hamstring cramps

Question
I am a natural body builder and avid wake boarder.  My hamstrings cramp a lot when I swim with my son.  I notice it more the leaner I get.  I am never over 12% body fat, and in the summer I can get down to 4%.  It is only my hamstrings, never any other body part.  Is there a way I can prevent this from happening?

Answer
Brad,
This is a great question.  Thank you for asking it.

Body building is designed to increase muscle and decrease fat.  You are also trying to make your muscles as dense/lean as possible.  Too much water in your muscles gives a slight "puffy" or "bloated" look to your muscles.  This isn't ideal for body building.

Unfortunately this goes against what is needed for swimming.  Swimming utilizes your long-twitch muscle fibers.  These are more endurance based.  They need water to help them flush out lactic acid and other toxins.  Swimming promotes longer and leaner muscles.  You may have noticed that Olympic level swimmers are never "ripped".  They have defined bodies, but they never get down into the 5-10% body fat range (usually).  This is because there is a certain level of body fat that is needed for the sport.

Ok, all that aside....

You can still enjoy swimming with your son, but you are going to need to stretch your hamstrings.  Your hamstrings are a large muscle group.  They are utilized for almost all let motions.  In other words, they are being worked almost all the time while swimming.  Since these muscles are not used to endurance type motions like swimming, they are over-worked.

Stretch your hamstrings prior to swimming.  Eat bananas (which have potassium).  Drink LOTS of water.

These should help you out, but just make sure you don't over do it.  Listen to your body.  Think about which is most important.  Swimming with your son is great, but you can't kill your hamstrings while doing it.

Best of luck.
Eric