Vagal tone, is the technical answer. A nerve (vagus) runs through your body and, among other things, slows the heart. When straining to "void", you cause that nerve to activate more strongly. It's also related to the Valsalva maneuver.
Vagal tone, is the technical answer. A nerve (vagus) runs through your body and, among other things, slows the heart. When straining to "void", you cause that nerve to activate more strongly. It's also related to the Valsalva maneuver.