An interesting article in the ‘Proceedings of the National Academy of Sciences’ (Vol. 96, #14, 7752-7755, July 6, 1999, http://intl.pnas.org/) describes the discovery of a gene (now called ‘mu gene’) which modulates the opiate receptor density of nerves in mice as well as humans.
In other words: some folks have a high receptor density for internal pain suppressors and therefore might have a much higher pain threshold – i.e., they can tolerate pain much easier than others. Whereas some folks – who do not have this mu gene, or where it is not activated – will jump to the ceiling at any manual treatment pressure above a few hundred grams.
Flimsy speculation on my part: maybe folks with an active mu gene and a high pain tolerance will also tend to respond well to the analgesic effects of acupuncture or other endorphin-related treatments.
What to do if we have a client with a very low pain threshold? Let’s be more careful about blaming them or their environment (“trauma in the past,” etc.). It could be that because of purely genetic reasons they might not respond so well to (i.e.. feel tortured by) any strong pressure work.
Nevertheless, local differences in pain sensitivity within the same individual might need a different explanation.
(Editor’s note: see also http://www.sciam.com/explorations/1999/072699pain/)