Discomfort During Your Workout: What's Happening in the Brain & Body

When you hit the wall during your CrossFit workout (or any high-intensity workout, like conditioning for a sport), it feels like your entire being is screaming "stop!" You know, that burning, heavy, “I can’t do another rep” sensation. A lot is happening behind the scenes, both physically and mentally. Understanding the science behind this discomfort can give you a massive advantage in training and competition.

In this post, we’ll break down what’s really happening in your body and brain, how your perception of effort influences performance, and practical strategies to safely increase your tolerance to discomfort.

The Burn Isn’t Just Lactic Acid

Many athletes blame “lactic acid” for the burn in their muscles during intense exercise, but that’s an oversimplification. In reality, your muscles are producing lactate and hydrogen ions.

• Lactate itself isn’t harmful; it’s actually a fuel your muscles can use during exercise (Brooks, 2020).

• Hydrogen ions accumulate as a byproduct of intense activity, making the environment inside your muscles more acidic. This reduces the efficiency of muscle contraction, contributing to the burning sensation.

• Your nervous system simultaneously sends afferent feedback to your brain.

In other words, the "burn" is not an indication that your body is injured; it's merely a signal to your brain that the muscles are experiencing stress.

Your Brain Regulates Effort

The urge to stop often comes before your muscles truly fail.

• Your brain constantly monitors signals from your body: muscles, joints, and cardiovascular system, and predicts the risk of overexertion.

• That voice in your head saying “slow down” or “stop” isn’t your limit; it’s a protective mechanism designed to keep you safe.

• Seasoned athletes develop the ability to differentiate between danger signals and discomfort signals, enabling them to safely approach their physiological boundaries.

Perception Drives Performance

Performance is greatly affected by how difficult the effort feels. This idea is known as "Rate of Perceived Exertion" (RPE).

Here’s what this means in practice:

• Two athletes of equal skill level performing the same workout may stop at different times, not due to one being stronger, but because one perceives the effort as more demanding.

• Your brain's perception of effort can limit performance before your body actually reaches physical exhaustion.

• Understanding this provides a tool: you can train your brain to handle higher RPEs, safely increasing your performance potential.

Discomfort Tolerance Can Be Trained

The good news is that your tolerance to discomfort is trainable. According to the psychobiological model of endurance performance (Marcora, 2008), exposure and mindset play a huge role in how much effort your brain will allow.

Here’s how to apply this in your training:

Gradual Exposure

The more often you safely push into discomfort, the more your brain learns: “We’ve been here before. We’re okay.” Start small: hold a challenging rep cadence, row at a slightly higher output, hold on to the pullup bar for another rep or two.

Incremental Challenge

Stay just a little longer in the discomfort zone during each session. These small extensions accumulate over time and retrain your brain’s perception of threat.

Focus and Control

Use simple tools to guide your attention:

• Breathing: slow, steady breaths signal safety to your nervous system.

• Self-talk: phrases like “This is discomfort, not danger” reframe your experience.

• Task focus: focus on one rep at a time, not the full set.

Over time, your brain interprets the same level of effort as less threatening, allowing you to push closer to your actual physical capacity. This is how you develop "psychological tolerance."

References

• Brooks, G.A. (2020). Lactate as a fuel: The story of the cell-to-cell shuttle. Exercise and Sport Sciences Reviews, 48(3), 119–127.

• Noakes, T. (2012). Fatigue is a Brain-Derived Emotion that Regulates Exercise Behavior to Ensure the Protection of Whole Body Homeostasis. Frontiers in Physiology, 3:82.

• Borg, G. (1982). Psychophysical Bases of Perceived Exertion. Medicine & Science in Sports & Exercise, 14(5), 377–381.

• Marcora, S. (2008). The Psychobiological Model of Endurance Performance. Sports Medicine, 38(1), 17–36.

• Amann, M. (2011). Central and Peripheral Fatigue: Interactions During Exercise. Journal of Physiology, 589(Pt 1), 67–79.