We spoke with experts to find out the difference between these two forms of lethargy and the best ways to treat both for better runs.
Runner’s World Staff; Aishia McAdams
The terms “fatigue” and “tiredness” are often used interchangeably, but there are several key differences between them. And those distinctions could influence both how you train, and how quickly you bounce back from your workouts.
Similarities and Differences Between Tiredness and Fatigue Symptoms
Exercise-induced fatigue is an involuntary decrease in the muscles’ ability to produce force or produce a powerful contraction, according to Lindsey Wyatt, D.P.T., doctor of physical therapy at Providence Saint John’s Health Center in California.
She tells Runner’s World that tiredness is more lifestyle-based, and can be affected by factors like sleep disruption, poor nutrition, dehydration, stress, and overall fitness level.
Even mental fatigue can play a role in your running. For example, a study in the International Journal of Sports Physiology and Performance suggests that too many cognitively demanding tasks can have a significant effect on how well you exercise.
Both tiredness and exercise-induced fatigue are distinct from the type of fatigue seen with specific medical conditions such as multiple sclerosis, depression, cancer, lupus, or congestive heart failure, explains Sandra Hunter, Ph.D., director of the Athletic and Human Performance Research Center at Marquette University. In those cases, fatigue is considered chronic and can be debilitating to the point where an individual has difficulty with everyday tasks.
In addition to general lack of energy, a major similarity here is that any of these forms of tiredness and fatigue can reduce your performance, but the degree that it affects your workouts comes down to timing, Hunter tells Runner’s World. Exercise-induced fatigue is often the shortest duration, and depending on your level of fatigue resistance, you might see a reset with just a few minutes of recovery.
Tiredness is usually temporary as well, but may drag on for longer, like an entire day or more. That’s especially the case if you haven’t addressed the source of tiredness—for example, if you’re consistently getting fewer than five hours of sleep per night, research suggests your tiredness is likely to continue until you prioritise more rest. In terms of running-related tiredness, Hunter says this might come up as feeling a little wiped out for a day or two after a race, for example.
Condition-related fatigue involves ongoing exhaustion and lethargy, according to Mount Sinai, and can be worsened by physical activity or mental stress. Also, unlike fatigue from overtraining, you’re likely to have additional symptoms specific to your health concern, such as nausea, joint pain, and shortness of breath.
Both tiredness and fatigue can have similar effects when it comes to motivation, running efficiency, progressing toward goals, and injury risk, says Hunter. The short: these forms of feeling blah don’t help you clock kilometres with vigour.
Tips on Reducing Tiredness
You can address tiredness by working to improve your quality of sleep, as well as getting enough sleep, having a healthy diet, staying hydrated, and managing life stresses, says Wyatt.
“Proper nutrition before, during, and after runs is also an important factor when addressing tiredness,” she adds. “Carbohydrates are the primary source of fuel for our bodies, and should be prioritised for prerun meals.”
During long runs, it is important to maintain fueling with fast-acting carbohydrates in order to continue providing fuel to the working muscles, and this can have an effect both on tiredness and fatigue, according to Wyatt.
“Postrun meals should include a combination of carbs and protein,” she adds. “Carbs will help to replenish energy, and proteins assist in repair of muscles.”
Addressing other potential lifestyle factors is also crucial—particularly stress. When there’s prolonged activation of the stress response, to the point that it becomes chronic—usually defined as several weeks at least, according to the National Library of Medicine—it’s possible to develop a condition called stress-related exhaustion disorder, sometimes called exhaustion syndrome. This can lead to numerous health effects, including high blood pressure, anxiety, depression, skin problems, sleep disruption, and digestive issues.
Even before that point, stress can be enough to cause bouts of tiredness that make it difficult to exercise, Hunter says.
Another potential factor in tiredness is overtraining. According to study in Frontiers in Physiology, poor sleep and overtraining can be bidirectional: If you have several nights of disrupted sleep, that could negatively affect your training. Or if you’re consistently overtraining, you can start to develop sleep issues. Regardless of the starting point, the researchers are clear that both will worsen if nothing changes. The best method to start addressing overtraining is often taking more time for exercise recovery, suggests Hunter, and seeing if that improves sleep quality.
Playing around with different variables like sleep, nutrition, stress, and training frequency and duration can often have a notable effect on tiredness, says Wyatt. If tiredness is a challenge for you, she suggests keeping a training log to track your energy levels each day, along with strategies you’re trying to combat the lack of energy you’re feeling. With that info, you can begin to see patterns in terms of what works best for you.
The bottom line on addressing tiredness: Pay attention to lifestyle habits, including diet, stress management, and (of course!) sleep.
Strategies for Fighting Fatigue
If it seems like exercise-induced fatigue is the culprit—say if you have to stop long runs early or you’re struggling to finish the final rounds of your interval workouts—there are several strategies for increasing your fatigue resistance.
For runners, Hunter says that involves doing both low-intensity endurance sessions, such as easy runs done at about 60 to 70 percent of your max heart rate, as well as high-intensity training like gym-based HIIT workouts or sprint intervals.
“You need both types of training to increase your fatigue resistance, because then you’ll be improving both fast-twitch and slow-twitch muscle fibres,” Hunter adds. Strength training and incorporating rest days into your mix are also meaningful ways to build muscular power and endurance, which reduces fatigue.
How can you tell if it’s working? Try paying attention to how much is in your tank later in a race or a long run, Hunter suggests. If you have tiredness in general, you can usually still accelerate thanks to a burst of adrenaline—like seeing the finish line in the distance, for example—but if you have exercise-induced fatigue, you don’t tend to have that ability to pick up the pace because your muscles won’t have any reserve left.
Another indication of whether you’re experiencing tiredness or fatigue symptoms is how you feel when you’re not running, particularly during a rest day, she adds. If you have daytime sleepiness, lack of motivation to do everyday tasks, and generally feel dulled then it’s likely you’re not recovering effectively and could go into your next training session at an energy deficit rather than fully refreshed.
That info can inform what type of training you might focus on more often, but Hunter adds that addressing both tiredness and fatigue at the same time can be helpful. For example, adding more tempo runs to your schedule to build fatigue resistance, but also making sleep a priority.
An important last note: If you tend to feel fatigue often, even when you haven’t been exercising, be sure to check with your medical provider, as fatigue can indicate that something more serious is going on with your health.
