People tell me that they don't have time for a shower in the morning. They take their shower at night, before bed. I marvel at this. If I couldn't take a shower in the morning to relieve my stiff muscles, it might take me until noon to get going. Even then, I might need more than my one cup of coffee to feel as if I was in the land of the living.
I know I am not the only one who wakes up stiff in the morning. For those who get up and feel as if they are the Tin Man out of the Land of Oz, you have my heartfelt sympathy, as I am right there with you. I have fibromyalgia, and while this might not be the sole reason I am stiff in the morning, it probably doesn't help.
What does help is being able to go from my bed to the shower. As I feel the warm water running down my body, I can feel my muscles and their tensions start to relax. It is a feeling that I cherish every single morning. Usually, by the time I have finished all my showering, I can at least feel as though I might live, after all.
In a chiropractor's office, sometimes they will put warm towels on your back to relax the muscles before they work on you. It's the same thing. I don't know what makes "warm" relax the muscles, but it does.
So, this is just a suggestion that if you are stiff in the morning and you are an evening shower person, try changing your shower schedule for a few days and see if it helps. Some people say they do not want to go to bed "dirty." If that is your issue, too, do two showers, making both of them a bit less intense. You might find it helps your sore, stiff muscles a lot in the mornings.