Muscles are either postural or phasic. Postural muscles are mainly slow-twitch. Tight and short, they maintain our posture and support our endurance. Phasic Muscles are mostly fast-twitch. They support movement and fine motor skills but tire and stretch more easily than postural muscles.
Postural and phasic muscles work together in pairs. Typically, the (agonist) postural muscle tightens while the opposing (antagonist) phasic muscle stretches.
Four Examples of Postural Muscles and Opposing Phasic Muscles
Postural: Pectoral Major (Chest), Psoas(Core Muscle), Bicep, Hamstrings(Back of Thigh)
Phasic: Rhomboids(Back between Shoulder Blades), Abdominal Muscles, Tricep, Quadriceps(Front of Thigh
Have you ever noticed someone working their pectorals on a bench press machine but not exercising their rhomboids? If the pectorals are too strong relative to the rhomboids, one or both shoulders may pull forward and risk injury to the shoulder joint. Do you know people who strengthen their core but don't work their abdominals? This imbalanced exercise risks injury to the lower back because short, tight psoas can flatten the lower back and cause a sacral misalignment. (The sacrum is a triangular bone just below the bottom vertebrae.)
Building too much relative strength in certain muscles by emphasizing or neglecting one element of a pair can lead to muscular skeletal imbalance or joint instability.
Our muscles do not act in isolation. If one is out of balance (misaligned) another will react to keep the body in balance. The body's reaction to misalignment can involve multiple muscles with eventual difficulties such as knee pain, shoulder pain, poor posture, scoliosis, and bunions. Prevention and treatment may be as simple as a yoga practice with a teacher knowledgeable in alignment. Particularly, as we age, a consistent balanced yoga practice becomes vitally important to maintain good health.
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