Muscle Fatigue vs. Mental Fatigue: How to Determine Which One Is Holding You Back

Running on empty? How to tell if it’s your body or brain (or both) that needs support.


BY KARLA WALSH |

Many of us have been there, felt that: You just woke up from your usual eight hours of sleep, you’ve slipped on your running tank and shorts, you’ve laced up your shoes, and yet, you’re simply not raring to go. Instead, your gas tank seems to hit “E” for a reason you can’t quite pinpoint. That feeling? It’s called fatigue.

Because this sensation has so many potential causes and symptoms, it’s often tough to tease out what kind of fatigue you’re experiencing. But once you do figure it out, you’re able to tackle roadblocks head-on and get back up to speed ASAP.

To get you on the level of fighting fatigue with fury, here’s your guide to what it is, how to differentiate if it’s your mind or your muscles that feel off, and the best ways to tackle extreme tiredness.

The Full Scoop on What Fatigue Really Means
By definition, fatigue is a condition that makes you extremely tired, often to the point where you can’t function. If you can’t wake up without hitting snooze, find typical daily tasks difficult to accomplish, and if your days feel longer and tougher to conquer, it’s likely fatigue that’s ailing you.

This is different from being tired, particularly from lack of sleep. When you’re tired, you’ll often be able to bounce back to full strength and speed after a good night of shut-eye. With fatigue, recovery often involves a multi-pronged approach.

“People may experience various aspects of fatigue including muscular fatigue, mental fatigue, emotional fatigue, fatigue due to inadequate nutrition, or fatigue due to a lack of sleep quality or quantity,” says Dr Suzanna Russell, a postdoctoral research fellow in mental fatigue and recovery at the Sports Performance, Recovery, Injury, and New Technologies (SPRINT) Research Centre at the Australian Catholic University in Australia.

When we put our bodies and brains through the paces, we put more demands on ourselves either physically, mentally, or both, Russell says. So as we’re training for a race or running recreationally, or even when we’re cranking out challenging brain-based tasks, cells can become “overloaded” by the physical and mental stress, says Elisabeth Gainsborough, M.S. in exercise physiology, and a certified personal trainer and clinical fitness specialist at Northwest Community Healthcare Wellness Center in Illinois.

To adapt to the forces of stress and fatigue, our bodies often experience temporary reductions in performance. Fatigue may indicate that our body is in need of more recovery or downtime between training sessions. This can manifest as delayed onset muscle soreness (DOMS), feeling “fuzzy,” lacking motivation, and more.

“In many cases, these new levels of stress may leave you feeling exhausted in all aspects — and it’s hard to know what’s really holding you back,” Gainsborough says. “Most of the time, your mental fatigue will affect you physically, and your physical fatigue can make you think you are more tired than you actually are.”


How to Differentiate Between Mental Fatigue and Muscle Fatigue
If you frequently feel low in energy, Gainsborough recommends asking yourself: Is your body able to recover between runs? Are you getting enough sleep? Are you giving your body enough fuel? Is your training programme too strenuous? “There are a lot of aspects you need to consider in order to help determine what is really slowing you down,” Gainsborough says.

Differentiating between cognitive, muscle, and general body fatigue can be challenging due to overlapping symptoms, adds Dr Haley Perlus, a sport and performance psychologist in Denver. However, some guidelines will help you tell them apart:

What It Means to Experience Mental Fatigue
Cognitive fatigue, or mental fatigue, is a psychobiological state that happens when your brain gets overworked, Russell explains. Prolonged periods of cognitive activity, such as studying, problem-solving, or intense concentration can cause mental fatigue, as can stress, certain medical conditions, or lack of high-quality sleep. “Your ability to refocus your mind on something other than the fact that you are just exhausted may seem close to impossible,” Gainsborough adds.

Mental fatigue symptoms include:

  • Feeling mentally drained
  • Difficulty focusing
  • Impaired memory
  • Reduced problem-solving abilities
  • Feeling apathetic to activity or thoughts
  • Increased errors
  • Slower reaction times
  • Difficulty self-regulating emotions
  • Withdrawal
  • Changes in appetite and/or mood

Research on athletes suggests that mental fatigue is a largely separate phenomenon from physical fatigue, Russell says, although both conditions interact. The most consistent way we see mental fatigue present physically in research: An increased rate of perceived exertion (RPE) during the same physical output. That means your 6 mins/km pace that usually feels like a breeze could render you feeling totally tapped out — or, at least, will feel a lot more challenging than if your brain wasn’t feeling quite so taxed.

A dead giveaway that you need to focus on your mental state, according to science: You lack focus or discipline, or notice substantial decreases in motivation or enthusiasm for tasks you once found enjoyable.

6 Ways to Overcome Mental Fatigue
The best way to manage mental fatigue is to take a proactive approach to minimise the mental fatigue at the source, Russell says. This means taking short hourly breaks during mentally-taxing projects, limiting out-of-office work time, and spacing out brain-intensive tasks when possible.

In addition, the experts we spoke to recommend these strategies:

1. Limit social media use
Social media use prior to exercise has been shown to impair performance, Russell explains, so avoid it an hour before your workout and space out use throughout the day.

2. Find a mind-focused practice
“Mindfulness and meditation techniques can help alleviate mental fatigue by promoting relaxation, reducing stress, and improving mental clarity. This helps to focus attention on the present moment, letting go of distracting thoughts,” Perlus says. Just 13 minutes per day of meditating for eight weeks straight has been shown to boost mood, increase ability to regulate emotions, improve attention, and decrease anxiety levels, according to research.

3. Fuel wisely
“Poor food choices, alcohol, and not enough water can certainly play a role in how fatigued we feel during the day, regardless of our training or exercise program or mental challenges,” Jacque Crockford, a San Diego-based certified personal trainer and senior product manager for the American Council on Exercise tells Runner’s World.

While this is true for mental and physical fatigue, the mental link appears to be related to our gut microbiome and the conversation that occurs all day, every day, between our intestines and our minds (a.k.a. the gut-brain axis). To feed the good gut bacteria and your energy levels, aim for a balanced mix of macronutrients (carbs, protein, fat), as well as enough fibre. Women should stick to one alcoholic drink per day, max, and men should sip on two or fewer.

4. Get a boost by way of caffeine
Research indicates that downing some coffee can help to mitigate the effects of mental fatigue on performance, Russell says. You just want to steer clear of caffeine within six hours of bedtime, at least one study suggests, or it can mess with your sleep.

5. Pepper in some positive self-talk
It might sound woo-woo to have a go-to mantra or a flip on your optimistic switch, but science proves that self-talk is more important than you think, Gainsborough says. If you’re feeling mentally drained during your workout, “find something to focus on and convince yourself that you are enjoying the run and going to succeed,” she adds.

Establishing a more uplifting mental conversation on the run might include identifying negative thoughts and replacing them with motivation phrases, like “you got this” or “you are strong.”

6. Set yourself up for sleep success
Crockford swears by a slow yoga flow, avoiding TV and screens close to bedtime, and listening to a soothing instrumental playlist to wind down. Sleep is very individual, so play around with what environment and pre-bed rituals work for you. Above all, the goal is to “establish a regular sleep routine, aiming for eight hours of quality sleep each night,” Perlus says.

What It Means to Experience Muscle Fatigue
Muscle or general body fatigue involves feelings of tiredness or exhaustion that are correlated with either the depletion of glycogen stores or the build-up of metabolic waste products from intense physical activity, repetitive muscle contractions, or sustained muscle exertion, Perlus says. Inadequate rest or sleep, emotional stress, very hot temperatures, certain medications, and some medical conditions can contribute to this type of fatigue.

Scientists usually define this as a “difficulty to initiate or sustain muscle activities” at your normal levels. Physical fatigue usually has little to no impact on cognitive alertness.

Muscle fatigue symptoms include:

  • Weakness
  • Feeling heavy in legs or feet
  • Decreased muscle performance (power, coordination, and/or endurance)
  • Feelings of stiffness and/or soreness
  • Shortness of breath
  • Decreased energy levels
  • Diminished performance
  • Possible cramping, trembling, or twitching of the muscles
  • Changes in appetite and/or mood

Even after you receive a full night of sleep, your body’s energy may remain low, Gainsborough says — until you integrate some of the fatigue-combating strategies below.

7 Ways to Overcome Muscle Fatigue
Because each person recovers at a different pace and many of us are often fatigued for more than one reason (say, a long run one day and a tough strength workout the next), the best muscle fatigue Rx varies per person, Russell says. To try to prevent or reduce body fatigue in the first place, aim for a consistent exercise schedule with rest days in the mix.

Usually, 24 to 48 hours per week of active rest is ideal to support recovery, Crockford says. On these days, incorporate some form of less-intense movement that uses your joints and muscles in different ways than running, such as yoga, walking, or Pilates.

“Regular physical activity helps reduce body fatigue and boost energy levels. Exercise improves circulation, releases endorphins, and enhances overall fitness and stamina,” Perlus says. The catch is finding the right balance of exercise and rest.

Beyond that, try these pro tips to bounce back from physical fatigue:

1. Keep calm and snack on
If you’re experiencing some mild muscle fatigue during a race (which might feel like you’re running out of gas while your brain and heart are rearing to forge ahead), Gainsborough suggests giving your body a boost with some easy-to-digest carbohydrates or a sports drink.

2. Take five for a body scan
After your workouts or before bed, carve out five minutes to perform a body scan to see where you might be having any physical sensations, like tightness, soreness, or pain. This can help you customize your active recovery or stretching routine to focus on TLC for that area in particular. If it’s intense, you may want to tweak your training schedule accordingly, say, by adjusting your perceived exertion from a 7 out of 10 to a 5 out of 10. If you think you might be injured, consult with your doctor.

3. Treat your muscles
Foam rolling, massage, mobility exercises, stretching, and yoga can help support recovery from intense training and reduce DOMS symptoms, Crockford and Russell agree.

4. Take a bath
Ice baths may reduce acute inflammation, improve perceived recovery, and reduce muscle soreness, Russell says. Stick to 10 to 15 minutes or less, she suggests.

5. Slip on compression gear
For many runners, the main source of aches comes down to the legs. Post-workout, consider wearing a pair of compression socks to promote blood flow, and in turn, support recovery, Russell recommends. “These have largely inconclusive evidence regarding performance benefits, but generally improve perceived fatigue and soreness and enhance how a recovering individual feels,” she explains.

6. Integrate stress-management techniques
Chronic stress can contribute to increased body fatigue. “Explore relaxation techniques, such as deep breathing exercises, progressive muscle relaxation, yoga, or meditation,” Perlus says. “These practices can help reduce muscle tension, lower stress hormone levels, and promote a sense of calm.”

7. Eat and drink to support recovery
Proper nutrition and hydration combat body fatigue. Ensure you consume a balanced diet rich in whole foods, including fruits, vegetables, lean proteins, whole grains, and healthy fats. Avoid excessive caffeine, sugary foods, and processed snacks that can lead to energy crashes.


How to Prevent All Forms of Fatigue
Regardless of where the fatigue originated, it’s important to build rest and recovery into your training plans and between cognitive tasks so that you can recharge and allow your body and mind to recover and perform at their peak.

Prioritising sleep, breaks, relaxation (such as meditation, yoga, or a quiet walk in nature), and positive thinking can help you overcome fatigue. These aren’t one-and-done tasks, though. Just like you need to train early and often to be ready to set a personal best time, you need to sprinkle in these fatigue-fighters throughout the week to bounce back from tough workouts and draining mental tasks.

It can be easy to get lured into focusing on the marginal gains or “one-percenters” that are advertised to improve performance, such as specific gear or electrolyte powders, Russell admits. But she says that focusing on getting the basics right—scoring seven to nine hours of sleep, consuming a well-balanced diet and ample hydration, and preparing with a training program based on scientific principles and individualized for your goals — is what will really move the needle and keep you running strong for the long haul, without fatigue (muscle or mental!) getting in your way.

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