Hypogravity reduces trunk admittance and lumbar muscle activation in response to external perturbations

Enrico de Martino, Sauro E. Salomoni, Andrew Winnard, Kristofor McCarty, Kirsty Lindsay, Sherveen Riazati, Tobias Weber, Jonathan Scott, David A. Green, Julie Hides, Dorothée Debuse, Paul W. Hodges, Jaap H. van Dieën, Nick Caplan*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

8 Citations (Scopus)


Reduced paraspinal muscle size and flattening of spinal curvatures have been documented after spaceflight. Assessment of trunk adaptations to hypogravity can contribute to development of specific countermeasures. In this study, parabolic flights were used to investigate spinal curvature and muscle responses to hypogravity. Data from five trials at 0.25 g, 0.50 g, and 0.75 g were recorded from six participants positioned in a kneeling-seated position. During the first two trials, participants maintained a normal, upright posture. In the last three trials, small-amplitude perturbations were delivered in the anterior direction at the T10 level. Spinal curvature was estimated with motion capture cameras. Trunk displacement and contact force between the actuator and participant were recorded. Muscle activity responses were collected by intramuscular electromyography (iEMG) of the deep and superficial lumbar multifidus, iliocostalis lumborum, longissimus thoracis, quadratus lumborum, transversus abdominis, obliquus internus, and obliquus externus muscles. The root mean square iEMG and the average spinal angles were calculated. Trunk admittance and muscle responses to perturbations were calculated as closed-loop frequency-response functions. Compared with 0.75 g, 0.25 g resulted in lower activation of the longissimus thoracis (P = 0.002); lower responses of the superficial multifidus at low frequencies (P = 0.043); lower responses of the superficial multifidus (P = 0.029) and iliocostalis lumborum (P = 0.043); lower trunk admittance (P = 0.037) at intermediate frequencies; and stronger responses of the transversus abdominis at higher frequencies (P = 0.032). These findings indicate that exposure to hypogravity reduces trunk admittance, partially compensated by weaker stabilizing contributions of the paraspinal muscles and coinciding with an apparent increase of deep abdominal muscle activity.

Original languageEnglish
JournalJournal of Applied Physiology
Issue number4
Pages (from-to)1044-1055
Number of pages12
Publication statusPublished - Apr 2020

Bibliographical note

Funding Information:
Funding for this study was received from the UK Space Agency and European Space Agency. P. W. H. was supported by a Fellowship (APP1102905) from the National Health and Medical Research Council (NHMRC) of Australia. S. E. S. was funded by a grant (APP1091302) from the NHMRC.

Publisher Copyright:
Licensed under Creative Commons Attribution CC-BY 4.0: © the American Physiological Society.


  • Intramuscular electromyography
  • Low gravity
  • Lumbar spine
  • Parabolic flight
  • Trunk stabilization


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