leg spasms?

Question
HI there,

Ive got a brain buster of a question for you.  I have an Australian Shepard, Pit-bull mix dog about 1.5 years old.  He is in great shape, perfect weight, and runs about 70 miles a week with me.  

My question is this:  When we get home from vigorous runs, or play fetch or chuck-it in the yard, right after stopping his hind legs are still shivering or spasming like his muslces are still freakin out!  Its been in the 50's. 60's nd 70's lately and regardless of temp it still happens.  

It stops soon after the games and runs end, it lasts for maybe 5-10 minutes.  

He is not under or overfed and is in great physical shape.  He also gets no table scraps or people food of any sort.  

He is not in any discomfort when this is happening, it just looks like he is not ready to stop playing and is still jazzed up!  If you grab his shaking leg it usually either stops for a second or just quivers while you hold it.

Do you have any ideas what this is all about and if it is harmful to him.  Like I said, he doesn't seem to mind and I have seen to adverse reactions to any of his exercise.  No limps, no soreness.....nothing.

Hope you have an idea and can't wait to hear back from you!

Nolan Taylor
runningrock@hotmail.com

Answer
This is pretty common in all types of dogs. The shaking isn't necessarily linked only to exercise, but also when dogs are excited or tense.

It is thought to be due to incomplete mylenization of the nerve sheaths. Myelin is the "insulation" around the nerves. The muscle bundles "fire" when not necessary, causing the mild tremors. Other than being an odd side effect of exercise, it should not cause any health related concerns.