An expert- and science-backed guide to finishing just as strong as you started.
BY ELIZABETH MILLARD MEDICALLY REVIEWED BY JOHN VASUDEVAN, M.D.
You know when your body starts to fatigue during a run or strength workout. Every single step or rep feels sooo difficult that your mind starts to doubt whether you’ll make it through.
Dealing with this kind of fatigue is common, and it can tank performance or even set you up for injury. For example, slogging through the second half of a marathon even though you feel wiped out can affect your form and gait.
Although there are some quick fixes, like energy gels and drinks that provide a temporary boost of energy (you need carbs to fight off fatigue after all!), there’s a science-backed approach to making your energy last longer—and that’s building fatigue resistance.
This doesn’t mean learning to push through the weariness when it comes. Instead, it’s a focus on training in a way that prevents those waves from crashing in the first place. Here’s what you need to know.
Exactly What Fatigue Resistance Means
Although the terms fatigue and tiredness tend to get used interchangeably, there’s a crucial difference between them, and it’s important know that difference when it comes to developing more fatigue resistance, according to Sandra Hunter, Ph.D., director of the Athletic and Human Performance Research Center at Marquette University.
Overall, tiredness is a temporary condition that affects your body in a general way, she tells Runner’s World. For example, if you didn’t sleep well the night before.
There’s also a type of fatigue that’s considered a symptom of medical conditions. For example, cancer or multiple sclerosis often involve fatigue as a symptom and side effect of these conditions. This type of fatigue affects several parts of the body, as well as the brain.
When talking about fatigue with an activity like running, that falls under a category called exercise-induced fatigue, Hunter says.
“One way to tell if you’re dealing with exercise-induced fatigue instead of tiredness is that this fatigue is acute, it can resolve within minutes in some cases, or hours, depending on what’s happening on a muscular level,” Hunter adds. “You would not have this for days.”
In other words, even though you might feel body-wide effects like weakness or heavy legs, exercise-induced fatigue is tied to muscular changes that occur during activity.
“When speaking in terms of muscular capacity during exercise, fatigue is an involuntary decrease in the muscles’ ability to produce force or produce a powerful contraction,” Sonia DelBusso, D.P.T., doctor of physical therapy and corrective exercise specialist at Providence Saint John’s Health Center in California, tells Runner’s World. “Fatigue is brought on by accumulation of lactate in the muscles. This influx of lactate causes a physiological inhibition of contraction capacity, leading to a reduction in exercise performance.”
Fatigue resistance tends to be genetically linked to your muscle fiber type, DelBusso adds. Individuals with a higher percentage of slow-twitch fibers tend to experience delayed onset of fatigue, compared to individuals with a higher percentage of fast-twitch fibers, who tend to be more apt with sprint-style running.
Although it would be helpful to determine which type of muscle fibers you’re genetically predisposed to relying on during your workouts, in some ways it doesn’t matter where you have that advantage, says DelBusso, because training in strategic ways can be a boon for building both types—and reducing the onset of fatigue as a result.
How do you do that? Experts offer key strategies.
5 Tools to Build Fatigue Resistance
1. Get in the Right Zone
Any runner would love to hear that with proper training, it’s possible to become completely fatigue resistant—if that were true, you could run an ultra every day—so it’s important to keep in mind that there is an upper limit for each individual, says DelBusso. But even modest improvements can make a difference in performance, and that begins with more time in the correct training zone.
“In order to improve your endurance and delay the onset of fatigue, incorporating zone 2 or low-intensity running, as well as interval training, is recommended,” she suggests. “Zone 2 running is done at a slow pace, in which you can comfortably carry on a conversation, and that allows you to run longer at a decreased workload.”
DelBusso says zone 2 training should feel easy—with a rate of perceived exertion, or RPE, of about 5 out of 10 or at about 60 to 70 percent of your max heart rate. For context, there are five heart rate zones for training, with zone 1 as the slowest and easiest pace, and zone 5 representing all-out effort that’s sustainable for only a very short amount of time, like 30 seconds. Zone 2 is just a step up from that low, recovery activity level.
While most smartwatches will help determine your heart rate zones and your zone 2 effort, the talk test is one of the best ways to make sure you stay within that zone (you should be able to talk to your running buddy!).
Training with more emphasis on zone 2 running allows for the gradual increase in total time spent running, DelBusso adds. For those who are training for longer runs, such as marathons, increasing the capacity of total running time is a crucial factor.
While training in zone 2 will build fatigue-resistant slow-twitch muscle fibers, it also allows for other benefits that stave off bonking in the later kilometres of a race, like a marathon. For example, aerobic workouts have been shown to increase the number of mitochondria—the powerhouse of our cells that help generate energy for our muscles to use during exercise. The better your mitochondria function, the more energy you’ll have for your runs.
While you need this zone 2 training, exercising in different zones is key for better fatigue resistance because you’ll build slow-twitch fibers in a lower zone and fast-twitch in a higher zone. “In order to recruit both types of muscle fibers, you have to train with a combination for high and low to become effective,” DelBusso says. “So these low-intensity workouts are key.” (More on that high zone in a minute!)
The ratio of your low- and high-intensity workouts will depend on factors like your training goals and how close you are to a race, she adds. But in general, the bulk of your fatigue-resistant training should be zone 2—for example, training three or four days a week in that zone and two days a week in a higher zone.
2. Add Intervals
Interval training can help increase power and contractility of both slow- and fast-twitch muscle fibers, says DelBusso. These workouts basically put the spring in your step.
According to the National Institutes of Health, efficient muscle contraction is important for several functions in the body, including better joint stability, temperature regulation, and posture. In running, contractility improvements can translate into the ability to exert greater force over a shorter period of time. This can make you faster, while also helping you fight fatigue when you pick up the pace.
“The combination of longer and slower runs, and faster, sprint workouts can help to train the muscles’ adaptability and combat the onset of fatigue,” DelBusso explains.
Research points to the best ways to make the most of your interval sessions. For example, a study published in the journal Kinesiology looked at different work-to-rest ratios for high-intensity interval training done with Taekwondo sessions and how that specifically played into fatigue resistance. The ratios assessed: 30 seconds work and 60 seconds rest; 30 seconds work and 120 seconds rest; and 30 seconds work and 240 seconds rest. After 10 sessions over four weeks, the most improvement in fatigue resistance came in the middle group with 120 seconds of rest. This HIIT sweet spot highlights the balance of high-intensity movement with rest periods—in other words, you need time to recover before going hard again.
In terms of why HIIT training works, a scientific review in the International Journal of Environmental Research and Public Health reports that it’s because this type of training produces numerous physiological adaptations that improve exercise capacity—and many of them lead to fatigue resistance. This includes a boost in aerobic endurance, maximal oxygen uptake (a.k.a. VO2 max), anaerobic capacity, and metabolic health, the researchers suggest.
Also, training at your lactate threshold during interval workouts can help you prolong the time it takes for lactate to accumulate, one of the markers of fatigue, which will help you last longer on the road.
While zone 2 running should be easy and enjoyable, your interval workouts should be uncomfortable, making it hard to push through to the end of the work period.
3. Mix in Lower-Body Strength Training
Because muscle fatigue can happen most in the lower body during a run—especially a long run like a marathon—strength work in these muscles is particularly important for reducing exercise-induced fatigue, Hunter says. In fact, research in the journal ERJ Open Research looking at more than 36,000 participants found that leg strength is a major contributor to exercise capacity, to the point where muscle weakness in the lower body should be assessed in patients who complain of fatigue and exercise intolerance.
Also, resistance training builds fast-twitch muscles fibers, as well as endurance capacity, muscular strength, and ability to produce force, according to research in the Scandinavian Journal of Medicine & Science in Sports. This all allows you to utilize your legs at a higher capacity on a run.
What’s more: “Strength training helps you isolate some of the muscles that provide stability, and those are the ones that get the most fatigued during a race, so building them up is helpful,” Hunter says. That includes prime movers like the quadriceps and hamstrings, but also core muscles and hip extensors, like the glutes.
Hunter’s favorite static move is a wall sit, which can fire up multiple stabilizer muscles, and also gives you a sense of progress based on time. For example, you may be able to do a wall sit for only 15 seconds when you start, but then work your way up to a minute and beyond over a series of weeks.
Dynamic strength exercises that can make a difference for fatigue resistance also include squats and calf raises, as well as bird dog and bridges. “These are useful not just for building more muscle, but they also give you greater body awareness so you can use your legs and arms more purposefully when you run,” says Hunter. “That can increase running efficiency, which is another variable for reducing exercise-induced fatigue.”
Basically, your body is similar to a machine, like a car or a home furnace: The more efficiently it runs, the less strain you’ll see on the overall system, extending how long it can operate well.
While Hunter says lifting lighter weights for higher reps will improve your fatigue resistance, you also need to lift for strength and power (heavier weights and lower reps)—particularly if you already have a strength base and need a greater challenge.
Finally, some research suggests that variable resistance devices—like resistance bands, some cable machines, and equipment like Tonal, which vary the load throughout a movement—may improve fatigue resistance more than traditional weight training.
With any method of lifting, the key is training to fatigue, in which the muscle group feels tired by the end of a set.
4. Focus on Recovery
As always, never skip your rest days. Hunter notes that recovery, when it comes to fatigue resistance, isn’t as researched as other aspects of exercise performance, but she believes it should be. “The better recovered you are, the faster you’ll be able to come back from exercise-induced fatigue,” she says.
Not only does that include having dedicated rest days, but also building recovery periods into your runs and workouts, especially when doing interval training. For example, most HIIT sessions include rest between exercises and sets and even if you’re feeling energetic, Hunter advises taking those seriously because shortening the recovery periods could set you up for overtraining and injury risk.
A research review in the International Journal of Sports Physiology and Performance reports that overtraining syndrome—characterized by an imbalance between training and recovery—is recognized by effects like decreased performance, more fatigue, and mood disturbances.
Fatigue from overtraining can take several forms, according to the National Academy of Sports Medicine. Not only can you tire faster during a run or workout due to overtraining, but you may also have a changed perception in your rate of exertion, as well as a lack of feeling refreshed after you do rest. Overtraining can also cause fatigue and low energy to linger throughout the day, leading to a decline in motivation and enthusiasm for exercise.
The bottom line: You can’t keep pushing it in your workouts in hopes of improving your fatigue resistance. Without proper rest and recovery, you’ll do the opposite. Doing nothing is still doing something for your body.
5. Have a Nutrition Plan in Place
Yes, guzzling a sports drink or slurping back gels or gummies during a run will help you fight off fatigue—your body and mind run primarily on carbs after all—and this is definitely something to practice during training to find the right amount and frequency of intake. But you also need to take a more holistic view of your eating plan to make the most of the work you’re putting into fighting fatigue.
Research indicates that a diet high in carbohydrates overall can benefit endurance performance, particularly if you’re running at a high intensity (like on race day). Figuring out how much you need and timing it right for your runs can be a little tricky as it’s very individualized. But science suggests going for about 1 to 4 grams of carbs per kilogram of bodyweight (about 0.5 to 1.8 grams per pound) about one to four hours before exercise.
To make sure you top off your glycogen stores after a workout (that’s the stored form of glucose), you also need solid recovery meals, especially during training when you may have multiple workouts in a row. Research indicates getting carbohydrates—about 1 gram per kilogram bodyweight per hour or about 0.5 grams per pound bodyweight—in the two to four hours after finishing exercise. Aim for a combo of glucose and fructose for easier digestion (which you’ll find in dried fruits). You’ll also want protein.
Upping your carb intake in the days before long runs or race day will also help top off your glycogen levels so you have the energy to finish strong.
If you have trouble nailing down your nutrition—and you still feel fatigue after trying these strategies on your own—working with a sports dietitian can help.
How to Determine Progress in Fatigue Resistance
In terms of how to determine if you’re improving your fatigue resistance, it’s likely you don’t have access to a research lab that can do occasional muscle biopsies to look at your fast-twitch and slow-twitch fiber percentages, so Hunter suggests an easier, more accessible method: Track how you feel.
“Perceived effort and perceived fatigue shouldn’t be underestimated as training tools,” she says. “The more you tap into how your body is responding, the greater your body awareness becomes. People like to use their heart rate to measure effort, but in many cases, using that awareness can be just as useful.”
You could also use a training log to track how you feel during and after long runs and interval workouts.
If you make it to the end of your hard workouts feeling energized, you know you’ve made some strides toward building fatigue resistance. On the other hand, if you still feel like your workouts are hard to get through day in and day out, it’s time to check in on these fatigue-resistance factors (and maybe enlist some expert help).
