Erm....

Its hard to tell whether the reporter is in error or the author of the study; but they might've consulted a sleep-expert before drawing conclusions about dreams and motor-activity.

The reason REM sleep is also known as paradoxical sleep is that the brain is firing on all cylinders, as if it were awake. The commands for every physical activity your dream-body carries out are actually being sent, but dream paralysis is keeping most of the higher motor functions from being acted upon ( excepting eye-movement. )

When dream paralysis fails, we call it sleep-walking. Dream paralysis holding over into waking-up is a hallmark of night-terrors.

But we would expect someone dreaming of clenching their fist to send the same signal as someone who was actually clenching their fist. ( As distinct from someone merely thinking about it. )

Dante