After they had dined, Mrs. Teachum told them she thought it proper that they should use some exercise in the cooler part of the day, lest, by sitting too much, they should injure their health. – Sarah Fielding (1710–1768), “The Governess, or The Little Female Academy,”

I believe most distempers proceed from too much sitting still. РMarie de Rabutin-Chantal, letter to her daughter Fran̤oise-Marguerite de S̩vig

Helen started, and said she feared she had been sitting too long idle. – Maria Edgeworth (1768–1849), Helen, 1834

Throughout the illness the most obviously exciting cause of the attacks was posture, stopping over a writing-desk; and he ultimately had to do such work either kneeling or at a standing desk. – Lawson Tait, 1882