Been there, had that.
If you find yourself ramping up the miles suddenly, body aches ensue.
I was training a couple years ago building up my miles. From 6, 10, 12 then 18-22 miles per session. When i broke 18, things started to breakdown. Tendonitis, rotator cuff injury and wrist problems.
Solution, ramp up the miles slowly, practice proper paddling technique (use your back, legs and torso, not your arms), find the proper paddle length, use an adjustable feather paddle (60 to 65 degrees is generally good) and adjust it so that you dont have to twist your wrist so much. The paddle should be feathered such that when your twist you torso and put the forward paddle down in the water, the paddle face should be ready for the power stroke without having to twist your wrist. This is only achievable with proper paddling techniques as below....
http://m.youtube.com/index?desktop_u...&v=DnUVLDGIgiw
For a lot of us kayak fishermen, paddling is an after thought. Sadly, for me at least, age in an unforgiving mistress. Better technique and training will minimize injuries.