The corresponding nerves on the other side of the body may be studied for comparison. Nerve conduction studies are usually done before an EMG if both tests are being done.Nerve conduction testing takes 15 minutes to an hour or more, depending upon how many areas are studied. Nerve conduction studies show whether the nerves transmit electrical impulses to the muscles or up the sensory nerves at normal speeds (conduction velocities). Sensory nerves allow the brain to respond to pain, touch, temperature and vibration. Different nerves have different normal conduction velocities. Nerve conduction velocities also tend to decrease as a person gets older. Slower conduction velocities may also be caused by injury or damage to a nerve (such as carpal tunnel syndrome) or group of nerves (such as Guillain-Barré syndrome or post-polio syndrome).