Well I would imagine it depends on the type of joint - it's a bit of a generalised question given that there are 6 types located throughout the body.
Running exercise, for example, will affect the synovial joint of the knee differently to the ball and socket type joint of the hip, surely ?
for a generalised question may i offer a generalised answer that will fit for all the synovial joints ... namely the production of synovial fluid will be increased, it if for this reason that we advice people to warm up gradually to give the joints an opportunity to produce the required fluid to effectively "grease" the joint for activity and thus protect the bones, cartilage etc from friction damage
was it this sort of thing you were looking for?