Mental - and temporal - demand NASA - task load Index scores correlate with decreases in irisin serum levels in healthy individuals subjected to 10-day bed restPignataro, Patrizia (Avtor) Marušič, Uroš (Avtor) Zerlotin, Roberta (Avtor) Oranger, Angela (Avtor) Dicarlo, Manuela (Avtor) Suriano, Clelia (Avtor) Taurisano, Paolo (Avtor) Pišot, Rado (Avtor) Šimunič, Boštjan (Avtor) Narici, Marco Vincenzo (Avtor) bed restmicrogravityirisincognitive performanceNASA-TLX indeksBackground Bed rest (BR) is a widely used analogue of space flight that aims to replicate microgravity conditions, such as immobilization and a lack of sensorimotor stimuli. In a previous BR study, we evaluated the changes in irisin serum levels, a myokine produced mainly by skeletal muscle that exerts pleiotropic effects on several organs, including the brain. Objective Here, we evaluated whether the decline in circulating irisin concentrations during 10 days of horizontal BR correlated with the National Aeronautics and Space Administration Task Load Index (NASA-TLX). Methods NASA-TLX was obtained from young healthy participants at the end of the BR protocol. It is a self-report measure of task load that includes six subscales: mental demand, physical demand, temporal demand, performance, effort, and frustration. Each subscale score was correlated with the decline in serum irisin levels measured while participants were supine. Irisin decline was calculated as the difference between levels on the first day of BR (BR0) and the last day (BR9). Results Our results show a significant positive correlation between irisin decline and both mental demand and temporal demand, whereas correlations with the remaining subscales showed a positive association with irisin decline but did not reach statistical significance. Conclusion These findings suggest that reduced irisin levels are associated with increased perceived mental demand and time pressure (temporal demand) during BR. Because temporal demand can exacerbate high mental activity in a state of cognitive overload, maintaining higher circulating irisin levels could represent an effective countermeasure to improve the cognitive performance of participants during future BR studies and may help astronauts manage mental and temporal pressure during space missions.20262026-04-09 12:59:33Neznano28851sl© 2026 by the Author(s).