People who constantly exercise their thumbs by using their smartphones could ultimately be harming their physical health.
A new study by researchers at Kent State University found a link between heavy smartphone use and reduced fitness levels among university students.
Researchers Andrew Lepp and Jacob E. Barkley, associate professors in Kent State's College of Education, Health and Human Services, found college students who reported the highest smartphone use - averaging 14 hours a day - were less fit than those who used the devices less often.
"There's no 'phone potato' term, but maybe there should be," Barkley said. "We're just scratching the surface here. I don't think they think about the consequences of sitting and playing with your phone."
Brent Gray Jr, 19, of Cincinnati, admits he would likely be a "phone junkie" if he didn't train as a member of the University of Akron's track team.
The first thing he does when he wakes up is check his phone for texts and updates from Facebook, Instagram, Twitter, Vine and Snapchat, all popular social media apps. He estimates he spends at least 12 hours each day using his iPhone.
"Without my phone, I don't think I'd know what to do with myself," he said. "Without my phone, I'd be disconnected from the world."
Though he stays physically active through track, Gray said he understands how people's lives could become consumed with their smartphones.
"Two hours could go by and you don't even know it," he said.
Lepp and Barkley decided to conduct the study to see whether using mobile phones - despite their portability - shared the same ties to inactivity as playing traditional video games and watching TV.
"There's been evidence that those types of behaviours that are defined as sedentary are inversely related to fitness," Barkley said. "The phones now, especially the smartphones, offer access to all those behaviours we have defined as sedentary."
The researchers surveyed more than 300 Kent State students about their smartphone use and broke them into three categories: low users who averaged 101 minutes daily, moderate users averaging 283 minutes and high users averaging 840 minutes.
Activities that counted toward the total include making calls, texting, sending or reading emails, playing games, surfing the internet, watching videos and using social media. Listening to music wasn't included.
Students were given a test similar to a stress test to measure cardiospiratory fitness.
"If you were someone who used the phone a lot," Barkley said, "you were less fit."
One explanation: frequent smartphone users were more likely to report missing out on physical activities such as walking, running, swimming, working out or playing basketball, soccer, football, lacrosse or racquetball to use their devices.
"I think that high cellphone use could be indicative of a broader array of sedentary behaviours," Barkley said.
Results were published recently by the International Journal of Behavioural Nutrition and Physical Activity.
Brandon Schillig, 22, of North Canton, Ohio, said he tries to find a balance when it comes to his new iPhone. The University of Akron senior estimates he uses the smartphone several hours a day.
"Everything is at the palm of my hand," he said. "It's ridiculous. It's definitely addicting."