A muscle cramp during pregnancy may occur in any muscle or muscle group, but is most commonly experienced in the legs. Muscle spasms that occur in the back or abdomen are also possible. A muscle cramp or spasm is characterized by the following: 1  Involuntary contraction or tightening of a muscle. 2  Usually sudden.
During breathing, these muscles normally tighten and pull the rib cage up. Your chest expands and the lungs fill with air. Intercostal retractions are due to reduced air pressure inside your chest. This can happen if the upper airway (trachea) or small airways of the lungs (bronchioles) become partially blocked.
These muscles play a vital role in the movement of the chest during breathing. They also help to solidify the thoracic region and protect the lungs. Anatomy The 22 pairs of intercostal muscles are broken down into two groups: 11 pairs of internal intercostals and 11 pairs of external intercostals....