Of exceptional muscle memory..

I am a naturally lean person, averse to any physical activity. I would, therefore, imagine myself having very little muscle mass. Irrespective, my muscle memory appears to be really active and sharp. Every muscle remembers every ache, every workout long after I have forgotten the routine and the gym instructor has forgotten my name. I know that I really need to do something about my creaking joints and stiffening limbs if I intend to rely on them for the second half of my life, the question is how!