According to News24, pumping loud music into your ears for a prolonged period of time can impact your balance through the vestibular system, making running on the treadmill more dangerous. It can also potentially damage your hearing in the long run. Although headphones may make it easier to concentrate, scrolling endlessly through songs while trying to find the right one for the exercise in question could be robbing you of valuable workout time. Likewise, if your music is too loud it may be distracting fellow gym goers, so try not to block everything out exactly. It's worth noting, too, if the cord on your earphones isn't the right length, it might restrict your movement, making it more difficult to strength train properly. You could even hurt your neck while working your core. 

Also, did you know you should be cleaning your headphones regularly after each use? Sweat and bacteria cling to them, which can lead to ear infections, particularly if they're frequently tossed into your bag with the rest of your gear. However, as with headphones themselves, there's no one size fits all rule here. As trainer Sue Reynolds Reed advised, try one exercise session without headphones, to ensure your breathing and focus are both on point (via Health E News). Put simply, if headphones assist with your workout, include them. If they're distracting you, it's best to go without. Either way, keep them clean and take note of any changes in your hearing, just in case.