IF-4000 Muscle StimulatorIF 4000 Interferential Muscle Stimulator Professional Pain Relief at Home or in Clinic Target Inflammation. Relieve Pain. Accelerate Healing. The PMT IF 4000 Interferential (IF) Muscle Stimulator delivers low frequency therapy using two medium frequency currents that intersect to create a therapeutic beat frequency (1250 Hz). This closely matches the bodys own natural electrical signals, making it a highly effective option for pain management and