Responses of Muscle Volume, Strength, and Motor Unit Properties to Bed Rest and Retraining in Young Males and Females

Sarto, F.; Kalc, M.; Caputo, O.; Pus, K.; Magris, R.; Martino, G.; Brusco, C. M.; Franchi, M. V.; De Vito, G.; Ferranti, F.; Simunic, B.; Pisot, R.; Narici, M. V.

doi:10.64898/2026.11.04.764387

bioRxiv · 10.64898/2026.11.04.764387

Responses of Muscle Volume, Strength, and Motor Unit Properties to Bed Rest and Retraining in Young Males and Females

Sarto, F.·Kalc, M.·Caputo, O.·Pus, K.·Magris, R.·Martino, G.·Brusco, C. M.·Franchi, M. V.·De Vito, G.·Ferranti, F.·Simunic, B.·Pisot, R.·Narici, M. V.

View original source ↗Export metadata ↓

Abstract

Sex differences in motor unit (MU) properties to simulated microgravity are unknown. Young males and females completed a 21-day head-down bed rest followed by a 21-day retraining. Bed rest reduced knee extensor strength and volume without sex differences. MU firing rate decreased in both groups, more in females, alongside increased serum C-terminal agrin fragment. After retraining, these measures returned to baseline, whereas strength only partially recovered, remaining below baseline.

Explore related subjects

physiology Preprint

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Sarto, F., Kalc, M., Caputo, O., Pus, K., Magris, R., Martino, G., Brusco, C. M., Franchi, M. V., De Vito, G., Ferranti, F., Simunic, B., Pisot, R., Narici, M. V.. 2026-11-06. Responses of Muscle Volume, Strength, and Motor Unit Properties to Bed Rest and Retraining in Young Males and Females. https://doi.org/10.64898/2026.11.04.764387

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Residual Hearing Loss After Chronic Cochlear Implantation in Guinea Pigs is Primarily Conductive

It is desirous to preserve residual low-frequency hearing in cochlear implant recipients, as dual stimulation using electrical and acoustic signals results in superior speech-in-noise processing and musicality. However, cochlear implant recipients commonly lose their residual acoustic hearing gradually following surgical placement of the array. The governing mechanism is not understood and is likely due to multiple factors including surgical trauma, inflammation, and the foreign body induced immune response to the array, including formation of intracochlear fibrosis. Normal mechanical function of the cochlea is expected to underpin residual hearing but has not been directly studied. This function includes efficient transmission of sound to the cochlea via the middle ear, sound propagation via the basilar membrane travelling wave, mechanical tuning characteristics, and the non-linear cochlear amplification of responses to low-frequency stimulation. Here, we examined these features in cochleae and middle ears of unimplanted, acutely and chronically implanted guinea pigs using our minimally invasive preparation and optical coherence tomography vibrometry. We observed that mechanical tuning and amplification is not significantly altered by either acute or chronic implant. However, the response threshold was raised and proportional to middle ear responses. Additionally, the organ of Corti phase, and its sound intensity dependent changes, are unaltered by CI. Finally, a cluster analysis revealed sensitivity loss in chronically implanted animals is caused by middle ear dysfunction. Hence, in the guinea pig model, the dominant etiology of residual hearing loss is conductive. More research is required to establish whether residual hearing loss in humans similarly shares conductive elements.

physiology↗

bioRxiv2026

Satellite cell glucocorticoid receptor restrains myogenic commitment without mediating the effects of therapeutic glucocorticoids on muscle repair

Glucocorticoids (GCs) exert profound effects on skeletal muscle, but the contribution of satellite cell (SatC) glucocorticoid receptor (GR) signaling to muscle regeneration remains poorly understood. Here, we investigated the role of GR in SatC homeostasis and assessed whether SatC GR mediates the effects of therapeutic GCs on muscle repair. Conditional deletion of GR in SatC reduced the number of PAX7-positive cells during regeneration in young mice, but did not substantially impair muscle repair in either young or aged animals. Transcriptomic and chromatin profiling revealed that GR occupies genes involved in stem cell fate and developmental signaling, with extensive GR binding already established in quiescent SatC. GR-deficient quiescent SatC showed reduced expression of Yap1, Runx1 and Foxo1, together with increased Myog expression. Similarly, GR silencing in human myoblasts induced early myogenic differentiation markers without affecting proliferation, supporting a conserved role for GR in restraining myogenic commitment. We next examined the effects of two therapeutic GCs on muscle regeneration. Chronic prednisone treatment altered the transcriptional landscape of regenerating muscle in an age-dependent manner, without substantially affecting histological repair. In contrast, dexamethasone administration during the early inflammatory phase delayed regeneration, with persistent necrosis and increased collagen deposition. These effects were comparable in control and SatC-specific GR-deficient mice, indicating that they do not require GR in SatC. Together, these findings identify GR as a regulator of the quiescent, undifferentiated state of SatC, while showing that the effects of therapeutic GCs on muscle repair are largely independent of SatC GR. They further highlight the importance of treatment regimen and physiological context in determining the effects of GCs on skeletal muscle regeneration.

physiology↗

bioRxiv2026

Functional Assessment and Extended Culture of Human Pediatric Cardiac Tissue Slices for Preclinical Testing

Background: Living human myocardial slices preserve native tissue architecture, but their application to pediatric cardiac physiology or prolonged functional testing remains limited. We adapted a passive culture method for small surgical myocardial specimens obtained from patients with congenital heart disease (CHD). Methods: Atrial and ventricular specimens were obtained from 41 cardiac surgery patients (7.7{+/-}11.1 years; 1 day-49 years). Myocardial tissue was sectioned into slices and studied acutely, or maintained under free floating, rocking cell culture conditions without electrical or mechanical stimulation. Calcium transients were recorded in response to external pacing (0.2-2 Hz) at baseline, and after isoproterenol or norepinephrine exposure. Selected preparations underwent viability, histological, and gene expression analyses. Results: Pacing evoked calcium transients were recorded from all four cardiac chambers, exhibiting expected frequency-dependent shortening. Mean interslice and intraslice coefficients of variation were 11.1% and 7.6%. Viability was 85.8 {+/-} 5.6% post-slicing and 78.8 {+/-} 5.0% after 3-5 hours. Calcium transients remained detectable through 178 days in atrial and 119 days in ventricular slices. Calcium transient durations were relatively stable during extended culture. Beta-adrenergic agonists shortened calcium transient durations (isoproterenol: 32% atrial, 25% ventricular at 0.3 Hz); responses to isoproterenol persisted to approximately 120 days in selected atrial slices and 60 days in ventricular slices. Selected histological features were preserved, although some extracellular matrix and apoptosis related transcripts changed. Conclusions: Small surgical specimens support repeated physiological measurements and pharmacological testing during extended passive culture, providing a platform for human developmental and disease-specific cardiac research.

physiology↗