I've noticed two cycles in my gym, the yearly mesocycle and the weekly microcycle.
The yearly is fairly obvious, when it gets cold, people go to the gym, when it's warm they're outside more.
When the new year rolls around, LOOK OUT. Same with spring and summer breaks.
Then there is the weekly cycle.
Everyone over-eats on the weekend and feels guilty enough about it to go to the gym.
By the end of the week they're over it and stop going.
Friday's are a ghost town in my gym.