Weinreb and Friberg conducted surveys on two groups of research subjects: 12 people who already had glaucoma and 16 other volunteers, all of whom were from 19 to 40 and had no eye problems or disorders linked to vision difficulties. Under controlled conditions, each research group was allowed to hang upside down while doctors measured blood pressures and other data designed to gauge whether the sudden and extreme flow of blood to the head that occurs in inversion brought about potentially dangerous increases in pressures on blood vessels in and around the eye.
Increased pressures were noted in both groups, though the measurements returned to normal soon after the subjects returned to a normal position. Though the results are clearly labeled as tentative, Friberg and Weinreb were concerned enough with what they found that, in both studies, they made recommendations similar to the conclusion in the one to be released today:
"Inverting for extended periods of time or performing strenuous exercises in this position could prove hazardous. We therefore discourage those with (a variety of) ocular conditions from participating in inversion activities."
Backers of the practice were quick to defend hanging. Gravity Guidance's Martin, for instance, contended that the new research is only tentative and preliminary--and, moreover, that it is contradicted by the experience of inversion partisans.
Martin, who maintains a rehabilitation medicine practice in Pasadena, said he has had a number of patients in their 80s and 90s who have done inversion exercise without ill effects and that, in fact, no patient in his experience has ever suffered an eye problem associated with hanging.
"What (the new study focuses on) is possibilities," he said. "It's like me walking across the street. I \o7 might\f7 get killed. It becomes so theoretical. I think they are going to have to reorganize their research.
Another Boot Backer
"Over a period of time, you'd think we would have had all sorts of retinal and glaucoma problems, yet we've never had one."
Martin quickly added, however, that any would-be hanger with glaucoma, sickle-cell anemia, high blood pressure or diabetes should be certain his or her condition is well controlled by drugs before taking up the exercise. Other boot backers have said they recommend any person with a pre-existing eye condition who wants to participate in inversion should obtain approval from his or her ophthalmologist beforehand.
Adding to the confusion are two other studies that recently appeared in the journal Physician and Sports Medicine--itself a prominent publication--that tended to discount any prospect of eye damage associated with gravity boot inversion. Both studies were conducted by Dr. Robert Goldman, a Chicago osteopathic physician and a gravity boot enthusiast.
In one of the studies, Goldman concluded people with uncontrolled high blood pressure should not indulge in inversion because existing hypertension would be exacerbated to possibly dangerous levels.
Goldman said he had noted increases in ocular pressure readings when he first started doing research in the field, as well, but that he concluded the elevations weren't dangerous because the readings quickly return to normal when the patient returns to the normal standing or sitting position and because the physiology of the skull provides some protection against eye damage by acting a little bit like a restraining cage.
"I don't think there is really much of a risk to the eye," Goldman said. He said that today's inversion backers recommend against simply hanging upside down without moving for long periods of time, anyway, preferring equipment that permits a hanger to move around and, preferably, to rotate back up to a straight position frequently during a hanging session.
Special equipment has been in common use for several years that permits a hanger to lie back on a sort of couch and rotate to the upside down position--and back to normal--at will.
"The message," Goldman said, "is that you should listen to your body and pay attention to how you feel."