Apparently they’re field testing (or just using) something that translates roughly to “pain-experiencer”, and those pads may be part of the apparatus, using electricity to let the user feel pain when activated. From my understanding they’re used to provide some degree of pain when one’s deemed injured or killed in an exercise. The goal is to add some additional realism to the experience
edit: in post #3835 there’s a picture of this apparatus in use. You can see a white pad on the soldier’s forearm, quite similar to what we see on the calf of the soldier in post #3840