my 5 year old is what i would describe as cold backed... before i ride i often either put his equissage on (equilibrium do a cheaper version) to warm up his muscles/ pop him on the lunge for 10 mins. i always do loads of work in walk before trotting- at least 15 mins of leg yielding and walk-halt trans and shoulder in and stuff. seems to work (most of the time)
One of my horses is the same, he's slightly cold backed. I find him much looser and less stiff when he's ridden daily, walked around for a while before warming up and rugged up nearly all the time.
Hope this helps