There are fewer mirrors in the gyms I go to than there used to be. Initially the trend bothered me because they are useful for checking form and it’s encouraging to see the changes in your body, the result of hard training.
The Mirror Hypothesis a T-Nation article by Tim Henriques explores this topic in more detail covering some of the possible causes for performance decreases caused by mirror use with lifting.
One of the comments to the article really resonated with me:
In Supertraining Mel Siff also talks about the proprioceptive benefits of lifting blindfolded. The brain is highly adaptive and will take advantage of every source of sensory imput it can when learning new motor skills. However, since it is also built for efficiency, often one sensory pathway becomes dominant and a reliance on that one system (the visual system in the case of those who habitually lift in front of the mirror) is formed.
That makes a lot of sense. It takes a lot of practice for us to learn how to find a particular position (setting the shoulder blades, aligning the spine, etc…) by going on feeling alone. Mirrors can be helpful but we can become dependent upon them, which is bad because improving function depends on being able to find a position without visual feedback. Training without mirrors is critical for developing body awareness once you have mastered form using external feedback mechanisms.