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One of the biggest gym mistakes is only training your “mirror muscles" — you know, the ones you can stare in the mirror (abs, anyone?). But, there are plenty of muscles that are essential to your overall health as well as your physique. Just because you can’t see it, that doesn’t mean you shouldn’t train it.
Why? Because each major muscle also has a counterpart (for example, your bicep has the tricep, and your quad has the hamstring), as well as numerous smaller, stabilizing muscles. All of these help improve your overall strength, explains fitness expert Shannyn Alexander, instructor at FLEX Studios in NYC and creator of the routine you're about to read. When you just focus on just the primary muscles, they may become stronger than the rest, causing an imbalance, which can lead to poor posture and chronic pain. Here's how to feel better and look better by training the six muscles you may not know about, but should.