"Whether it be a phone, a water bottle, a set of keys, a towel, or a shirt, running with something in one hand while running can cause you to use your body differently than if you were running with nothing," Men's Health Fitness Director Todd Liubinskas says.
The average smartphone can weigh up to couple of hundred grams and while this doesn't seem like much, even small imbalances in the distribution of weight across your body as you run can have subtle knock on effects.
"When you are running, the aim is to keep consistent cadence. Equal distribution of weight and momentum allows for a smoother run," he explains. "Now, once we place something into our hands, that causes an effect of asymmetry within the running style you are used to."
By making one arm heavier (and swinging it back a forth for 30 minutes) your body will try to compensate for the imbalance by working certain muscles harder than others. This can lead to strain and injury, particularly in your shoulders, hips and knees.
"Pending on how far you are running, leave your phone in the car, and get the selfie at the start and at the end," Todd recommends. "My advice would be do take some mates running with you, and have a chat to each other, rather than be on your phones, the memories will last longer, and the run will be more enjoyable."
Another option? Invest in a waist belt (or, ahem, num bag) to store your phone in around the centre of your body.