please help me....numbless at upper back of my legs while in sitting position?

Such kinds of pain generally may have one of two causes. Ciruclation compression number one, or nerve compression number two.

Nerve compression is the more difficult to resolve. Perhaps you should not sit so much?

Sometimes a massage helps. had leg pain a yr ago and when i walked at 2 miles my leg would burn and pain. Had one 30 minute professional massage and I could 3 miles and had an hr massage and the problem was gone.