Back pain during 6 degrees head-down tilt approximates that during actual microgravity

Astronauts often experience back pain during spaceflight. Retrospectively, 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 was to compare back pain and spinal lengthening (body height increase) during simulated microgravity (6 degrees head-down tilt, HDT) with the same parameters during actual microgravity. Eight male subjects completed a modified McGill pain questionnaire with intensity graded from zero (no pain) to five (intense and incapacitating pain) each day at 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 increased from zero (pre-tilt control period) to 2.3 +/- 0.4 at days 1 to 3 of HDT, 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 spinal lengthening in space is greater than that during HDT, the HDT model approximates the level, type, distribution, and time course of back pain associated with actual microgravity. In the HDT model, pain subsides in intensity when spinal lengthening stops.(ABSTRACT TRUNCATED AT 250 WORDS).