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.
Rating Newest Oldest. Best Answer: &nbsp The intercostal muscles are mainly involved in the mechanical aspect of breathing. There are three principal layers; the external intercostal muscles, which aid in quiet and forced inhalation.They originate on ribs 1-11 and have their insertion on ribs 2-12.The external intercostals are responsible for the elevation of the ribs, and expanding the transverse dimensions of the thoracic cavity.oth the external intercostal muscles and the intercondral elevate the ribs, thus increasing the width of the thoracic cavity, while the diaphragm contracts to increase the vertical dimensions of the thoracic cavity, and also aids in the elevation of the lower ribs.