Smartphone makes you slower.

The science behind why pretending, posting, and comparing make you slower.

Back in 2018—what feels like a lifetime ago shared one of the first experiments on the topic, from 2009, conducted by Samuele Marcora and Walter Staiano—names you might recognize from the psychobiological model of effort, and whom I cite in my book The Nature of Training.

Their experiment involved subjecting a group of athletes to two cycling tests to exhaustion. In the first test, the participants sat and watched a documentary for 90 minutes beforehand. In the second, they spent those 90 minutes doing a mentally demanding task.

What they found was that after performing the mental task, participants reported higher perceived exertion at the same power output and reached exhaustion at an average of 15% fewer watts than those who had watched the documentary.

That same year, 2018, a new study was published by a group of Brazilian researchers led by Flavio Pires. In this study, after completing 30 minutes of mentally demanding tasks requiring high concentration, cyclists were subjected to a 20-minute test. On the days they had completed the mental tasks prior to the test, their performance decreased by 2.7%.

Translated to real life: after a tough day of work—whether physical or mental (studying, concentrating, dealing with stress)—your performance will be lower. Even though more studies are still needed to statistically confirm that mental fatigue affects physical performance, in my personal and professional experience, I have no doubt that the association exists.

After a long day of work, clients, phone calls, or study, your performance will suffer—and this happens via different pathways.

On one hand, we could say that continuing to train while mentally or physically fatigued requires mental effort to push through. The body doesn’t work in isolated compartments, and just as you have to force yourself to stay focused through a long workday, you also have to push yourself to keep going when your perception of effort is screaming at you to stop.

On the other hand, the brain and nervous system are still made of physical matter. Physical fatigue causes physiological changes that signal fatigue to the mind. Likewise, nervous system fatigue—responsible for activating muscles and allowing movement—will impair your capacity to generate force. Similarly, energy depletion reduces mental activation, partly due to increased adenosine levels, among other changes.

We could dive deeper into the physiological mechanisms, but it’s not really necessary. Anyone who has worked hard and then tried to train hard—or vice versa—can feel the difference. Only those who don’t push hard in either domain might think there’s no connection. As a coach, I see it all the time—in myself and in my athletes. It’s frankly ridiculous that some training models still treat mental fatigue as either nonexistent or unrelated to physical fatigue.

Lastly, in those same articles I discussed a bizarre and unpleasant study from Wagstaff in 2014. In this study, cyclists had to watch a video of a girl eating her own vomit before doing a 10-km time trial.

While watching the video, they were split into two groups:

a) Control group: no instructions during video viewing.
b) Cyclists forced to keep a "poker face"—showing no emotion, which is a mentally exhausting form of emotional regulation.

The cyclists who suppressed their emotions rode an average of 25 seconds slower in the time trial. The findings suggest that the mental resources used for emotional self-control increase perceived exertion and impair performance.

This suggests that trying to hide discomfort and put on a poker face may actually reduce performance. It also implies that trying to mask your emotions during pre-race interviews or conversations can mentally exhaust you. So, don’t waste energy trying to fake something you’re not before a competition.

As I concluded at the time: this was the first scientific article suggesting that "posing" on social media is inversely related to performance.

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All of this lays the groundwork for a 2020 study titled Does smartphone social media use affect endurance, power, and performance in high-level swimmers? by Leonardo Fortes and colleagues.

In the study, 24 elite female swimmers were divided into two groups. Both followed the same training program, but the difference lay in the 30 minutes before each training session.

During those 30 minutes, the control group watched neutral documentaries about the Olympics. The experimental group, however, was instructed to use only Facebook, Instagram, and WhatsApp—no games or movies allowed. They weren’t allowed to talk to each other, and participants were isolated in separate rooms.

After eight weeks, the researchers gathered training load data and tested the swimmers over several distances.

The main finding: only the control group improved their times in the 100 and 400 meters. The group using social media worsened in those events.

Additionally, the social media group also showed worse results in aerobic endurance and concentration (measured with the Stroop Task—the one where you see the word “green” in blue text and must say the color, not the word).

These swimmers also reported higher perceived exertion during training. This is key—perceived exertion is a central marker of how much performance you have left in reserve. If effort feels harder at the same intensity, your peak output will be lower.

In conclusion: social media use is exhausting. There are multiple reasons for this.

First, there’s the anxiety of constantly exposing ourselves to others’ opinions and comments. Athletes’ social exposure inevitably comes with criticism—usually toxic and unconstructive—for which no one prepares you. Just like we see only the best in others, we judge others based on idealized standards. That’s how people can even wish harm on Evenepoel for once not signing an autograph for a kid. It takes time to handle this because we tend to think criticism means we did something wrong, when in reality, it’s unavoidable.

If you think about who you criticize—or those close to you—you’ll notice it’s rarely criminals or politicians, but people close to you: someone in your cycling group, at work, in your neighborhood, in your sport. It’s normal—criticism is an evolutionary mechanism to gain status by lowering the target’s. But how is a 24-year-old supposed to manage that after reading vile things about himself in online forums?

Second, seeing only the highlight reels of others' lives can make us feel like our own lives are terrible in comparison (spoiler: no one is as perfect as they look online).

Think about the training-related content you consume. Most of the people you follow aren’t just pros—they're the most successful of the successful. Total outliers. Athletes with superhuman genetics, incredible wins, and multimillion-dollar contracts. These are people you'd never normally know—but now they’re in your pocket 24/7. Paradoxically, seeing that Messi or Pogacar are just regular people doesn’t relax you—it makes you think you can get there too. And spoiler: you can't.

Third, social media constantly exposes us to negative news that triggers fear and activates our fight-or-flight response—keeping us in chronic stress. Evolutionarily, we’re wired to pay more attention to threats than to positives. Mistaking a stick for a snake is safer than mistaking a snake for a stick. As the saying goes, “only the paranoid survive.”

Social media prioritizes content that triggers rage and anger, since it's most addictive. Many people exploit this by deliberately being controversial to gain visibility.

Honestly, reading this study—along with books like Stolen Focus (Johann Hari)—makes me much more cautious about my own social media use. It’s not just that it affects training; it affects your mood, focus, and creativity.

One good strategy: be very careful about who you let into your phone—because whether you like it or not, you’re letting them into the most important part of your life: your mind. We can get the best out of social media without the harm—if we use it strictly for work or learning.

For instance, follow only accounts that teach, inspire, or make you feel good. That way, you can turn a toxic habit into something productive—turn wasted time into time well spent. Also, don’t be afraid to use the mute and block buttons. They’re powerful tools to keep toxic people out of your head.

If you would not eat junk food, don´t let your brain eat junk ideas.

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I don’t know about you, but to me, the fact that something seemingly unrelated to training—like browsing social media—can inhibit training adaptations tells me that the old paradigm of counting kilometers, watts, TSS, and time in zone is outdated.

We need a new model of training—one that helps us understand why the body adapts, how anticipatory mechanisms work, and how to leverage them. One that accounts for how psychological and environmental stimuli—like social media—can either reverse or enhance training gains.

It’s time to break free from limiting theories and approach performance with a new paradigm that integrates sports science, biology, and complex systems thinking.

We will have something better soon :)