Abnormal peripheral action potential amplitude Decreased compound muscle action potential amplitude 2021-01-02T12:41:56Z Reduced level of the compound muscle action potential (CMAP), which is recorded following electrical stimulation of a nerve from surface electrodes overlying a muscle supplied by that nerve. The CMAP is a summated voltage response from the individual muscle fiber action potentials. The CMAP amplitude is measured from baseline to negative peak (the neurophysiological convention is that negative voltage is demonstrated by an upward deflection) and measured in millivolts (mV). Decreased CMAP amplitude