When did this idea/tradition begin?
I can see it being useful for Marathoners / Half Marathoners, because most of us follow a weekly or a 14 day type schedule, and Marathons / Half Marathons are nearly all on Sundays.
But why do so many 800/1500 people do this? Or even 5k/10k people?
I train for 5k, and I like to do 5x1000, 4x1200, 3x1600, 6x800 type stuff on Sundays. Because I am following a weekly schedule, and races are often on Sundays, it makes sense to me to do "race simulation" stuff on Sundays.
But you should see the funny looks from fellow runners when I tell them I'm doing this on Sunday, or I ask if they want to join in.
"Oh no no no, good heavens, Sundays is for long runs."
But why?