Burger - with 85 tests, the most capped player in the Proteas team - wore a GPS tracking device during the team's training clash with New Zealand A and was startled by the results.
When she played in the recent SPAR national championships, she covered an average of 3km per game. But against the New Zealand side, she clocked up around 9km in the three quarters that she was on court.
"It was something I was interested in finding out - just how fit I am, and how I could better that," said Burger.
"And it's very interesting that it revealed exactly what we lack - the intensity in our game. We are used to training long, but not that intense."
Plummer said the disparity in numbers is revealing.
"It was difference of the intensity, plus they still overwork. We are trying to expose them to standing next to the player, take on the body and take the ball. You don't have to run over there, come back here, to drop back and go forward for the ball. So they make about four or five moves before they get the ball. We're teaching them to be far more competitive on a one-on-one basis in an attacking situation," the two-time World Cup winning coach said.
"[Burger] has been in the Proteas for a long time. But as you get older you have to work harder to stay fitter. So she's taking this opportunity to wear a GPS. We didn't know it at first, but I think its fantastic that a player wants to make sure she is going to be able to cope with things."
Despite copping a heavy 68-43 loss to Australia in the weekend's opening match, Plummer was pleased with her side's first outing, having reduced the difference between themselves and the world No 1 side by 10 goals since their last meeting at the 2015 World Cup in Sydney.
"I was really quite delighted, from world champs till now, with the improvement I can see, and the commitment and the effort," Plummer said.
"We want to be defined as a team that's going to take it up to the top sides, and we're only going to learn by actually being in this competition. So we have to learn about how much tougher and how much more contesting we have to do, and how much more consistency we have to have."
Few would have predicted ahead of last weekend's double-header that the Australia v South Africa test would have been closer than the Silver Ferns v England test that followed - albeit by one goal.
The Ferns are seeking another dominant performance in Hamilton tomorrow, as they look to consolidate their combinations ahead of Sunday's finale against Australia in Melbourne.
Netball Quad Series:
7.45pm Silver Ferns v South Africa, Claudelands Arena, Hamilton.
9.30pm Australia v England, Adelaide Entertainment Centre, Adelaide.
