INTRODUCTION: During centrifuge-simulated suborbital spaceplane flights, launch and re-entry frequently cause visual symptoms, and G-induced loss of consciousness can occur. G-related effects may be more prominent during re-entry from microgravity on actual flights. A modified anti-G maneuver that does not involve a breath strain and is suitable for members of the public may be effective against these effects.

METHODS: Recruited were 13 healthy subjects (age range 34–82 yr) who had experienced visual symptoms during centrifuge-simulated suborbital centrifuge profiles as part of a previous study. Onset and duration of greyout were recorded during an acceleration profile simulating spaceplane launch and re-entry in an upright seated position. The profile was undertaken twice: once in a relaxed state and once while undertaking anticipatory muscle tensing consisting of pre-tensing the leg and abdominal muscles (i.e., the muscle tensing component of a standard aircrew anti-G straining maneuver).

RESULTS: Muscle tensing was well tolerated and prevented 100% of greyout on launch and 54% of greyout on re-entry, as well as delaying the onset of greyout when it did occur on re-entry. Combined with the previous study’s data, this indicates an overall population incidence of greyout of ∼70% on launch, falling to zero with muscle tensing, and ∼80% on re-entry, falling to ∼37% with muscle tensing.

DISCUSSION: Anticipatory pre-tensing of leg and abdominal muscles prevented greyout completely during the launch phase and partially during re-entry, and should be considered as part of routine suborbital spaceplane operations. Studies providing relevant data from actual flights are required.

Pollock RD, Britton JK, Green NDC, Hendriksen D, Hodkinson PD, Anderton RA, Smith TG. Prevention of G-induced effects on vision and consciousness during simulated suborbital spaceflight. Aerosp Med Hum Perform. 2024; 95(12):897–901.