Bed Rest, Exercise Countermeasure and Reconditioning Effects on the Human Resting Muscle Tone System

Abstract

The human resting muscle tone (HRMT) system provides structural and functional support to skeletal muscle and associated myofascial structures (tendons, fascia) in normal life. Little information is available on changes to the HRMT in bed rest. A set of dynamic oscillation mechanosignals ([Hz], [N/m], log decrement, [ms]) collected and computed by a hand-held digital palpation device (MyotonPRO) were used to study changes in tone and in key biomechanical and viscoelastic properties in global and postural skeletal muscle tendons and fascia from a non-exercise control (CTR) and an exercise (JUMP) group performing reactive jumps on a customized sledge system during a 60 days head-down tilt bed rest (RSL Study 2015–2016). A set of baseline and differential natural oscillation signal patterns were identified as key determinants in resting muscle and myofascial structures from back, thigh, calf, patellar and Achilles tendon, and plantar fascia. The greatest changes were found in thigh and calf muscle and tendon, with little change in the shoulder muscles. Functional tests (one leg jumps, electromyography) showed only trends in relevant leg muscle groups. Increased anti-Collagen-I immunoreactivity found in CTR soleus biopsy cryosections was absent from JUMP. Results allow for a muscle health status definition after chronic disuse in bed rest without and with countermeasure, and following reconditioning. Findings improve our understanding of structural and functional responses of the HRMT to disuse and exercise, may help to guide treatment in various clinical settings (e.g., muscle tone disorders, neuro-rehabilitation), and promote monitoring of muscle health and training status in personalized sport and space medicine.

Reactive Jumps Preserve Skeletal Muscle Structure, Phenotype, and Myofiber Oxidative Capacity in Bed Rest

“…Accumulating evidence suggests that ECM not only matters in terms of mechanics but also takes part in determining the skeletal muscle's phenotype and probably also takes some part in strength output. As previously reported from the same study, rectus femoris muscle (medial part of quadriceps femoris) resting muscle stiffness (viscoelasticity) determined by the non-invasive Myoton technology increased in JUMP during RSL long-term bed rest and returned to baseline (pre bed rest) faster than observed in CTRL following recovery thereafter (Schoenrock et al, 2018). At bed rest end, for example, rectus femoris in CTRL showed a reduction in resonance frequency and material stiffness, which can jointly be thought to represent passive muscle "tone" (Schoenrock et al, 2018).…”

“…As previously reported from the same study, rectus femoris muscle (medial part of quadriceps femoris) resting muscle stiffness (viscoelasticity) determined by the non-invasive Myoton technology increased in JUMP during RSL long-term bed rest and returned to baseline (pre bed rest) faster than observed in CTRL following recovery thereafter (Schoenrock et al, 2018). At bed rest end, for example, rectus femoris in CTRL showed a reduction in resonance frequency and material stiffness, which can jointly be thought to represent passive muscle "tone" (Schoenrock et al, 2018). Possible links may also exist between structural and functional myofiber properties, tissue viscoelasticity, capillarization, and microvascular network adaptation in disuse without and with exercise that need further investigation.…”

“…To investigate this, we analyzed changes in myofiber CSA and the induction/prevention of myofiber type shift (slow-to-fast) in VL and SOL biopsy samples from the RSL Study using high-resolution confocal microscopy, quantitative structural capillarization parameters, combined with fiber maximal oxygen consumption (VO 2max ) estimations by optical density (OD 660nm )-based semiquantitative mitochondrial succinate dehydrogenase (SDH) histochemistry performed on freshly cut tissue cryosections. Together with previous RSL-Study reports (Kramer et al, 2017b(Kramer et al, , 2018Koschate et al, 2018;Maggioni et al, 2018;Schoenrock et al, 2018), the present investigations using muscle biopsy samples from two different functional leg muscles (prime knee extensor and deep plantar flexor) provide evidence that high-impact reactive jumps maintained myofiber size and phenotype with a trend only to also preserve oxidative capacity analyzed in the prime knee extensor VL in HDT bed rest. Nevertheless, high-impact interval training could be a short and effective exercise surrogate for multimodal/multisystem training protocols on Earth and for crew members in long-duration space missions.…”

Skeletal Muscle Extracellular Matrix – What Do We Know About Its Composition, Regulation, and Physiological Roles? A Narrative Review

“…In non-exercising humans, immunohistochemical staining suggested no changes in the density of the collagen I network after 60 days of bed rest. In subjects performing a countermeasure exercise protocol consisting of reactive jumps on a sledge system, by contrast, collagen I immunoreactivity was reduced as compared to baseline levels (Schoenrock et al, 2018).…”

The march in place activity – a view from the local concentration of red blood cells (CRBC) in the human foot dorsum

“…However, when comparing Phase 3 (recovery) with baseline (Phase 1), we found that muscle activity is still significantly elevated (p=0.010), likely due to the maintenance of a higher physiologic postural tone. The gastrocnemius muscle is considered one of the most important muscles in functional control and stabilization of the standing position with reference to a set of natural base and differential oscillation signal patterns, identified as key determinants in muscle rest [23]. We found two studies that address muscle stiffness and tone after exercise, and in one study, differences were recorded iwithin 5 minutes after the end of exercise [24].…”