[Source] She [Dr Jenny Pynt] pointed out a few other categories that often spell trouble, recommending against stools and other seats without backrests, at least as full-time accommodations, “because no matter how virtuous you are, you will slump.”
Although I can infer that virtuous is intended to mean physically upright or plumb, I consulted the ODO and Merriam but see no definition connoting anything physical?