F-waves and H reflexes are known as late responses. Late responses evaluate the entire nerve from root to the neuromuscular junction. Routine nerve conduction studies (NCS) only test the distal segment of peripheral nerves. F-waves represent the antidromic motor responses obtained following electrical stimulation of a peripheral nerve. They are most useful when the distal segment is normal and the proximal segment is abnormal. Measuring a longer segment allows detection of a proximal or diffuse problem, such as a demyelinating process. The F response is not an actual reflex; a reflex is a response that goes through a sensory component, synapses in the central nervous system, and then travels back down into the motor pathway. With F-waves, the pathway is from motor fiber to cell body and back to motor fiber.