Unfortunately this situation can be caused by many outside forces & JofNile has dealt with a few of those issues that could have resulted in this.  Granted exercise is a key assister but when muscle is acted upon adversely it doesn't have great results.  
Bestus wishes  Jo  

To put things partially in perspective     SHEESH      my mind keeps telling me I'm 19 yrs of age, my body says & reacts to the age of 29     GOODNESS  those  ten years took a toll.  Now for those over 29   Hmmmmm !!!