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Povzetek: Chronic bed rest (BR) serves as a model for studying the effects of prolongedimmobility on physiological and neuromotor functions, particularly postural control. ProlongedBR leads to significant deconditioning of postural balance control, characterized by increasedsway path lengths, sway velocity and fall risk, independent of muscle strength. These changes arelinked to neural adaptations at spinal and supraspinal levels, including structural and functionalbrain changes, such as alterations in grey and white matter, increased cerebellar activation,reduced spinal excitability and increased latencies within reflex circuitries. Additionally, BRdisrupts sensory integration from proprioceptive, visual and vestibular systems, impairing post-ural stability. Visual reliance remains stable during BR, though decreased visual acuity andcontrast sensitivity are noted. Moreover, BR-induced shifts in cerebrospinal fluid contribute toaltered brain activity, impacting sensorimotor function. Vestibular system adaptations, includingchanges in vestibulospinal reflexes, further exacerbate balance impairments. Understanding thesemechanisms is crucial for developing interventions to mitigate the adverse effects of BR onpostural control and prevent prolonged recovery times or increased risk of injury. This reviewhighlights the need for further research into the neural underpinnings of BR-induced posturalinstability, with a focus on sensory integration and neuroplasticity
Ključne besede: atrophy, balance, disuse, immobilization, muscle
Objavljeno v DiRROS: 18.04.2025; Ogledov: 541; Prenosov: 327
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Povzetek: We examined activation patterns of the gastrocnemius medialis (GM), gastrocnemius lateralis (GL), soleus (SO), and tibialis anterior (TA) muscles in eight older (58.4 ± 3.3 years) and seven young (23.1 ± 2.9 years) participants, before and after 14 days of horizontal bed rest. Visual feedback on the exerted muscle torque was provided to the participants. The discharge patterns of individual motor units (MUs) were studied in three repetitions of isometric plantar flexion at 30 and 60% of Maximum Voluntary Contraction (MVC), before, and 1 day after the 14-day bed rest, respectively. In the GL and GM muscles, the older participants demonstrated higher MU discharge rates than the young, regardless of the contraction level, both before and after the bed rest. In the TA and SO muscles, the differences between the older and young participants were less consistent. Detailed analysis revealed person-specific changes in the MU discharge rates after the bed rest. To quantify the coactivation patterns we calculated the correlation coefficients between the cumulative spike trains of identified MUs from each muscle, and measured the root mean square difference of the correlation coefficients between the trials of the same session (intra-session variability) and between different sessions (inter-session variability) in each participant (intra-person comparison) and across participants (inter-person comparison). In the intra-person comparison, the inter-session variability was higher than the intra-session variability, either before or after the bed rest. At 60% MVC torque, the young demonstrated higher inter-person variability of coactivation than the older participants, but this variability decreased significantly after the bed rest. In older participants, inter-person variability was consistently lower at 60% than at 30% MVC torque. In young participants, inter-person variability became lower at 60% than at 30% MVC torque only after the bed rest. Precaution is required when analyzing the MU discharge and coactivation patterns, as individual persons demonstrate individual adaptations to aging or bed rest.
Ključne besede: high density electromyography, muscle disuse, motor units, discharge rate, aging
Objavljeno v DiRROS: 05.09.2022; Ogledov: 1897; Prenosov: 997
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