Abstract: Any deficits in neuromuscular function during space missions can compromise overall performance, including reduced exercise effectiveness in flight and impaired balance and coordination post-landing [1, 2]. Understanding spinal reflex alterations during microgravity exposure is a crucial step toward establishing predictors of functional performance and biomarkers of sensorimotor health. A novel method, transcutaneous spinal cord stimulation (TSS), offers crucial insights into assessing spinal excitability across multiple spinal segments [3]. The objective of this study was to investigate spinal adaptations during the ground-based microgravity model, Dry Immersion (DI), with a specific focus on changes in reflex activity within multisegmental spinal networks. We hypothesized that spinal adaptations during DI would manifest as increased reflex activity in leg flexors, accompanied by a corresponding decrease in reflex activity in leg extensors. Fourteen healthy females participated in a 5-day DI. TSS of varying intensities was applied over the T11-T12 intervertebral space using surface adhesive electrodes. Electromyography (EMG) responses were recorded bilaterally from the vastus lateralis (VL), medial hamstring (MH), tibialis anterior (TA), and soleus (SOL) muscles. Tests were conducted twice before DI, then at 8 hours, 3 days, and 5 days after DI onset, as well as 2 days post-DI. TSS tests were well-tolerated by all participants. A peak decline of approximately 10% in motor threshold values was observed in both flexors and extensors by day 3 of DI (p < 0.05). Maximum response amplitudes decreased in the VL and SOL muscles. Neurophysiological profiling of the propriospinal system using multisegmental spinal reflexes has proven to be safe, well-tolerated, and sensitive to spinal motoneuron-level changes during the ground-based microgravity model Dry Immersion. When combined with other approaches that assess different levels of the neuroaxis, this method can provide valuable insights into changes in vestibulospinal and corticospinal interactions, as well as neuromuscular control, resulting from factors such as somatosensory deafferentation and muscle disuse during microgravity.

Cite: Sayenko D.G. , Bychkova A.D. , Kitov V.V. , Abu Shelly N.M.A. , Tomilovskaya E.S. , Shigueva T.A.
NEUROPHYSIOLOGICAL PROFILING OF THE PROPRIOSPINAL SYSTEM USING MULTISEGMENTAL SPINAL REFLEXES IN THE GROUND-BASED MICROGRAVITY MODEL DRY IMMERSION
NASA Human Research Program Investigators 28-31 Jan 2025