Optimal Muscles to Study for Rest Activity

In evaluating an infant or young child for a general­ized disorder, specific muscles are chosen to permit

Figure 7.5 Phrenic nerve conduction study in a 13-year-old child with C2 traumatic spinal cord injury.

evaluation of insertional and spontaneous activity. The distal hand (first dorsal interosseous) and foot muscles of infants usually have minimal voluntary activity due to immature motor control at this devel­opmental age, making them good sites to assess spon­taneous activity. In addition, extensor muscles such as the vastus lateralis and gastrocnemius in the legs and the triceps in the upper extremities are useful sites for the evaluation of insertional and spontane­ous activity.

In the neonate and young infant, foot and hand intrinsic muscles exhibit high levels of end-plate noise because of the relatively larger end-plate area in the immature muscle. This end-plate activity may be con­fused with fibrillation potentials. Fibrillation potentials and positive sharp waves are not typically observed in the full-term normal newborn.