Flat feet is a phenomenon where there are no arches or knells on the feet, hence the term "flat feet". Regular running or vigorous exercise can hurt the delicate feet and wear them out.
However, the latter reason is no longer valid. Recently, specially designed sports shoes have been introduced in NS. The shoes are designed to cushion the shock on the feet during vigorous exercise.
So now, there is no more danger of NS men in falling flat on your feet.
Crystal Tein, The Cheers News