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.
The intercostal muscles lie between the ribs. When you exhale, these muscles contract, and in conjunction with the abdominal muscles, the lungs contract and air is forced up v â¦ ia a positive pressure gradient.here are three levels of intercostal muscles all situated between the ribs. The layers are named according to depth into the thorax, the outer (or external) intercostal being the most superficial the inner (or internal) intercostals being in the middle and the innermost intercostal being the deepest.