Durdling on your phone between sets may seem like a harmless diversion, but research suggests it may hurt your gains.

For example, in a study conducted by scientists at the Federal University of Paraíba, researchers had 16 experienced weightlifters do 3 sets of squats to failure, then look at social media or watch a documentary for 30 minutes before doing another 3 sets of squats to failure. 

The results showed that the weightlifters who watched the documentary completed about 15% fewer reps in their second bout of squats.

Conversely, the group pottering on social media performed 29% fewer reps. 

The researchers also found that the social media group experienced much higher mental fatigue (~60% vs. ~15%), a psychobiological state characterized by feelings of tiredness that people typically experience after demanding cognitive tasks.

Other studies back this up.

A meta-analysis conducted by scientists at the Autonomous University of Madrid concluded that mental fatigue hinders strength endurance (the number of reps you can perform before failure) by 10-to-20%.

This reduction in reps can undermine your gains, as doing sufficient volume is a critical component of building muscle. 

Several other studies also show that using technology for mentally demanding tasks, like browsing social media, can adversely affect athletic performance, hindering your ability to swim, run, cycle, and play sports like soccer and cricket to the best of your ability.

Interestingly, mental fatigue doesn’t appear to affect maximal strength, a silver lining for those who enjoy watching TikTok before testing their one-rep max.

How can you prevent smartphone-induced mental fatigue from hindering your gains?

Here are three good starting points:

  1. Avoid using your phone for mentally engrossing tasks (e.g., browsing social media, web surfing, and video watching) for at least 30 minutes before or during your workouts. If you find this challenging, download a program that blocks social media (and other websites) for a pre-set period, like Freedom.
  2. If you can’t resist diddling around with your dopamine dispenser (phone) before your workout (or you have to deal with another task that leaves you feeling strained), consider reducing your training intensity. Rather than striving to complete each of your sets 1-to-3 reps short of failure, aim to finish them 4-to-5 reps shy. This isn’t optimal for muscle growth, but it’ll prevent strength loss, ensuring you won’t have to lighten the weights in your next workout (when you’re hopefully more present and fresh).
  3. Trade browsing social media between sets for alternative strategies that enhance performance, like visualizing your next set, reciting weightlifting cues, and listening to music.

If you want to learn more about how to maximize your time in the gym and gain muscle and strength effectively, check out my fitness books for men and women, Bigger Leaner Stronger and Thinner Leaner Stronger.

Takeaway: Performing mentally engrossing tasks, such as browsing social media, answering email, or web surfing immediately before and during your workouts can decrease the number of sets and reps you can do, which reduces your ability to gain muscle and strength.

This article is part of our Research Review series, which explores a scientific study on diet, exercise, supplementation, mindset, or lifestyle that will help you gain muscle and strength, lose fat, perform and feel better, live longer, and get and stay healthier. 

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