"Niki was always two to three kilos too heavy. It's not that Niki was fat before, but those two lost kilos make the difference between being able to win or ride in the final," team doctor Yvan Vanmol told Sporza.be.
The Quick-Step Floors website has Terpstra listed at 75kg and 190cm, a two kilogram loss represents less than three per cent of his total bodyweight, which Vanmol contends was useless fat and not muscle.
"Niki was just too heavy in previous years, he had too much fat," Vanmol said. "Fat does not pedal, it's only a load you have to drag around."
There has been much discussion of extreme weight loss among Grand Tour contenders, their skeletal appearance perhaps sending the wrong message to aspiring young cyclists who then try too hard to slim down and risk developing eating disorders.
Vanmol doesn't want to send the wrong message about the importance of losing weight. "I have always avoided being fanatical with weight," he said. "The boundary between normal control of your weight and developing a pathological eating disorder is very thin.
"I will definitely not go far in promoting the ideal weight or slimming. In my 30-year career, I have seen enough problems with people who were fighting so much with their weight."
Vanmol said that Terpstra didn't do anything special to lose the weight, other than to eat less and skip some desserts. He came to the first team camp in December two kilograms lighter and has kept it off.
"There is nothing more to it, that has not been a challenge: it is common sense: two kilograms less can make an essential difference in a race with a lot of climbs." Vanmol said.
Terpstra, now 33, won the 2014 Paris-Roubaix, and followed that victory with others in the Tour of Qatar and Tour de Wallonie in 2015, and Le Samyn and the Eneco Tour in 2016. He finished third in the Tour of Flanders behind teammate Philippe Gilbert but went winless last season.
"Last year Niki had a very difficult year, mainly due to bad luck and falls, but he also realized that something could still be done about it," Vanmol said.
Vanmol says that Terpstra could still lose half a kilogram without shedding muscle, but acknowledged that Classics riders are resistant to getting too thin for fear they would not be able to withstand the cold temperatures.
Terpstra's win in Le Samyn this season in freezing temperature proved that he hasn't gotten to that razor's edge, Vanmol says, and he doesn't really need to. "I think he is at the critical weight where he can climb well enough for these races and still has some protection against the cold."