Effect of Three Weeks of Strict Head‑Down Tilt Bed Rest on Human Muscle Function and Architecture.
In: Human Physiology, Jg. 49 (2023-12-01), Heft 6, S. 589-604
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Zugriff:
The purpose of this study was, first, to quantitatively describe the relationship between joint angles and muscle architecture (length, fiber angle) and thickness of the medial gastrocnemius muscle (MGM) in young men in vivo under passive (relaxed) and active (contracting) states and, secondly, compare changes in the above characteristics of muscle architecture that occur during the transition from a resting state to a given isometric intensity during plantar flexion under conditions of 21-day anti-orthostatic hypokinensia (AOH) caused by relatively strict head-down tilt bed rest (HDBR), involving six men. MGM scanning was performed using ultrasound (US) at 30% of the distance between the popliteal crease and the center of the lateral malleolus at rest at ankle angles of –15° (dorsiflexion), 0° (neutral position), +15°, and +30° (plantar flexion). Additional USs were performed during maximum voluntary contraction (MVC) and at forces of 80, 60, 40, and 20% MVC with the ankle in neutral position. In each position, longitudinal ultrasound images of the MGM were obtained in relaxed (passive) and active states with determination of the length (L F ) and the angle of inclination of the fibers (Θ F ) relative to the aponeurosis. After AOH, MVC increased by 4.1%. Before AOH, with an increase in the ankle joint angle, MGM from 15 to + 30° (Θ F ) increased from 23 to 27 (19.4%, p < 0.05) at rest and from 23 to 53 (130%; p < 0.01) during MVC, and L F decreased from 32 to 27 mm (15.6%, p < 0.05) at rest and from 36 to 22 mm (39%; p < 0.05) during MVC. MGM thickness did not differ significantly between rest and MVC. After AOH, (Θ F ) MGM during the development of MVC was increased by 22–47 (113.6%, p < 0.01), and L F was decreased by 31–21 mm (32.2%, p < 0.01) compared to rest. During the performance of graded isometric force from rest to 100%, MVC (Θ F ) gradually increased from 32 to 47 (44.8%, p < 0.01), and L F decreased from 27 to 23 mm (14.8%, p < 0.01). MGM thickness remained constant during graded isometric force up to 80% of MVC with the ankle in neutral position. Various L F and (Θ F ) and their changes after AOH can be limiting factors in the generation of muscle contractile functions. The results of the study show that both the inclination and length of the MGM fibers alter both in response to changes in ankle joint angle at rest and during isometric contractions at intensities up to 100% MVC. Changes in muscle structure after 21-day unloading of the muscular apparatus under AOH conditions during contraction compared to rest, assessed by changes in muscle architecture, can be used in assessing the mechanical production of muscles. [ABSTRACT FROM AUTHOR]
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Titel: |
Effect of Three Weeks of Strict Head‑Down Tilt Bed Rest on Human Muscle Function and Architecture.
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Autor/in / Beteiligte Person: | Koryak, Yu. A. ; Prochiy, R. R. ; Knutova, N. S. |
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Zeitschrift: | Human Physiology, Jg. 49 (2023-12-01), Heft 6, S. 589-604 |
Veröffentlichung: | 2023 |
Medientyp: | academicJournal |
ISSN: | 0362-1197 (print) |
DOI: | 10.1134/S0362119723700445 |
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