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May 2021

Sharp Changes in Muscle Tone in Humans Under Simulated Microgravity

Authors: Liubov E. Amirova 1, Anastasija Plehuna 2, Ilya V. Rukavishnikov 3, Alina A. Saveko 1, Aleko Peipsi 4 and Elena S. Tomilovskaya 1

Author information:

  1. Laboratory of Gravitational Physiology of the Sensorimotor System, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia
  2. King’s College London, Centre of Human & Applied Physiological Sciences, London, United Kingdom
  3. Department of Medical Support for Spaceflight, Institute of Biomedical Problem of Russian Academy of Science, Moscow, Russia
  4. Myoton AS, Tallinn, Estonia

Journal: Frontiers in Physiology - May 2021, Volume 12, Article 661922 (DOI: 10.3389/fphys.2021.661922)

A decrease in muscle tone induced by space flight requires a standardized assessment of changes to control the state of the neuromuscular system. This study is a step toward the development of a unified protocol, aimed at determining the initial effect of the presence or withdrawal of support on muscle tone, the effects of a 2-h supportlessness in Dry Immersion (DI) experiments, and the changes in muscle tone depending on the site of measurement. To perform measurements of changes in muscle tone, we used a MyotonPRO device. The list of muscles that we assessed includes: trunk – mm. deltoideus posterior, trapezius, erector spinae; leg – mm. biceps femoris, rectus femoris, tibialis anterior, soleus, gastrocnemius; foot – m. flexor digitorum brevis, tendo Achillis, aponeurosis plantaris. The study involved 12 healthy volunteers (6 men, 6 women) without musculoskeletal disorders and aged 32.8 ± 1.6 years. At the start of DI, there was a significant decrease in muscle tone of the following muscles: mm. tibialis anterior (−10.9%), soleus (−9.6%), erector spinae (−14.4%), and the tendo Achillis (−15.3%). The decrease continued to intensify over the next 2 h. In contrast, the gastrocnemius muscle demonstrated an increase in muscle tone (+7.5%) 2 h after the start of DI compared to the immediate in-bath baseline. Muscle tone values were found to be site-dependent and varied in different projections of mm. erector spinae and soleus. In previous experiments, we observed a high sensitivity of the myotonometry technique, which was confirmed in this study. To make it possible to compare data from different studies, a standardized protocol for measuring muscle tone for general use in gravitational physiology needs to be developed.

 

Keywords: muscle tone, atony, MyotonPRO, Dry Immersion, microgravity, space flight

A decrease in postural muscle tone occurred immediately after the start of immersion and intensified after the first 2 h of immersion. The degree of muscle change depended on the experimental condition that was chosen as the reference value (on-couch or in-bath). Moreover, the measurement site was critical for assessing the degree of change in muscle tone within a single muscle.

To make it possible to compare data from different studies, a standardized protocol for measuring muscle tone for general use in the field of gravitational physiology needs to be developed.

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