Recently I've been modelling my kick serve in the Edberg way, with quite an arch back. And paired with a very fast racket head speed, I'm getting the desired amount of head speed. However, I woke up (after playing a doubles match last night) this morning and my lower back was very stiff? Is it likely to continue or will this go away as I continue to serve more and more in this way. I know it's a difficult question to answer, but what do you guys think?