Can A Pre-Race Poop Make You Faster?

+ Male Athletes Are (Silently) Underfueling—And It’s Killing Their Performance

Last Updated: May 7, 2025 4:09 pm

Brady Holmer

Brady Holmer

Brady Holmer has a Bachelor’s degree in Exercise Science from Northern Kentucky University and a Ph.D. in Applied Physiology and Kinesiology from the University of Florida.

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Can A Pre-Race Poop Make You Faster?

We all get nervous before a big race or a workout. Unfortunately, this can sometimes lead to one (or more) trips to the port-a-potty, perhaps derailing our pre-race routines.

But the physical relief from going “number 2” might also be accompanied by a mental boost. If you’ve ever felt mentally sharper after a well-timed bathroom break, science might finally have your back.

A new study on elite triathletes found that defecation (yes, really) led to improved cognitive performance on the Stroop test, a classic measure of executive function. Even more intriguing is that when athletes took magnesium oxide—an over-the-counter supplement known for its laxative effect—the cognitive boost was even stronger.

Could your gut be playing a bigger role in performance than we previously thought? And if so, what does this mean for runners? Let’s break it down.

Researchers conducted a study on 13 elite triathletes. Each participant performed the Stroop test—a cognitive task that measures reaction time and executive control—under three conditions:

1. No defecation 2. Defecation without magnesium 3. Defecation induced by magnesium oxide supplementation

Pooping enhanced cognitive performance—every athlete performed better on the Stroop test after defecation, regardless of whether it was natural or magnesium-induced. However, magnesium made the effect even stronger. With magnesium, 100% of participants improved their test performance, compared to 69% who improved after non-magnesium defecation.

Oxygenation levels in a region of the torso right below the navel—which were measured using Near-Infrared Spectroscopy (NIRS)—decreased during the Stroop test in both defecated conditions, suggesting increased metabolic activity in this area. Meanwhile, no significant blood flow changes were observed in the prefrontal cortex—a brain area key for cognitive function.

The researchers propose a potential “rectum-brain connection”—a direct link between gut activity and cognitive performance.

So, how can runners use this advice?

• While we already know that an upset stomach can ruin a race, this suggests that even minor gut irregularities might impact cognitive sharpness—which is crucial for pacing, strategy, and decision-making under fatigue.

• Pre-race bathroom habits might be more important than we thought. If defecation enhances cognitive function, going to the bathroom before a race might not just be about comfort—it could actually help optimize reaction time, focus, and execution.

Does this mean you should down magnesium supplements before every race? Not necessarily. Runners should be aware that too much magnesium could also lead to an upset stomach. But it does suggest that a pre-race “gut routine” should be a part of performance strategy, not an afterthought.

🎙️ Podcast: The (Legal) Sub-2 Marathon: When, Where & Who Will Do It?

This year could be a historic one for the marathon. Katelyn, Alex, and Michael break down the science, strategy, and races where a sub-2 marathon could actually take place in 2025. 🌍

Will Nike (or Adidas) make a big Breaking2 style push at a Marathon Major? What will be the next shoe tech revolution? And most importantly—who will be the one to do it? 🏆

Watch or listen below for our bold predictions and insider takes! 🎧🔥

WATCH HERE

Male Athletes Are (Silently) Underfueling—And It’s Killing Their Performance

Eating disorders are unfortunately common among endurance athletes, and the discussion has often focused on female athletes. But what about men?

New research highlights that male athletes are also at risk of Relative Energy Deficiency in Sport (RED-S), a condition that can impair health and performance due to chronic under-fueling. The problem is that most male athletes—and even many coaches—don’t recognize the warning signs.

I’m positive there were several times in my career when my fueling was wholly inadequate to support the training I was doing, and my health and performance suffered as a result. Did I have RED-S? Who knows, as I was never diagnosed. But that’s part of the problem—a lack of awareness of the prevalence of this condition.

Researchers involved in this new study analyzed male athletes aged 15–30 from sports medicine clinics at Boston Children’s Hospital and Stanford Medicine. Athletes filled out a detailed health and training survey and were divided into two groups: a group flagged as having low energy availability based on three surrogate markers of having a history of an eating disorder or disordered eating, and a group without signs of chronic under-fueling.

Male athletes with low energy availability were nearly 3 times more likely to have cardiovascular dysfunction such as heart rate abnormalities or circulatory issues, 3.2 times more likely to have psychological illness such as anxiety or depression, and more likely to report gastrointestinal, immune, and metabolic issues.

Under-fueling also wrecked performance. Athletes with low energy availability reported decreased training responses, poorer endurance performance, and lower levels of muscle strength, coordination, judgment, and irritability.

Surprisingly, there were no significant differences in bone health, hormone levels, concentration, or injury risk—which differs from findings in female athletes. This suggests RED-S manifests differently in men, potentially leading to more subtle but serious health consequences.

What this means for runners, coaches, and parents of athletes:

• Low energy availability is a bigger problem in male athletes than we think: RED-S is often thought of as a female athlete issue, but this study makes it clear that male athletes are at risk, too.

• You don’t have to be underweight to have low energy availability: Athletes of all body types and abilities can suffer from RED-S if they fail to match energy intake to training demands.

• Training harder won’t fix poor fueling: A greater likelihood of a decreased training response means that more training doesn’t equal better performance if you’re not fueling properly. Runners experiencing stagnation, fatigue, or poor recovery should consider nutrition—not just training volume—as a potential culprit.

• Screening for REDs in male athletes needs to improve: Low energy availability is probably underdiagnosed in men because the symptoms are less obvious than in women.

If you or an athlete you know is training hard but struggling with fatigue, poor endurance, irritability, or mental burnout, it might not be overtraining—it might be under-fueling.

What Your Fitness Tracker Can (And Can’t) Tell You About Your Training Response

How many times have you woken up, checked your sleep score, and second-guessed whether or not you should do your scheduled hard interval workout or scale back because your watch says so?

Wearables aren’t just for “biohackers” anymore—they’ve taken over endurance sports. We are constantly told these devices can optimize our training, recovery, and performance. And while data from our devices can be fun to look at, how much can it really tell us? And do these metrics actually predict how well we’ll adapt to training?

A recent study set out to answer that question by tracking 24 recreational runners through a structured overload training block while monitoring their endurance performance, sleep, and recovery with a wrist-worn wearable. The researchers wanted to see whether objective sleep and recovery metrics could predict improvements in a 3000-meter time trial at the end of the 5-week training period.

Researchers divided the study into three phases: A 3-week baseline period of normal training, a 2-week overload period where training volume increased by 80%, and a 1-week recovery period where the participants resumed their normal training.

Runners completed a 3-kilometer time trial at the start and after each phase. Throughout the study, they wore a device on their wrist to track sleep quality, heart rate, heart rate variability (HRV), and breathing rate. Subjective recovery was assessed daily using questionnaires on muscle soreness, sleep quality, and perceived strain.

Here’s what they found:

Training overload clearly impacted subjective recovery (how the runners felt), increasing their perceived muscle soreness and strain. Sleep quantity and quality (as measured by the wearable) remained unchanged—meaning training didn’t noticeably consistently affect sleep patterns. However, one metric did predict training adaptation: a combination of heart rate, heart rate variability, and breathing rate.

The researchers referred to this metric as the “nightly recharge” score. Think of it as how much the nervous system recovers from night to night. This “recharge score” was strongly correlated with training adaptation. Runners with lower (worse) values during the overload period improved their 3-kilometer time less than those with better scores. Essentially, runners whose bodies didn’t fully “bounce back” overnight didn’t see as much performance improvement.

What does this study tell us about which metrics of recovery to focus on and which ones to ignore?

Many runners fixate on how many hours they sleep, but this study suggests that HRV, breathing rate, and even resting heart rate might be better indicators of recovery and adaptation than total sleep time, sleep quality, or sleep stages.

And let’s not forget that how you feel still matters. We often ignore subjective recovery cues because they “don’t feel accurate.” But muscle soreness and perceived strain clearly reflected training load in this study, suggesting that simple self-assessments can be just as important as high-tech tracking.

So, should you check your HRV every morning? Maybe. But don’t ignore the old-school method of listening to your body—it might be just as effective. Ultimately, the ideal approach is to use both. A combination of wearable recovery metrics and subjective recovery ratings could be the best way to adjust training and prevent overtraining. It’s the best of both worlds.

The free full text of this study is available from the journal Sensors.

SHORT STUFF You Don’t Want To Miss

Should you ditch the gloves and wear socks instead?

In a Runner’s World piece by contributing writer Theo Kahler (whom I happen to know from our online interactions), he makes a compelling case that “sittens” (socks worn as gloves) make for a cheaper and more effective cold-weather option for keeping your hands warm. I’ve tried this tactic before and it does work well—mittens trap heat better than gloves that separate your individual fingers. Plus, if you need to wipe some snot (or perhaps something else) during the run, “sittens” are easily discarded (and you won’t regret losing a $30 pair of expensive tech gloves).

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