Think disrespecting your recovery only crushes your body? Think again. A 2023 review found that overtraining has serious cognitive consequences—including slower reaction times, worse decision-making, and increased mental fatigue.

Most people focus on the physical costs: disturbed sleep, hormonal imbalances, and declining performance. But overtraining is just as detrimental to your brain. This review analyzed multiple studies on endurance athletes and found that overtrained individuals showed up to 20% slower reaction times—a massive drop that could impact everything from performance to career-ending injury risk.

Like all things training and adaptation-centric, endurance improvement requires that you always do “more.” The problem is endurance training is already loaded with volume, so it doesn’t take long to start seeing cognitive performance decline.

The Cognitive Cost of Overtraining

You already know overtraining can make you feel like a lifeless noodle, but did you know it can also make you slower in the head? Here are the key brain-related symptoms of overtraining:

1. Slower Reaction Time

Studies show that reaction times can decline by as much as 20% when an athlete is overtrained. That’s the difference between dodging a punch and eating one, making a game-saving tackle or watching your opponent breeze past you. When you’re constantly pushing your limits without allowing proper recovery, your nervous system gets fried.

The 2023 study published in Sports Medicine Open found that this reaction time decline was directly correlated with training volume overload. Athletes subjected to weeks of high-intensity training without sufficient rest showed significant delays in their responses to cognitive tests like the Stroop Color Word test. The test, designed to measure cognitive flexibility and processing speed, showed that overtrained athletes took longer to process and react to stimuli, highlighting the negative impact on split-second decision-making.

2. More Decision-Making Errors

Overtrained athletes make worse decisions. The same 2023 study found that athletes in a state of functional or non-functional overreaching demonstrated increased decision-making errors. This is critical in sports requiring split-second reactions—think fighters, goalkeepers, or race car drivers.

The systematic review also found that in high-intensity sports, such as triathlon and long-distance running, decision-making errors compounded as overtraining worsened. Researchers noted that overtrained athletes exhibited higher levels of cognitive inflexibility, making poor in-game decisions more frequently than well-recovered counterparts. This highlights how chronic training stress doesn’t just affect the body but fundamentally alters mental processing.

3. Increased Mental Fatigue and Brain Fog

Ever feel like your brain is lagging, even after a full night of sleep? That’s because your nervous system takes a beating from chronic overtraining. The cognitive drain isn’t just about your sport—it seeps into your life, making studying, working, and even socializing harder.

The study emphasized that mental fatigue due to overtraining is similar to cognitive impairment seen in sleep deprivation. Researchers compared reaction speeds of overtrained athletes to individuals who had been sleep-deprived for 24 hours and found nearly identical impairments in cognitive function. This suggests that prolonged, excessive training can induce the same sluggish mental state as extreme fatigue.

4. High Impulsivity Under Fatigue

When your brain is running on empty, you make impulsive choices. That could mean throwing wild, desperate shots instead of strategic counters, pushing through pain that leads to injury, or even disregarding proper recovery strategies. Studies show overtrained athletes are more likely to act on impulse, often to their detriment.

The Sports Medicine Open review found that athletes who were overreached displayed increased impulsivity and impaired response inhibition, meaning they were more likely to take unnecessary risks. This can be a recipe for disaster in high-stakes sports where patience and calculated decision-making determine success.

The Myth of “More Is Better”

We get it—the hustle culture in sports makes it feel like more training equals more gains. But a stack of research says otherwise. Adding volume just for the sake of it doesn’t necessarily improve performance and can actually make you worse.

Functional overreaching (a short-term increase in training volume) can lead to adaptation when properly managed. But non-functional overreaching (when you don’t recover adequately) and full-blown overtraining syndrome (OTS) lead to a cascade of problems, including long-term performance decrements and increased injury risk.

The study highlighted that the differentiation between functional overreaching and non-functional overreaching is critical. While slight fatigue in controlled training blocks can promote adaptation, excessive fatigue without proper deloading periods leads to burnout, prolonged central nervous system (CNS) dysfunction, and even depression-like symptoms in extreme cases.

The Body’s Warning Signs: Don’t Ignore These Red Flags

Overtraining sneaks up on you like a slow-burning fire. Here’s what to watch for:

• Persistent soreness that doesn’t go away (not just post-leg-day pain, but weeks-long aches)

• Disturbed sleep patterns (waking up tired despite getting 8+ hours)

• Elevated resting heart rate (your body struggling to return to baseline)

• Loss of motivation (that burning drive suddenly feels like a chore)

• Increased injuries (nagging pain turning into chronic issues)

• Constant fatigue (even after days off, you still feel exhausted)