The effect of continuous aerobic ergometer kayak training (CAEKT) versus to high-intensity interval training (HIIT) on heart rate variability in individuals with spinal cord injury.

Abstract

INTRODUCTION: Spinal cord injury (SCI) is associated with cardiovascular autonomic dysfunction, impaired sympathetic-vagal regulation, and an increased risk of cardiovascular complications. Heart rate variability (HRV) is a useful noninvasive tool for assessing autonomic modulation and exploring the physiological response to exercise in this population.

OBJECTIVE: To compare the effect of continuous aerobic kayak ergometer training (CAEKT) versus high-intensity interval training (HIIT) on HRV and the cardiovascular autonomic profile in individuals with SCI.

METHODS: A randomized, assessor-blinded clinical trial was conducted in adults with SCI. Eligibility criteria were a diagnosis of SCI of any etiology, a functional neurological level below C8, age over 18 years, and time since injury of more than 6 months. Participants were randomly assigned to one of two training programs. HRV was analyzed using time-domain indices and autonomic variables derived from Kubios software, including SDNN, RMSSD, Mean RR, Mean HR, Stress Index, PNS index, and SNS index.

RESULTS: The sample comprised 14 individuals; 13 had complete data for most variables. After the training period, SDNN increased from 32.12 ± 9.67 ms to 42.15 ± 9.18 ms (p < 0.001), the PNS index improved from −0.69 ± 1.02 to −0.07 ± 0.66 (p = 0.019), and the SNS index decreased from 1.80 ± 2.07 to 0.70 ± 1.04 (p = 0.048), with no significant time × group interaction. Individual analysis revealed a heterogeneous response, with several participants showing increased Mean RR and RMSSD, decreased heart rate, and a reduced Stress Index.

CONCLUSIONS: Both continuous aerobic kayak ergometer training and high-intensity interval training were associated with an overall improvement in cardiovascular autonomic modulation, with no evidence of statistical superiority of one modality over the other in this sample. These findings support the usefulness of HRV as a relevant physiological outcome in rehabilitation.