The trapezius muscle connects your spine to your shoulder blades," says Chicago physical therapist David Reavy. "It stabilizes the upper body for everything from good posture to a powerful bench press."
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The ability to do any downward pulling movement, like a tennis serve or a pull-up, comes from the latissimus dorsi, or lats. This muscle also links the shoulder blades, upper arms, spine, and pelvis, which makes it a critical stabilizer for the core — and the entire body.
The strength to sprint or squat comes via the gluteus maximus, one of the body's largest muscles, and the ability to balance on one leg from the gluteus medius. Both connect to the pelvis, which means that as with the adductors, if you're sitting all day in the same position, these muscles stop firing properly.
What we think of as the core muscles — the rectus abdominis, or six-pack, and the obliques, which span the entire side of your torso — are essential for bending and twisting. Even more crucial for a solid center is the transversus abdominis. Buried under the other abdominals, this thick muscle wraps around your torso and acts like a girdle, keeping your core tight and aligned.
Hip adductors attach to the inside of your pelvis, and they're what keep you stable and aligned when you walk or run (which also makes them saviors for your knees). Sit all day and these thin muscles can shorten and tighten, pull your pelvis forward, and make your hamstrings seize up.
Located in your lower back, the quadratus lumborum is a muscle most of us don't even know we have — until we neglect it so long that it goes into spasm and causes that familiar back pain and tightness.
Running along the spine from your glutes to your head, the spinal erectors allow you to stand up straight and rotate, and they work with the glutes to power upward-pulling motions like a dead lift or a kettlebell swing.
