Optimal Muscles for Evaluation of Recruitment, Motor Unit Configuration, and Interference Pattern

In general, flexor muscles such as the tibialis ante­rior and the iliopsoas are useful for the evaluation of MUAPs and recruitment in the lower extremity. These muscles can be activated by tickling or pinch­ing the bottom of the foot, producing a withdrawal response. In the upper extremity, the flexor digito- rum sublimis and biceps muscles are often reflex­ively activated by the newborn or young infant. More proximal muscles can be activated by moving the extremity or positioning it to produce antigrav­ity stabilization of the limb by the firing of prox­imal musculature. Alternatively, reflex posturing techniques such as the Moro response can be used to activate the shoulder abductors, but are usually not necessary.