Parasternal Muscle Adaptation To Mechanical Advantage Changes during Chronic Sternal Torsion

Neuromechanical matching exists in intercostal muscles, so that their most effective parts are the most activated. We investigated here this matching in the parasternal muscles (PS) and tested its adaptation after sternal torsion. In anesthetised 4‐week‐old rabbits, we attached the 2 nd rib to the bottom of the sternum with a thread. Six weeks later, the integrated EMG activity and mechanical advantage were measured in the medial PS of interspaces 2 to 5 bilaterally, at rest and during resistive loading. Activities were expressed in % of the activity obtained during maximal stimulations. Mechanical advantage was evaluated by measuring the passive fractional change in muscle length (ΔL/LΔV L ). EMG activity and mechanical advantage were compared to the values obtained in intact animals. Results are represented on the graph below.Changes in EMG activity are significantly correlated to the changes in mechanical advantage. So, after chronic torsion of the sternum in young rabbits, a modification of the EMG activity is observed that parallels the change in mechanical advantage.