In the world of heavy equipment, part of that learning means memorizing how to use levers, joysticks, and even pedals in a coordinated way to control the attachment at the end of the boom.
But how does this memorizing take place?
At first, you need to concentrate in order to make your fingers, hands, arms (and feet) move in just the right way, based on what you see. What you're learning is precision, i.e. how to make the boom attachment perform the task (move a load, grapple a tree, drill a hole, etc.) carefully.
(Scientists have discovered that there are a large number of internal brain structures, which work together with the input and output brain structures to form fleeting images in the mind. Using these images, we learn to interpret input signals, process them, and formulate output responses in a deliberate, conscious, way.)
But after a while, the "seeing-thinking-doing" gradually becomes "seeing-doing" because your muscles seem to "know" and "remember" just what to do. What you're learning now is speed, i.e. how to perform the task carefully and quickly. That's muscle memory.
Scientists call this "kinesthetic memory" or "neuro-muscular facilitation" and they speak of "sensory-motor" learning, since you are combining sensing input, i.e. what you see with your eyes, with motor output, i.e. what you do with your body.
Of course, during the "drill-and-practice", your muscles aren't really memorizing anything (since all memories are stored in your brain). Instead, what you see with your eyes is interpreted by your brain in the form of nerve signals to your muscles to make your body move.
Now by making the same movements in response to the same visual cues over and over again, the associated nerve-muscle connections gradually become more effective, i.e. the transmission of the signals becomes more effective, and this is how the "thinking" in the "seeing-thinking-doing" is