they steadily consume both calories (mostly from carbohydrate) and fluids (mostly water). The hourly consumption of fluid and calories can change with temperature and pace/intensity, but a runner must consume more of both during a 6-8 hour trail 50K compared to a marathon. This increases the risk or likelihood of gastric distress, which is one of the leading reasons runners fail to finish races. 
• Extra muscle damage: Distance runners incur muscle damage with every eccentric muscle contraction (i.e., muscle under tension while lengthening). Trail 50K races and any race with significant downhill running will induce greater muscle damage than a predominantly flat race. This is somewhat balanced by the increased impact forces runners experience during road marathons on hard pavement, and in both instances, the extent of muscle damage depends on a runner’s pacing decisions. Decreasing pace on trail descents or flat pavement can help manage muscle damage. Running harder in either condition will dramatically increase muscle damage. 
• Extra mental fortitude: Running a road marathon takes a lot of mental fortitude and resilience. To run 1.5 – 2x the amount of time means 1.5 – 2x longer to stay focused, make good decisions on pacing and fueling and clothing and where you put your foot on the next stride. It’s more time you have to fight against the urge to quit, particularly as the reasons you want to quit (see above) start to add up.  

How to Train for a 50K

The predictability of road marathon performance makes marathon training simple to prescribe. That doesn’t mean marathon training is easy! It just means we know how to design training programs to prepare athletes for the predictable demands of those events. That’s why free marathon training plans are handed out like takeout lunch menus. And there’s nothing wrong with that. They’re good plans and make marathons more accessible to more runners, which benefits everyone! Static (or even AI-adjusted) training plans for 50K trail races are frequently less effective than marathon programs because they struggle to address the extras mentioned above. 

Training for a successful trail 50K is all about preparing for all the extras. Here’s how you can do that.

Training for Extra Time on Course

This is where long runs come in handy, not just in terms of mileage, but time-on-feet. Most of your fitness-related training runs will be 1-2 hours in duration. These are the weekday aerobic endurance runs and 1-2 interval workouts per week. Longer runs might start out at 2 hours and progress to 4 and 5 hours, but you don’t need to do these weekly. They’re too hard on the body to do too frequently. Rather, schedule these purposely long runs every few weeks and make them gradually longer as your training progresses. These will not be fast. They are less about building fitness and more about creating good pacing, hydration, fueling, and gear habits.

Throughout your 50K training, develop a problem-solving mindset. Trail ultramarathons require more self-reliance than highly-supported road marathons. Rehearse “if/then” scenarios about what you’ll do if your stomach turns, if you go off-course, if you develop a blister, if you run out of water before the next aid station, etc.

Training for Extra Exposure to Weather

The first thing to do is deliberately train in all types of weather. Stop waiting for sunny days and training indoors when it’s cold or hot. Not only do trail runners need to develop the resilience to run in less-than-ideal conditions, but you also need to learn how your body (and mind/attitude) responds to the cold or rain or heat. This shouldn’t be a last-minute priority. You can start being an all-weather runner (except obviously dangerous weather…) at any point, but if you’re currently a fair-weather runner, you definitely want to shift to all-weather running at least 8-12 weeks out from your trail 50K.

Having and knowing how to use the appropriate gear is key to being an all-weather runner. Learn to layer and train with removable, stowable layers like a light wind shell or arm sleeves. Carrying this gear in a hydration vest will also help you adapt to the feeling of running with some additional weight. This is important because you’ll most likely run with a similar pack and gear during your event.

Training for Extra Fueling

Fueling and hydration strategies for ultramarathon are huge topics, but the basics are the same as you utilized for marathon training and competitions. You need a steady supply of calories (mostly carbohydrate) and fluid (mostly water) to spare muscle glycogen and directly fuel working muscles. The standard recommendations still call for a starting point of 40-60 grams of carbohydrate per hour, 20-40 ounces of water per hour (to be scaled up in hot conditions), along with 500-700mg of sodium per liter of fluid consumed. Newer recommendations encourage carbohydrate intakes of 75-90 grams per hour or even higher, but these amounts can cause stomach upset if athletes do not gradually work up to them. “Gut training” helps you adapt to consuming not only more fluid and more calories per hour, but also to consuming these higher volumes of food and fluid hour after hour. 

Start by determining the food and fluid intakes you are currently comfortable with (note: these will be condition-specific, based on intensity/pace and temperature). The result will likely be less than you think, and many runners may find they barely reach 40-50 grams/hour currently. Over a period of weeks, gradually add carbohydrates by going up to 60 grams, then 75, then 90 grams/hour during long runs. Pay attention to how your long runs feel, as well as how your gut feels. More isn’t always better. You’re looking for the range that helps you run well and feel good.

Keep in mind, the shape of the carbohydrates doesn’t matter. Recent research shows that rates of carbohydrate digestion are equal for fluid, gummy, or solid carbohydrate supplements (e.g., sports drinks, chews, and bars). Establish the foods and drinks that work best for you and alternate among them to keep your palate from fatiguing. A good approach during races is to use sports nutrition products as your baseline carbohydrate intake needs and then eat real foods at aid stations to address satiety. This becomes increasingly important as race duration increases.  

Training to Mitigate Extra Muscle Damage

Eccentric loading in training is a way to mitigate or at least slow down the accumulation of muscle damage from running downhill during a trail 50K. The important thing to remember is that “a little goes a long way”. It doesn’t take much downhill run training to achieve the desired adaptation. Long runs with elevation change that closely matches your race can help condition the quadriceps. Avoid hard downhill intervals because the risks far outweigh any potential reward. 

Strength training can also help. Focus on eccentric strength movements (e.g., split squats, step-downs, and single-leg RDLs). CTS Coach Cliff Pittman, a Certified Personal Trainer with the National Academy of Sports Medicine (NASM-CPT), advises, “Strength training should always support your run performance, not compete with it. Too much strength work, especially during peak run volume, can lead to excessive fatigue and interfere with recovery. Apply the minimum effective dose: typically two short sessions per week. For optimal sequencing, strength work should align with your harder run days: Run first, lift second. That way, recovery days can be fully restorative.”

Training for Extra Mental Fortitude

There’s an adage in ultradistance sports that says no matter how great or terrible you feel right now, it won’t last forever. The best ultramarathon runners are able to stay present, take advantage of the good times, and acknowledge and redirect negative thoughts in the bad times. Discomfort and negative thoughts are inevitable but you can choose and control your responses to them. And that’s easy to say when you’re well rested and sitting in your living room, but the place to practice and learn how to accept discomfort and redirect negative thoughts is during your long training runs.

Creating a strong personal connection to the reason you’re running (your “why) can also keep you in the race or help you stick to your training program when the going gets hard. Coach Pittman told me, “Values provide direction when motivation fades.” When you connect your running to your personal values (e.g., resilience, growth, adventure, etc.), you’re digging an even deeper well to draw from during your toughest moments.