TENS and NMES target different nerve groups of the body. TENS is specifically targets the sensory nerves, which are responsible for sending pain signals to the brain. NMES targets the muscle itself, specifically through the motor nerves. This allows the NMES machine to create a muscle contraction to recruit more muscle fibers when training; warming up or recovering. Sensory and motor nerves fire at different frequencies, which is why NMES and TENS devices affect the body differently.