Sustained speed may be estimated by calculating the drag of a simplified model of the body, that can be approached by a prolate spheroid, and the sustainable level of energy output by the muscles. A first study of this problem was published by Judy Massare in 1988. Even when assuming a low hydrodynamic efficiency of 0.65, Massare's model seemed to indicate that plesiosaurs, if warm-blooded, would have cruised at a speed of four metres per second, or about fourteen kilometres per hour, considerably exceeding the known speeds of extant dolphins and whales. However, in 2002 Ryosuke Motani showed that the formulae that Massare had used, had been flawed. A recalculation, using corrected formulae, resulted in a speed of half a metre per second (1.8 km/h) for a cold-blooded plesiosaur and one and a half metres per second (5.4 km/h) for an endothermic plesiosaur. Even the highest estimate is about a third lower than the speed of extant Cetacea.