Mako Vunipola says his father’s tough love and the family’s strong genes have enabled himself and brother Billy to return from injury for the final two matches of England's Six Nations campaign.
The Saracens forwards have overcome knee injuries in time for the climax of the Six Nations matches against Scotland and Ireland, beginning with Saturday's Calcutta Cup clash at Twickenham.
Mako appeared as a replacement against Italy in round three, while Billy has defied predictions that he would miss the entire Championship by returning from surgery three weeks ahead of schedule.
While acknowledging the genes that have aided a swift recovery, Mako also believes the stern attitude of his father and former Tonga international Fe'ao Vunipola helped develop resilience in England's bulldozing siblings from an early age.
"We're very lucky in terms of healing quickly, but also part of it is that when we were growing up, dad wouldn't accept that we were hurt in any game," said Mako.
"If we went down with a dead leg or something like that, he would say it wasn't a real injury.
"It comes from our granddad, who would always joke that if we broke a leg he would just buy a new one anyway.
"That's kind of the mindset that we have. If either of us go down, the other one will come over and say 'get back up'.
"I don't want to say we're the toughest men ever, it's more that we don't want to show a weakness to the other brother."
Billy made a successful comeback for Saracens against Newcastle on Sunday and his availability will be welcomed by England, who have sorely missed their most devastating ball carrier in this Six Nations.
Mako views his younger brother's rapid return as evidence of the growing maturity of a player who in the past has struggled to keep his weight down due to a poor diet.
"I've had a few knee injuries before and knew there were no shortcuts for either of us, so for Billy to get back early is a credit to him and the staff at Saracens and England," Mako added.
"It's surprising how well he's moving and in training he looks up to speed as well. It's good to see him back doing what he loves.
"The maturity he's showing is something that comes with experience. He's getting a bit older now and he knows the body is only as good as the work you put into it.
"He's learnt that the hard way and he's put in the hard graft now with this injury and done all he's needed to."