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.
Physiology. Your intercostal muscles are located between your ribs. These muscles expand and contract to move your ribs, giving your lungs enough room to inhale and exhale. You have three layers of these important respiratory muscles â the external, innermost and internal intercostal muscle layers.hysiology. Your intercostal muscles are located between your ribs. These muscles expand and contract to move your ribs, giving your lungs enough room to inhale and exhale. You have three layers of these important respiratory muscles â the external, innermost and internal intercostal muscle layers.