the trapesious muscle
scalene muscles
to make it tight
The muscles that support the spine include the erector spinae, transverse abdominis, obliques, and quadratus lumborum. These muscles help maintain posture and stability in the spine.
Your hamstring muscles.
You can flex skeletal muscles voluntary. These are the muscles you can control and move consciously. Smooth muscles and cardiac muscles, which work involuntarily, cannot be consciously flexed.
Hamstring
The sternocleidomastoid muscles are the ones that flex when the intercostals are flexed. This will also cause the scalene muscles to flex.
To flex your chest, you tighten the muscles that are in that area. This might include your arms or back as well, but you tighten the muscles in your chest and abs.
The primary muscles involved in supporting and stabilizing the thoracic spine musculature are the erector spinae muscles, the multifidus muscles, and the transversospinalis muscles. These muscles work together to help maintain proper posture and stability in the thoracic spine.
Abdominal muscles are trunk muscles that help to rotate and flex the spine. The abdominal muscles are composed of:Rectus abdominus: originates at the pelvis and inserts into the sternum as well as ribs 5-7. This muscle flexes the spine or assists in posteriorly (behind or in back of) tilting the pelvis.External obliques: one of the abdominal muscles responsible for rotation and flexion (position that is flexed relative to neutral or extension) of the spine. Developing external oblique strength is important for spinal stabilization against movement faults.Internal obliques: one of the abdominal muscles responsible for rotation and flexion of the spine. Developing internal oblique strength is important for spinal stabilization against movement faults.Transversus abdominus: an important spinal-stabilizing muscle
Muscles can contract and shorten
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