In this early nude photography image, the woman appears to be freestanding. But if you look very carefully, there is a stand behind her in the shadow which helps her maintain her position. (Note that the mask not only provides anonymity, but also offers a simple device to provide the liberating experience without worrying who sees her.)
The stand behind her does not support her, but allows her to rest against it, and minimise any movement during the exposure. Some photographers were using exposure times of less than 3 seconds by the 1870s. But this was in sunlight. In a studio environment without good sunlight, exposures could take more than 5 minutes, at least in the early days.
This type of technique still has a place in the modern photograph where a position may need to be held for some time, such as in low lighting, where a wall may be used for street night photography particularly if a good depth of field is required.
Whilst not unique to nude photography, clearly, any such supports are more difficult to hide where there is no clothing. However, this can lead to some interesting creativity.