Table 9.

List of the selected papers that referred possible limitations either in the validation of the systems or in their use.

Concerns	Reference
Battery levels	[2,3,11,13,15,29,31,35,51,61,65,66,70,77-79,83,91,93]
Privacy	[2,3,34,35,51,61,65,69,70,78,79,87,91]
Developed models	[1,2,15,35,70,76,88,94]
Smartphone body position	[1-3,6-13,15,26,27,29,30,34,58,59,75,83,84]
Recommendations and feedback	[29-31,51,55,57,59-61,65,77,78,83,88,90-94]