Some ink companies make "stretch" products, particularly white (Rutland at least used to make a Spandesol White I belive). But in a pinch just add 10%-15% of HD clear if you have it around. It has terriffic elongation properties. This best suited for ribbed fabrics, Spandx, Lycra etc. For Dry fit stretch fabrics add to a poly white and over print with standard colors. We always keep a gallon of stretch white in the ink department.
Just an FYI tp
