Sharp Changes in Muscle Tone in Humans Under Simulated Microgravity

Abstract

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.

Dry immersion induced acute low back pain and its relationship with trunk myofascial viscoelastic changes

“…DI via resonance vibrography has been demonstrated to induce a rapid change in myofascial tissue properties, including a bilateral decrease in back extensor tone (m. longissimus dorsi in the projection of L2-L3) (Rukavishnikov et al, 2017). Furthermore, a rapid bilateral drop in m. erector spinae (in T9-T8, T12-L1, and L3-L4 cord projection) and trapezius muscle tone were recently observed during up to 2 h of DI (Amirova et al, 2021). However, whether such changes persist, and are correlated with LBP is unclear.…”

Measuring Mechanical Properties of Spastic Muscles After Stroke. Does Muscle Position During Assessment Really Matter?

“…Myotonometry is a valid and easy-to-use approach to objectively quantify muscle mechanical properties in people after stroke. 4,6 However, its high environmental sensitivity 4 and the large withinand between-participants variability 19 together with assessmentrelated aspects, such as muscle position and operator's experience, 4,20 stress the importance of agreeing on a standardized evaluation protocol.…”

Psychophysiological Indicators of Postural Control. Contribution of the Russian Scientific School. Part I

“…These studies have contributed considerably to the study of support afferentation in physiology, from cellular responses of postural muscle to psychological characteristics of human behavior. It has been established that removing leg support inactivates the pool of slow motor units, which leads to selective inactivation and subsequent atony [ 11 ] and the atrophy of muscle fibers expressing the slow isoform myosin heavy chain (which comprises most of the soleus muscle fibers). The fibers that have lost a significant portion of cytoskeleton molecules are incapable of effective actomyosin motor mobilization, which leads to low calcium sensitivity [ 92 ] and a narrow range of maximum tension [ 93 ].…”

“…At the same time, a unique role is given to support afferentation (feeling underfoot support). The weakening of feedback from baroreceptors of the foot can cause numerous disorders, beginning from impaired biosynthesis of the structural proteins of muscle tissue [ 10 ] to the pathology of the entire musculoskeletal system [ 11 , 12 ], the cardiovascular respiratory [ 9 ], endocrine [ 13 ] and other vegetative systems [ 14 ]. For example, the study of the organization of the sensorimotor system of postural control resulted in the appearance of new terms: “gravitational mechanisms” and “support afferentation” [ 8 ], as well as the development of the concepts of afferent control of locomotion [ 8 , 12 ], biomechanical studies of the system of internal representation in locomotion control by Yu.A.…”