When fitness instructors refer to your core muscles, they mean more than just your abdominal muscle groups. Core muscles act as a support system for your upper body, spine and pelvic girdle. Weak core muscles force other parts of your body into support roles they were never meant to have. Tightness in your shoulders may be one symptom of a core that needs strengthening.

Core Muscles

Although your abdominal muscles make up much of your core, they aren't the whole core. The long erector spinae muscles that run parallel to your spine, the gluteus muscles of your buttocks and the deep hip muscles such as the piriformis also contribute to core strength. "The New York Times" notes that strengthening only one portion of your core such as the abdominal muscles can cause misalignment elsewhere. It's important to increase core strength overall, not just in portions, so develop a fitness routine that works the muscles of your lower back and hips, as well, to take the stress off your shoulders.

Protect Posture

You use your arms in a forward position for many daily activities. Driving, typing, gardening and a host of other actions leave your shoulders and upper back with a tendency to curve forward. Weak core muscles cannot counteract that tendency to slouch, causing tension in your shoulders as they support your upper body. With a strong core, you hold yourself upright with support from your abdominal and hip muscles instead of placing the strain on your upper back. Your shoulders fall into natural alignment when they no longer need to support the weight of your arms as you sit or stand.

Desk Stretches

Alleviate muscle tightness with gentle stretching in opposition to the usual position of your body. After a long session in front of the computer or at your work desk, take a five-minute break to tilt your head back slightly and draw your arms back as if you were squeezing a lemon between your shoulder blades. This motion runs counter to the hunched posture you might assume at your desk, bringing your body into proper alignment. "Yoga Journal" suggests regular stretches you can do at your desk to ensure good back health.

Core Exercises

While abdominal exercises are not synonymous with core exercises, they play a key role in strengthening your core. Crunches work your abs without producing stress in your lower back, while lunges and squats strengthen the lower core muscles in your hips and buttocks. Pilates and yoga focus on core exercises, so incorporating some poses from these disciplines helps build core strength. Cobra and Upward-Facing Dog poses from hatha yoga elongate abdominal muscles while contracting the erector spinae muscle groups of your back. Ask your doctor before making any changes to your fitness routine. Your doctor may have specific recommendations for increasing your core strength.