Remote Ischemic Conditioning and Spinal Reflex Modulation

Overview

Remote ischemic conditioning (RIC) is a clinically feasible method that protects distant organs from severe injury through brief, sub lethal periods of ischemia followed by re-perfusion. Recent studies suggest that RIC, combined with training, improves muscle strength and balance in healthy adults and post-stroke survivors. While the underlying mechanisms are not fully understood, RIC's neuroprotective effects - such as promoting angiogenesis, neurogenesis, and modulating glutamate and GABA synthesis - overlap with neuroplasticity processes. Evidence indicates that neuroplasticity from exercise training occurs not only in the cerebral cortex but also within the spinal cord, yet the role of spinal reflex mechanisms underlying the benefits of RIC remains under explored. Therefore, this study aims to investigate effects of RIC on spinal reflex modulation in healthy adults, both independently and combined with balance training.

Ischemic conditioning (IC) is an endogenous phenomenon that protects target organs from severe ischemic events by applying alternating cycles of brief, sublethal ischemia followed by reperfusion. Remote ischemic conditioning (RIC) is a more feasible, non-invasive method of delivering IC. It involves using a standard blood pressure cuff on either the arm or leg to induce brief periods of sublethal ischemia. Extensive evidence from both animal and human studies indicates that RIC provides neuroprotection through multifactorial mechanisms involving inflammatory, oxidative, excitotoxic, metabolic, vascular, and glial pathways. Additionally, several studies demonstrate the involvement of peripheral somatosensory, spinal cord, and autonomic pathways in RIC-induced neuroprotection. Prior research also shows that RIC enhances motor learning (balance performance) when paired with motor training in both young and older adults. While a wealth of research has shown that neuroplasticity in response to training occurs in cortical and spinal neural circuits, limited studies have explored the effects of RIC on spinal modulations in healthy adults. Notably, only one study has reported a reduction in Hoffman (H)-reflex amplitudes with RIC. Given the evidence of peripheral neuronal pathways involved in RIC and its positive impact on balance performance, it is plausible that RIC could lead to spinal reflex modulations and enhance balance improvements in healthy adults. These modulations may be further amplified when RIC is combined with balance training. The specific aims of this study are to determine whether 1) remote ischemic conditioning (RIC) combined with balance training modulates spinal reflex excitability, as reflected by H-reflex measures, and 2) to examine whether RIC combined with balance training leads to greater improvements in balance performance compared to sham conditioning combined with training in healthy adults. In this single-blind, randomized controlled trial, 30 healthy adults aged 18-40 years will undergo H-reflex testing of the dominant lower extremity and balance assessments at baseline (pre-training). Participants will then be randomized to receive either RIC or sham conditioning combined with a 5-day balance training program. RIC or sham conditioning will be delivered using cyclic inflation and deflation of a pressure cuff applied to the thigh of the dominant lower extremity following a standardized protocol. Balance training will consist of standing on a stability platform with the goal of maintaining the platform within a 5-degree horizontal range for 30 seconds across 15 trials per day for five consecutive days. All outcome measures, including H-reflex parameters (Hmax, maximal H-reflex amplitude, and Hmax/Mmax ratio) and balance performance, will be reassessed post-training following completion of the 5-day intervention. It is hypothesized that, compared to sham conditioning combined with balance training, RIC combined with balance training will result in greater reductions in H-reflex excitability and greater improvements in balance performance from baseline to post-training. This study will help clarify whether RIC induces alterations in spinal reflex modulations when applied independently or in combination with motor training, thereby reflecting neuroplasticity within the spinal cord in healthy young adults. These findings would deepen our understanding of the spinal mechanisms underlying the benefits of RIC and could accelerate its translation for individuals with neurological disorders