Unless I’m mistaken (and that’s quite possible!), this should be trivial to test. Sous vide some meat for an overly long time to a precise temperature, then cut each piece at set intervals.
Another important effect during cooking is the breakdown of collagen fibres (present in tough connective tissues which make some cuts of meat very tough to chew). This occurs in the presence of moisture at temperatures above 170F. When collagen breaks down the meat tenderizes and the collagen itself turns into gelatine which absorbs moisture and retains it within the meat. A gelatine-rich cut of slow-cooked meat (such as oxtail) can be very sticky and packed with flavour. This is one case where food can taste juicier with longer cooking times.