Motor performance and motor learning in sustained +3 Gz acceleration.

Introduction: Previous studies have shown that increased head-to-foot acceleration (+Gz) like that experienced in maneuvering aircraft impairs motor performance. However, there are few studies of motor performance providing detailed descriptions of specific deficits (e.g., mechanical function, timing, or loss of accuracy), and almost none investigating motor learning processes. Therefore, the present study evaluated whether these parameters may explain tracking deficits during +Gz, and whether +Gz also affects motor learning.

Methods: To investigate motor performance, a Test Group (N = 10) manually tracked a sinusoidal moving target either in normal Earth gravity or during steady-state acceleration (+3 Gz). Cursor feedback was then left-right reversed, and subjects had to adapt their performance to this disturbance while remaining in the same acceleration environment. A Control Group (N = 10) performed the same paradigm in 1 G; a Weight Group (N = 12) also remained at 1 G with additional arm weighting to simulate the +3-Gz load.

Results: Tracking performance in +3 Gz was impaired by about 50% compared to 1-G values. The deficit was not entirely due to the mechanical effect of +3 Gz, since performance in the Weight Group decreased by only about 25%. Moreover, tracking accuracy but not tracking timing was impaired at +3 Gz. Left-right switching resulted in typical motor learning in all subjects. Exposure to +3 Gz had no influence on motor learning.

Discussion: Deficits in tracking performance are probably not due to mechanical impairment or timing deficits, but rather reflect effects on accuracy due to vestibulo-spinal influences or the stressful environment at +3 Gz However, these effects do not impair motor learning.