PhotoRead the whole book in one go first time.
One way to get around the sore arm, stiff neck is to place the book on your thigh with perhaps a cushion under it. Sit in a comforable chair with an armrest. Allow your lower arm to be supported by the arm rest as you turn pages. This takes the weight off the shoulder so you're less prone to sore arm and stiff neck. A cushion helps so you don't have to lower your head too much.
We were photoreading between 5 and 10 Books in a 30 minute period all up we averaged between 20 and 40 books each that day. We all shifted and moved as necessary for the comfort of our bodies. Like with regular reading change postition, don't think about just keep going.
When it comes to activating the textbook. PhotoRead the section you want to activate and 2 chapters before and 2 chapters after it again. Focus on activating a chapter at a time treating each as a book in it's own right, after the first activation of about 30 or less where you go from cover to cover, you're noticing familiarity and layout etc you looking ofr much detail in the first activation. The PhotoReading the whole book and first activation of the whole book is to lay the foundation of having the whole available to you while you activate the parts.
AlexK