Over the past month I've noticed the appearance of significant muscle wasting in my back side -- I mean, the gluteal muscles and the back of my thighs are turning to watery Jello!! I don't mean a little -- I mean a LOT, as if I've been on bed rest for 6 months.

I'm 58 and fairly active, riding about 100 miles+/week, plus some walking and gardening, and sometimes swimming and a little weight training. Nothing excessive, just consistent with 1-2 days off each week. I'm slender and maintain my weight through healthy eating and exercise. I don't sit around a lot, but in the early morning I enjoy reading at my computer while eating breakfast and drinking my coffee until about 7:00 when I change into my bike clothes or get busy around the house or garden. I enjoy knitting in the evenings after dinner, starting around 8pm until I go to bed about 10pm. This amount of sitting does not seem excessive, especially compared with the amount of sitting I did in my 25-year desk job which ended in 2011.

About two months I began waking up around 4am and having trouble getting back to sleep. Now I just get up and have my coffee and breakfast earlier and get on with my day. In addition, I also wake up around 1am to empty my bladder but usually fall back to sleep right away. So, I have a short and interrupted night's sleep almost every night.

As I stated above I began noticing this about a month ago, yet I am more active now than when I was working. I feel strong while riding and continue to make improvements in my strength and endurance.

I am wondering if this muscle wasting is due to lack of sleep to aid recovery, and/or lack of enough protein or other nutrition. It is significant enough to cause concern over my health - not vanity - and wonder if it could be a red flag.

Has anyone else experienced a sudden loss of muscle tone without explanation? What could be the cause of such a sudden change?