I see emotional purity as the root of physical purity. The more emotionally connected you are with someone, the more you are (or desire) physical connected!
A few years ago I weeded a garden as a work project with some friends. Well, we didn't weed the garden, we just basically trimmed the weeds. I remember when we were all done thinking that: yes, the garden did look a lot better, but I knew we didn't get all the roots so it would be just as weedy in just a matter of months.
We all have heard that God's Words directs us to remain physically pure for the marriage relationship, yet at the very core of staying physically pure is a deep conviction to remain emotionally pure.
Once a couple begins to attach emotionally; physical affection is naturally going to follow. This is even true of friends. Once you get to know someone better (even someone of the same gender) you may be more willing to give a hug, pat on the back, touch them when you talk...ect. These are all non-sexual ways of touching, but most of us are not this way with people we don't know.
So in opposite sex friendships a guy and girl can become emotionally close and start having long extended hugs, hand/food/back massages, kiss on the forehead or cheek, or cuddle together. This may be just "friendly" physically contact, but this should be saved for a committed relationship.
What would you think if you saw a married woman cuddling with her best friend's husband or giving a back massage to a co-worker? If you would not do these things as a married person, why do them while you are single?
In my book I give the plumbline questions I asked myself when I was single in order to maintain emotional purity. One of those is: Would I treat him this way if he was a married man? So if you are questioning your own "physical" contact with a friend ask: would I do this if he were married?
In Christian single circles I have seen how these "innocent" physically interactions are very common and accepted. Our bodies belong to our mates, not our friends.
I found that remaining physically pure for my husband a whole lot easier once I committed my life and my heart to emotional purity!