I have nothing against people who look in the mirror while lifting. Alright, I do have a problem with people who stand way too close to me and decide to flex while making Buffalo Bill kissy-faces in the mirror. But other than that, I don’t hold it against anyone who wants to look at themselves. However, to achieve maximum performance in compound movements, my personal opinion is that mirrors are detrimental.
I have my clients turn away from the mirror when lifting to keep them focused on the exercise. Invariably, anytime they do face a mirror, their form and execution suffers. It makes sense, when one considers that sight and interpretation of what is seen takes a very large amount of brain processing power. This reduces the efficiency with which a lift can be performed by siphoning off precious mental resources. Their faces quickly show expressions of frustration as they notice tiny errors and try to correct them while trying to accomplish the lift.
These visual corrections are ineffective for the most part since the lifter is in a “tape delay” situation where first they make an error, then see the reflection of the error, then consider how to correct the error, then command the neurons to fire in a way that corrects the error and then visually verify that the error has been corrected. While it is not a very long delay, it is enough to put a person just enough out of sync to be a problem. Being out of sync on compound lifts is a recipe for an injury that is completely avoidable.
There is also the issue of not being able to quickly interpret fore-aft deviations in the mirror. You may want to look in the mirror in order to “watch your form”. Unfortunately, you are seeing a 2D reflection of your 3D body, forcing your mind to interpret that 3rd dimension. Errors that involve moving towards or away from the mirror often are not noticed. You may actually move into the wrong position in order to see yourself better (lifting your head on deadifts, or turning sideways to see your profile during upright rows…yes, I’ve seen that happen).
For simple lifts like bicep curls, using mirrors for form won’t affect your performance. For complex or dynamic movements (cleans, barbell rows, and especially any plyometrics), it’s best to not look at yourself to correct form. Have someone experienced in the lift observe your motion. If you can’t find anyone who knows what to look for, tell them what to look for. With time and practice, you will know from feel if you are in the right position prior to and during every rep.
So there you go. See if you can break the spell of self-staring when doing the complex and heavy stuff. I promise you’ll have much better focus when you aren’t torn between being Tom Platz and Buffalo Bill.