Alterations in muscle contractile properties, structure, and function during 10-d bed rest, postrecovery, and after COVID-19 lockdownŠimunič, Boštjan (Avtor) Sarto, Fabio (Avtor) Franchi, Martino V. (Avtor) Monti, Elena (Avtor) Pišot, Rado (Avtor) Narici, Marco Vincenzo (Avtor) atrophydisuseskeletal muscletensiomyographyultrasoundWe aimed to identify early tensiomyography alterations in six muscles during a 10-d bed rest (BR10), followed by a 30-d recovery period (R+30), and to compare these changes with those observed after the 50-d COVID-19 lockdown in 10 healthy males (22.9 ± 5.0 yr). Methods: Tensiomyography and muscle thickness (assessed by ultrasound imaging) were assessed at baseline, during bed rest, at BR10, R+30, and after the COVID-19 lockdown. Additional assessments included vertical jump performance (force plate), body composition (bioimpedance), physical activity (Global Physical Activity Questionnaire), and lower back pain (VAS). Results: By BR10, participants experienced a 1.9% body mass loss, a 3.8% increase in fat mass, and a 2.4% reduction in muscle mass. Although anthropometric parameters returned to baseline by R+30, fat mass increased again by 3.9% postlockdown. Jump height declined by 10.1% at BR10, returned to baseline at R+30, and remained stable thereafter. Muscle thickness decreased by 7.0% in the vastus lateralis at BR10 and by 10.1% postlockdown. Tensiomyographic amplitude increased in five leg muscles before BR10, recovered at R+30 and increased again after postlockdown, whereas a reduction was observed in the erector spinae within the first 48 h, coinciding with reported lower back pain. In the erector spinae, both delay and contraction time decreased during BR10 and postlockdown, whereas contraction time of the biceps femoris increased before BR10 and remained elevated postlockdown. Conclusions: The observed post COVID-19 lockdown alterations in tensiomyographic parameters followed the same trend as those induced by bed rest, albeit with smaller magnitude. These findings support the utility of TMG as a sensitive and noninvasive method for monitoring muscle responses across different disuse paradigms. 20262026-08-21 10:09:39Neznano31972UDK: 796.01:612ISSN pri članku: 1530-0315DOI: 10.1249/MSS.0000000000003986COBISS_ID: 288421891slCopyright © 2026 The Author(s)