New publication: NIRSBOX tissue oximetry captures the metabolic impact of bed rest on skeletal muscle.
A new paper in Experimental Physiology reports how prolonged bed rest alters skeletal muscle oxygen use in both young and older adults, using time-domain tissue oximetry with the PIONIRS NIRSBOX. In the study, the device was applied over the vastus medialis to track muscle oxygenation during transient ischaemia and to estimate resting muscle O₂ uptake (V̇O₂m) from the early decline in muscle oxygen saturation. The TD-NIRS approach also provided absolute tissue parameters, including SmO₂ (Muscle Tissue Oxygenation) and total hemoglobine: THb [oxy + deoxy (Hb + Mb)], adding quantitative depth to the physiological analysis.
The main NIRSBOX-based finding was clear: resting muscle O₂ uptake fell markedly after bed rest. In young participants, resting V̇O₂m decreased by 45% after 21 days of bed rest, while in elderly participants it decreased by 29% after 10 days. In the young group, almost the entire reduction had already occurred by day 10, indicating that these metabolic adaptations emerge early during disuse.
Beyond the V̇O₂m result, the tissue oximetry measurements added important detail. Resting SmO₂ remained relatively stable across conditions, while the THb[oxy + deoxy(Hb + Mb)] signal decreased in the young group during bed rest, from 148.5 ± 28.4 μM at baseline to 123.2 ± 21.7 μM at day 10 and 122.1 ± 21.8 μM at day 21. In the elderly group, baseline total haemoglobin + myoglobin values were lower overall and did not significantly change with bed rest. This is a valuable example of how TD-NIRS can move beyond relative trends and provide quantitative information on tissue oxygenation and local haemodynamic-muscular changes.
The paper links these NIRS findings with broader physiology. The drop in resting muscle O₂ uptake was accompanied by a decrease in whole-body resting energy expenditure, suggesting a disuse-related recalibration of oxidative metabolism. In elderly subjects, the reduction in V̇O₂m was consistent with a parallel drop in citrate synthase activity, whereas in young subjects V̇O₂m remained lower even after normalization for citrate synthase, pointing to additional qualitative metabolic adaptations beyond mitochondrial content alone.
The spaceflight relevance is especially timely. The authors note that a lower resting energy demand could, in principle, reduce consumable needs during long missions, while also stressing that inactivity itself has important physiological costs and cannot replace exercise countermeasures. That perspective resonates strongly as Artemis II, NASA’s first crewed Artemis mission, carries astronauts on a roughly 10-day lunar flyby and helps define the next phase of deep-space human exploration. NASA also reports that the Artemis II crew surpassed the previous record for the farthest human spaceflight during the mission. Studies like this one help clarify how muscle disuse reshapes oxygen use and metabolism, and why understanding these mechanisms matters for protecting astronaut health during deep-space travel and recovery after return.
We would like to express our sincere thanks to the authors of this work, to the participants who made the study possible, and to all those involved in the experiments, analysis, and interpretation. It is a true honour for PIONIRS to be part of a study involving such respected researchers in exercise and muscle physiology. We also warmly acknowledge the medical, technical, and nursing staff in Izola and Koper whose work supported the bed rest campaign. We are proud to see NIRSBOX included in this rigorous collaborative effort and grateful to be part of research that connects quantitative tissue oximetry with questions of real relevance for physiology, rehabilitation.
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Baldassarre, G., Porcelli, S., Zuccarelli, L., Brocca, L., Arboit, N., Gobbo, L., Lacerenza, M., Marciano, A., Motto, C., Sanguin, G., Gasparini, M., Šimunič, B., Pišot, R., Narici, M., & Grassi, B. (2026). Bed rest decreases resting skeletal muscle O2 uptake and resting energy expenditure in young and elderly subjects. Experimental Physiology, 1–14. https://doi.org/10.1113/EP092709
