BACK PAIN DURING 6-DEGREES HEAD-DOWN TILT APPROXIMATES THAT DURING ACTUAL MICROGRAVITY

Astronauts often experience back pain during spaceflight, Retrospectiv ely, Wing et al, (14) found that during spaceflight, 14 of 19 Shuttle crewmembers experienced back pain, which they described as dull (62%), localized to the lower back (50%), and with an intensity of 2 on a 5- point scale, Further, the spine lengthens 4-7 cm in microgravity. Our objective wets to compare back pain and spinal lengthening (body heigh t increase) during simulated microgravity (6 degrees head-down tilt, H DT) with the same parameters during actual microgravity. Eight male su bjects completed ct modified McGill pain questionnaire with intensity graded from zero (no pain) to five (intense and incapacitating pain) e ach day tit 7:00 pm during 2 d pre-HDT control, 16 d HDT, and 1 d post -HDT recovery periods, Also, the subjects' heights were measured each day while supine (control and recovery) and during HDT, Back pain incr eased from zero (pre-tilt control period) to 2.3 +/- 0.4 at days 1 to 3 of HBT, and was categorized as dull and/or burning pain in subjects' lower backs, Only 2 subjects reported any pain after day 9 of HDT and during recovery, Heights increased 2.1 +/- 0.5 cm by day 3 of HDT and remained at that level until the end of the HDT period, Although spin al lengthening in space is greater than that during HDT, the HDT model approximates the level, type, distribution, and time course of back p ain associated with actual microgravity. In the HDT model, pain subsid es in intensity when spinal lengthening stops, Therefore, back pain in actual and simulated microgravity may result from stretching of spina l and/or paraspinal tissues until a new spinal length is reached.