There's working out, and then there's #WorkingOut.
Good form...and filter.
It's a paradox of the times. If there's an activity that's inherently kind of boring and requires very little of your attention, you're going to do it while staring at your phone. But since staring at your phone is way more engaging than that admittedly boring activity, why bother with the activity at all? Take hitting the gym, for example. One selfie fulfills the need to prove to your followers that you had a killer #workout. Then you can spend the next 55 minutes of gym time giving your undivided attention to your @mentions.
This is the path that has led to the current state of our nation's gyms, as demonstrated by this very cogent video by Razmig.