It's 10 am and Xin Xin, now 27 years old and 102 kilograms (225 pounds), walks slowly down a corridor to begin her daily training routine.
She is one of two giant pandas at the Mexican capital's Chapultepec Zoo, which is home to the only members of that species worldwide that are not owned by the Chinese government.
Away from the gaze of the zoo's paying customers, Xin Xin undergoes a conditioning program every day under the supervision of her trainer, Ulises, and a zoo veterinarian, who offer her an apple - one of her favorite foods - provided she allows them to examine her with a stethoscope and brush her.
After Xin Xin's routine is finished, Shuan Shuan, who is about to turn 30 and weighs 114 kilos, has her turn.
"It's a conditioning program focused on allowing essential medical interventions," the director of Mexico City's zoos, Claudia Levy, told EFE.
She said that during the training routine the zoo's team simulates the extraction of blood and X-rays. The idea is to get the bears accustomed to these procedures and ensure that thorough medical tests are stress-free.
Thanks to this daily routine, the pandas establish a bond of trust with the zoo employees and will not need to be anesthetized or coerced into undergoing medical exams when the time comes.
Even though Shuan Shuan is Xin Xin's aunt, the two are in separate compounds because giant pandas are solitary animals and could harm one another if they lived together.
The care they receive has allowed these giant pandas - the oldest in the world outside of China, where that species is endemic - to approach the very advanced age of 30.
The connection between Mexico City and pandas dates to 1975, when the Chapultepec Zoo received two pandas as a gift from the Chinese government: a male called Pe Pe and a female who was given the name Ying Ying, both of whom died many years ago.
But that history has an uncertain future because Shuan Shuan - the daughter of Pe Pe and Ying Ying - and Xin Xin - daughter of Tohui, one of the original pair's cubs - both are too old to reproduce.
Tohui, the first naturally conceived panda to be born in captivity outside China, was the most popular and famous panda to live at the Chapultepec Zoo.