It seems that sit-ups are still something people in Japan are encouraged to do, though most exercise experts now discourage sitting-up in favor of stomach crunches.
@Lilliwyt—
The question is a bit
out-of-the-blue, but the sit-up could be seen as representative for exercise more generally, and the question was asked by one girl and of another who are at an age in which their physical fitness is institutionally tested. So it's
somewhat as if one girl asked the other if she could make any sense out of the quadratic equation.
Further, if these two were in the same room, questions out-of-the-blue would seem less odd and, in an age of mobile telephony, telephonic conversation becomes increasingly like conversation held in the same room.
By the way, I find it a bit unbelievable that the girl could not do even one sit-up, and yet could play table tennis.