“Obviously… a ton of nuance here. But many workouts or runs suck because our brain is telling us to stop, although our legs and heart feel fine. Fatigue is a fascinating topic… and central fatigue can be challenging to overcome. We’ve all had those workouts that sucked because our brain wouldn’t shut up. Telling the difference between those and the times when our body tells us to rest is a worthwhile skill to develop. Things like watching your HR… are you 10-15 bpm higher than you should be? Do you feel tired or beaten down? Those days you should walk, hike, walk the dogs, or do some yoga. It’s one thing to train your brain for adversity… it’s another thing entirely to run yourself into the ground.”
Howard Luks, MD, on X 9/30/2024
This passage touches on a central theme for endurance athletes: knowing the difference between central fatigue and genuine physiological fatigue is critical to determining when to persevere and when to rest. To truly understand this distinction, we must delve into central fatigue, its relationship to the body’s other physiological markers, and how monitoring feedback like heart rate (HR) and perceived exertion can help guide us through challenging workouts.
What is Central Fatigue?
Central fatigue decreases the central nervous system’s (CNS) ability to send effective signals to the muscles during exercise. Unlike peripheral fatigue, which is caused by muscle exhaustion, central fatigue originates in the brain. It acts as a protective mechanism, preventing the body from overexertion. Your brain tells your body to slow down, even when your muscles or cardiovascular system still have plenty of energy.
The fascinating aspect of central fatigue is that it's physical and psychological factors as well. The environment, mood, stress, and mental stamina contribute to whether central fatigue manifests during a workout. For athletes, learning to push through central fatigue can build mental toughness, but it’s essential to know the signs of when to pull back.
Can You Continue Running Despite Central Fatigue?
The simple answer is yes but with important caveats. When you experience central fatigue, it doesn’t necessarily mean your body is nearing its limit. The key to managing this fatigue lies in monitoring other physiological feedback—like your heart rate and how your muscles feel. If those markers suggest your body is functioning well, you can continue.
However, elevated heart rate can be a more significant indicator of systemic fatigue, meaning your body may be tired, not just your brain. This is why we should evaluate multiple feedback systems before continuing or choosing to rest.
Knowing when to continue working out or running and when to stop can be challenging. It's a mini-superpower. You never want today's workout to ruin tomorrow's, yet there are plenty of times when it's okay to keep pushing. For paid subscribers, we'll discuss several steps you should take to help determine whether or not your workout is over... or if it's reasonably safe to continue.
Monitoring Physiological Feedback
Using objective metrics like heart rate, rate of perceived exertion (RPE), and muscle fatigue can help you differentiate between central fatigue and overall physical exhaustion:
Heart Rate (HR):
Heart rate zones are key to understanding the body’s effort levels. If your HR is in a zone higher than expected for the type of effort you’re putting in (e.g., being in Zone 4 when you expect to be in Zone 3), this suggests physiological fatigue. In this case, continuing to push could lead to overtraining or injury. When you see a 10-15 bpm elevation above normal for a given workout, that’s often a sign that your body has not recovered adequately or is under stress, and you should consider scaling back.
Perceived Exertion (RPE):
The Rate of Perceived Exertion (RPE) is a subjective measure of how hard you feel you’re working on a scale from 1 to 10. If your RPE is high but your heart rate and other metrics seem normal, it may be central fatigue or mental resistance. Learning to recognize when you’re simply struggling mentally versus when your body is physically taxed is key to becoming a more resilient athlete.
Muscle Fatigue:
Pay attention to how your muscles feel during exercise. True muscle fatigue is different from mental fatigue—if you can still maintain good form and feel strong, you’re likely dealing with central fatigue. However, if your muscles are shaky, uncoordinated, or sore to the touch, these are signs of peripheral fatigue, and you may need to rest.
When You Should Stop
Sometimes, your body sends signals that you shouldn’t ignore. If your HR is significantly elevated or if you feel physically beaten down, it’s crucial to rest. Ignoring these signs could lead to overtraining, burnout, or injury:
Elevated HR in a Higher Zone:
If your heart rate is 15-20 bpm above your usual rate for the same effort, it clearly shows that your body is struggling. This could be due to dehydration, lack of recovery, or general fatigue. When this happens, it’s better to slow down or opt for a lighter workout to prevent further strain on the cardiovascular system.
Feeling Beaten Down:
Chronic tiredness, irritability, and lack of motivation are signs of overtraining syndrome. When you feel consistently beaten down despite taking rest days, it’s a sign that your body is not recovering properly and needs more time to rebuild. These days, switch to recovery activities like yoga, walking, or, you know, reading.
Other Symptoms:
If you experience other signs of fatigue, such as poor sleep, increased soreness, or mental fog, these are additional indicators that your body needs more rest.
Why You Can Sometimes Push Through
On the flip side, there are plenty of times when pushing through central fatigue is not only safe but beneficial:
Building Resilience:
One of the most valuable benefits of pushing through central fatigue is developing mental resilience. This can make future challenges seem less daunting, as you learn to manage the discomfort of fatigue and build confidence in your ability to persevere.
Mental Toughness:
Training through central fatigue can expand your mental limits, teaching you to stay calm and focused when your brain tells you to stop. This can be critical during races or long runs, when mental stamina is as important as physical endurance.
Endorphin Release:
Often, once you push past central fatigue, your body begins releasing endorphins, which improve mood and lessen the perception of pain. This “runner’s high” can make the workout more enjoyable once you break through that initial discomfort barrier.
Managing Central Fatigue
Here are some strategies to help manage central fatigue and push through when appropriate:
Break the Workout into Chunks:
When your brain is signaling fatigue, break the workout into smaller goals. Focus on just reaching the next mile or completing the next set, rather than the entire workout.
Practice Mindfulness:
Mindfulness techniques, such as focusing on your breathing or using positive self-talk, can help you stay in the moment and manage the mental discomfort of fatigue.
Watch Your RPE and HR:
Always monitor both subjective (RPE) and objective (HR) measures during workouts. If your HR stays within the expected range, you’re likely fine to push through. However, if both RPE and HR are elevated, it’s time to consider slowing down or resting.
Conclusion
Knowing when to push through central fatigue and when to rest is essential for athletes of all levels. While pushing through mental fatigue can help build mental resilience and toughness, monitoring heart rate and RPE can provide valuable feedback on whether your body is physically ready to continue.
Elevated HR and signs of fatigue should prompt you to slow down or take a rest day. On the other hand, if your HR is in check and your muscles feel strong, pushing through central fatigue can improve both physical performance and mental endurance. Striking the right balance between these signals will help you stay healthy and perform at your best in the long run. If there are times when you're unsure what to do... an extra rest or recovery day never hurt anyone.
