Obese people may be more sensitive to pain
than people who aren't obese, a new study suggests.
All of the older adults who completed the study had osteoarthritis
of the knee, a disease that causes inflammation and extreme
pain in the knees.
Participants were given a mild electrical stimulation
on their left ankle to measure their pain reflex. The
stimulus was given before and after the participants took
part in a 45-minute coping skills training session that
included a progressive muscle relaxation exercise.
The obese patients showed a greater physical response
to the electrical stimulation than did the non-obese people,
both before and after the training session. This indicates
they had a lower tolerance for the painful stimulation
despite reporting, in questionnaires, that they felt no
more pain than non-obese people.
The relaxation procedure helped both groups cope with
pain,said Charles Emery, the study's lead author and
a professor of psychology at Ohio State University. Additionally,
our tests showed both groups had higher physical pain
thresholds after the relaxation session. But the obese
participants still had a lower threshold for tolerating
the pain.
Emery and his colleagues presented their findings on
March 4 in Denver at the annual meeting of the American
Psychosomatic Society.
The researchers wanted to see if coping skills training,
including progressive relaxation techniques would help
people with osteoarthritis to better cope with the pain
that the disease can cause. Also called degenerative joint
disease, osteoarthritis affects more than 20 million people
in the United States.
But they were particularly interested in seeing how the
obese group responded to pain; according to Emery, a small
number of studies have looked at pain sensitivity in obese
people, but many of these studies report conflicting results.
Some studies say that obese people are more tolerant
of pain, while other studies say they are less tolerant,
Emery said.
About a third of the study's 62 participants were obese.
Researchers determined who was obese based on participants'
body mass index (BMI) scores, which relates height to
weight. Obese patients in this study had a BMI greater
than 30 but less than 35. (Scores higher than 35 are considered
morbidly obese.)
The participants underwent two rounds of electrical stimulation
once before, and once after a 45-minute training session
where they learned different ways of coping with pain,
including instruction in progressive muscle relaxation
therapy.
The electrical stimulation came from an iPod-sized device
that delivered a slight electrical shock to a patient's
sural nerve, a nerve that extends along the ankle and
into the calf. This kind of electrical stimulation causes
sensations of tingling and mild pain in the lower leg.
The researchers determined the body's response to sural
nerve stimulation by measuring the reflex of the lower
leg muscles that surround the sural nerve. When the brain
senses pain, it sends a message to the body to contract
and move the muscles in order to get away from the source
of the pain.
This kind of evaluation is in some ways a more objective
way of measuring the body's response to pain, as opposed
to simply asking someone if they feel pain, Emery said.
But the researchers did ask participants how much pain
they felt. Participants completed questionnaires about
anxiety and pain perception after each round of electrical
stimulations. All participants, obese or not, reported
that they felt less pain after the relaxation session
than they did before.
Yet results of the sural nerve stimulus test showed that
the obese participants did not tolerate the painful stimulus
as well as the non-obese individuals.
Our findings show the importance of looking at objective
as well as subjective measurements of how the body responds
to pain stimuli, Emery said.
