ESTIMATION OF ELBOW JOINT POSITION BEFORE, DURING, AND FOLLOWING A 17-DAY SPACEFLIGHT.

Abstract

1920 The ability to estimate elbow joint position was tested in four male astronauts before (-30 and -12 days), during (1, 4, 9, and 15 days), and after(+1, +5, +9, and +16 days) a 17-day spaceflight (STS-78). Subjects were asked to estimate 90 ° or 135 ° joint angles during passive (relaxed) and active (10% maximal agonist effort) isokinetic extension (EXT) and flexion(FLX). Subjects also estimated these joint positions during low resistance isotonic EXT. For each angle, 6 (isokinetic) and 3 (isotonic) trials were requested in random order. Across all test conditions, the mean angle estimate ranges were 93 °-118 ° and 119 °-152 ° for requested angles of 90 ° and 135 °, respectively. Subjects overestimated the 90 ° position across all conditions, whereas the accuracy of the 135 ° estimate varied. Angle estimates were most accurate during isokinetic FLX for 90 °(mean error +9.8 °) and isokinetic EXT for 135 ° (mean error +0.7°). No differences occurred between passive vs. active isokinetic EXT or FLX. Estimates of each joint angle during isokinetic EXT were less than isotonic EXT, but greater than isokinetic FLX (P<0.05). During spaceflight, joint angle estimates were lower during isokinetic FLX and EXT for 90 °(P<0.05) and 135 ° (P≤0.10) compared to preflight. Spaceflight also decreased angle estimates during isotonic FLX and EXT (P<0.05). Elbow angle estimates had returned to preflight values one day after return to 1G. These data demonstrate that elbow joint angle estimation was: 1) decreased during spaceflight, particularly for isotonic conditions 2) rapidly restored to preflight values upon return to 1G; and 3) not changed by low level agonist muscle exertion during isokinetic movements. These data indicate that the proprioception of elbow joint position is altered by microgravity, but rapidly readapts to preflight control values after return to 1G.