Acute effects of neuromuscular electrical stimulation on lactate, IGF-1 and cognition in chronic spinal cord injury: A pilot randomized cross-over study

Abstract

Introduction: Individuals with spinal cord injuries (SCI) exhibit an accelerated age-related cognitive decline compared to healthy individuals, even after adjusting for mood factors and concomitant traumatic brain injury. We hypothesized that neuromuscular electrical stimulation (NMES) on hamstring and gluteal muscles may induce a dose-dependent increase in lactate and insulin-like growth factor-1 (IGF-1) which is hypothesized to be associated with a temporary enhancement of cognitive performance.

Methods: Twenty-two individuals with chronic SCI participated in a randomized cross-over study, receiving NMES on one of both visits. Participants randomly underwent a single session of 30 or 60-minute NMES. Lactate, IGF-1 levels and processing speed on the Symbol Digit Modalities test (SDMT) were tested before, immediately after and 30 minutes after intervention or 60 minutes rest.

Results: Lactate levels increased significantly immediately after NMES conditions compared to control (p = 0.004). Lactate increases were larger in the 30-minute NMES group compared to the 60-minute NMES group, consistent with the higher current amplitude applied in the former (100 mA compared to 40 mA). IGF-1 increases did not significantly differ between groups (p = 0.262), and there were no significant differences in SDMT performance changes over time between groups (p = 0.892).

Conclusion: Acute NMES did not induce changes in IGF-1 levels or cognitive performance in individuals with SCI. However, 30 min of 100 mA of NMES significantly increased lactate levels, and could be used as a marker of NMES intensity in this population. Further research is required to explore various NMES protocols and their impact on cognitive domains in individuals with SCI.

Keywords: Cognitive aging; Dose–response; Lactic acid; Myokines; Neuromuscular electrical stimulation; spinal cord injury.