Here we are looking at Scale/Arpeggio-type shifts, to and from the thumb, within Thumbposition, meaning that the shift does not involve the placing (or removing) of the thumb from its position on top of the fingerboard. In other words, in these exercises the thumb is up on the fingerboard at all times: before, during and after the shifts.
The following practice material is offered:
SHIFTS TO/FROM THUMB WITHIN THUMBPOSITION COMPARED TO SHIFTS BETWEEN THUMB AND NON-THUMBPOSITION NOTES
In the above exercises we are permanently in Thumbposition. When however we shift between the thumb and non-thumbposition notes we will need to place (or remove) the thumb on (or off) the fingerboard, which is an additional complication for the shift that does not exist in the above exercises. This is why the above shifting exercises can be considered as precursors (preparatory training) for shifts between the thumb and other fingers in the Neck and Intermediate regions (non-thumbposition). Those latter shifts are looked at on a separate page (see below).
When shifting downwards from the thumb to non-thumbposition notes we are unable to remove the thumb before the shift because we are stopping the string with it. But In the case of shifting upwards to the thumb from non-thumbposition notes in contrast, the situation is the opposite. Here the placement of the thumb on the fingerboard is almost always done before the shift up, because this greatly simplifies the shifting process. This is why the distinction between shifting up to the thumb within thumbposition as compared to from the Neck and Intermediate regions, is quite artificial and almost unnecessary. In other words, we can consider shifts up to the thumb almost always to be shifts within thumbposition. This is why the practice material on the page “Shifting Between The Thumb And Non-Thumbposition Notes” provides us with much more very useful practice material for working on our shifts to and from the thumb in general.