In the world of Shadowrun the sim module required for VR manipulates the reticular activating system into making the body go limp to avoid damage to the subject while in VR.
In SR4A it was relatively easy to disable the so-called "RAS override" of a commlinks sim module, which would allow you to go into VR while maintaining neurological control of your body. From page 328 of SR4A:
"As a safety precaution, sim mods override your motor functions while you are fully immersed in VR/simsense, so that you don’t blindly thrash around in the real world and potentially injure yourself or break things. This means that your physical body is limp while you’re online, as if you were sleeping. This reticular activation system (RAS) override can also be disabled with a Hardware + Logic (5, 1 hour) Extended Test, at the user’s own risk."
In SR5, the RAS override is mentioned in conjunction with BTL chips (specifically, mood, personafix, and tripchips) on page 413;
"The RAS override feature is frequently disabled so that users can move around freely under the influence of the chip."
In the real world, the RAS control sleep more than motorfunction if I remember correctly, so the function attributed to it in Shadowrun is most definitely pseudo-science, but I wouldn't worry too much about it. There is definitely precedent for being able to immerse oneself in VR while maintaining some degree of physical control.
Earlier novels often describe deckers as typing on their deck while in VR, meaning motor control would most certainly be necessary.