Hi Clare, My understanding has always been ( and please anyone correct me on any of this) : They all cause neuromodulation , but how depends on the parameters. When using TENS for OAB via tibial nerve the parameters ( mainly Hz) are quite different to when you use NMES for muscle contraction. It is also used on continuous mode as compared to a work/rest function which is really the simplest way of explaining the difference. Most research uses 10Hz for OAB although some goes up to 20 Hz , You won't get a tetanic contraction at 10 Hz , rather a flickering, but the idea is to take the mA up until you get twitching to ensure you have you electrode placement correct ( over tibial nerve) then turn down the mA until current is comfortable but not causing contraction. If you put the electrodes on yourself and play with the Hz you will feel (and see) the difference in contraction quality. Also with lower Hz you tend to get more of a sensory effect ( which you want with OAB ) but will get motor if mA is high enough. When you stim the pelvic floor for contraction you are using the higher Hz as you say and that is what gives a tetanic contraction ( up to a point , past about 50Hz there is no time for depolarisation so contraction drops off and you get more of a sensory effect again.) Plus you are using a work/rest parameter as you don't want a continuous contraction! The pulse width general rule is wider it is the deeper it goes and can be adjusted for comfort but the wider pulse is less comfortable. I think too many people just use the pre-set programs on the machines without having a play with the parameters via the custom programs to individualise them for the patient and when the preset doesn't work they give up saying stim/TENS doesn't work. I also think as physios we tend to use TENS and E-stim as a 'last resort' when we should be employing them much earlier in pelvic floor rehab in particular ...but that is my little soapbox!