Cardiometabolic Effects of High-Intensity Hybrid Functional Electrical Stimulation Exercise after Spinal Cord Injury

Electrical stimulation for the treatment of spinal cord injuries: A review of the cellular and molecular mechanisms that drive functional improvements

Spinal cord injury (SCI) is a devastating condition that causes severe loss of motor, sensory and autonomic functions. Additionally, many individuals experience chronic neuropathic pain that is often refractory to interventions. While treatment options to improve outcomes for individuals with SCI remain limited, significant research efforts in the field of electrical stimulation have made promising advancements. Epidural electrical stimulation, peripheral nerve stimulation, and functional electrical stimulation have shown promising improvements for individuals with SCI, ranging from complete weight-bearing locomotion to the recovery of sexual function. Despite this, there is a paucity of mechanistic understanding, limiting our ability to optimize stimulation devices and parameters, or utilize combinatorial treatments to maximize efficacy. This review provides a background into SCI pathophysiology and electrical stimulation methods, before exploring cellular and molecular mechanisms suggested in the literature. We highlight several key mechanisms that contribute to functional improvements from electrical stimulation, identify gaps in current knowledge and highlight potential research avenues for future studies.

Hybrid Functional Electrical Stimulation improves anaerobic threshold in first three years following spinal cord injury

The purpose of the present investigation was to assess the effects of whole-body exercise on anaerobic threshold in individuals with spinal cord injury (SCI). Maximal oxygen uptake (VO2max) and oxygen uptake at anaerobic threshold (AT) were measured before and after 6 months of hybrid functional electrical stimulation row training in 47 participants with SCI aged 19-63, neurological levels of injury C4-L1, American Spinal Injury Association Impairment Scale grades A-D, and time since injury at enrollment from 3 months to 40 years. Changes in VO2max differed with time since injury, with greater increases earlier post injury. The early chronic group (<3 years since injury; n=31) increased VO2max from 1.65 ± 0.54 L/min at baseline to 1.83 ± 0.66 L/min at 6 months (p<0.05), while the late chronic group (>3 years since injury; n=16) did not change (1.42 ± 0.44 at baseline to 1.47 ± 0.41 L/min at 6 months, p=0.36). Consistent with VO2max changes, AT increased in the early chronic group (1.03 ± 0.31 to 1.20 ± 0.40 L/min, p<0.05) and did not change in the late chronic group (0.99 ± 0.31 to 0.99 ± 0.26 L/min, p=0.92). Cumulative duration of exercise training was positively correlated to change in VO2max (r=0.475, p<0.05) but not to change in AT. Hybrid functional electrical stimulation row training is effective for increasing aerobic capacity and anaerobic threshold in individuals with spinal cord injury; however, these fitness benefits are only significant in individuals initiating the exercise intervention within three years of injury.

Effect of hybrid FES exercise on body composition during the sub-acute phase of spinal cord injury

Objectives

To determine the Effect of Hybrid functional electrically stimulated (FES) Exercise on Body Composition during the Sub-acute Phase of Spinal Cord Injury (SCI).

Design

Randomized Clinical Trial.

Setting

Rehabilitation Hospital.

Participants

Patients within sub-acute phase (3–24 months) of SCI.

Interventions

We investigated if high-intensity exercise training via the addition of functional electrically stimulated (FES) leg muscles, provides sufficient stimulus to mitigate against body composition changes in the sub-acute phase after SCI.

Main outcome measures

We explored potential effects of FES row training (FESRT) on body fat gain, lean mass loss, and cardiometabolic parameters and compared the effects of 6-month of FESRT (n = 18) to standard of care (SOC, n = 13). Those in SOC were crossed over to FESRT.

Results

FESRT resulted in greater exercise capacity and a tendency for lesser total body fat accumulation with a significant increase in total and leg lean mass (p<0.05). In addition pelvis and total bone mineral density declines were significantly less (p<0.05). Compared to SOC, FESRT did not lead to any significant difference in insulin sensitivity or serum lipids. However, HbA1C levels were significantly decreased in SOC participants who crossed over to 6-month FESRT.

Conclusion

FESRT early after SCI provides a sufficient stimulus to mitigate against detrimental body composition changes. This may lead to prevention of losses in lean mass, including bone.

Virtual Strategies for the Broad Delivery of High Intensity Exercise in Persons With Spinal Cord Injury: Ongoing Studies and Considerations for Implementation

Spinal cord injury (SCI) results in a multitude of metabolic co-morbidities that can be managed by exercise. As in the non-injured population, manipulation of exercise intensity likely allows for fruitful optimization of exercise interventions targeting metabolic health in persons with SCI. In this population, interventions employing circuit resistance training (CRT) exhibit significant improvements in outcomes including cardiorespiratory fitness, muscular strength, and blood lipids, and recent exploration of high intensity interval training (HIIT) suggests the potential of this strategy to enhance health and fitness. However, the neurological consequences of SCI result in safety considerations and constrain exercise approaches, resulting in the need for specialized exercise practitioners. Furthermore, transportation challenges, inaccessibility of exercise facilities, and other barriers limit the translation of high intensity “real world” exercise strategies. Delivering exercise via online (“virtual”) platforms overcomes certain access barriers while allowing for broad distribution of high intensity exercise despite the limited number of population-specific exercise specialists. In this review, we initially discuss the need for “real world” high intensity exercise strategies in persons with SCI. We then consider the advantages and logistics of using virtual platforms to broadly deliver high intensity exercise in this population. Safety and risk mitigation are considered first followed by identifying strategies and technologies for delivery and monitoring of virtual high intensity exercise. Throughout the review, we discuss approaches from previous and ongoing trials and conclude by giving considerations for future efforts in this area.