(10) ACUTE EFFECT OF NERVE STIMULATION ON AUTONOMIC FUNCTION AND MARKSMANSHIP FOLLOWING HIGH-INTENSITY EXERCISE IN TACTICAL PERSONNEL WITH A HISTORY OF TBI

Introduction: Tactical personnel face unique physical and mental stress, which can alter the autonomic nervous system (ANS). Prior research demonstrates transcutaneous vibroacoustic stimulation (TVAS) modulates ANS activity to enable more efficient and appropriate efferent output, which may enhance operational performance. 

Purpose: To investigate whether TVAS improves marksmanship via enhanced ANS modulation following high-intensity interval (HII) exercise in asymptomatic tactical personnel with a history of TBI. 

Methods: Twenty-eight participants (M=20; F=8, age=21.0±3.4y) completed one baseline and two experimental visits. Baseline included familiarization of cognitive and human performance tasks, including marksmanship, and a VO_2max test. Experimental sessions consisting of active and sham stimulation conditions were randomized, counterbalanced, and separated by 3-7 days. During each experimental session, participants wore the ApolloNeuro™ device proximal to the lateral malleolus to deliver TVAS at specific frequencies. Participants were told they would receive vibrations of varying intensities. During the sham condition, the device was set to “Focused”, ramped-up to 50% intensity over 2.5 min, then down to 0% over 2.5 min. During the active condition, the device was set to “Focused”, ramped-up over 5 min, and maintained at 50% throughout the session. For each experimental session, participants completed cognitive and human performance tasks before and after a 20-min HII treadmill protocol composed of 1-min work intervals at 115% VO_2max interspersed with 1-min recovery intervals at 40% VO_2max. After the second round of cognitive and human performance tasks and 60-min of seated rest, participants completed a word recall and recognition task. Measures of heart rate (HR) and heart rate variability (HRV) were taken during seated rest at the beginning of each session and recorded throughout the visit using a chest strap Polar H10 HR monitor. Marksmanship was assessed using a shooting simulator with a laser-modified, gas blowback airsoft pistol. Participants were instructed to shoot 16 targets displayed at random intervals over 2-min as quickly and accurately as possible and were allowed one shot per target. Repeated measures ANOVAs were used for marksmanship, HR, and HRV with a Greenhouse Geisser correction (α=0.05). Bivariate regressions were conducted to investigate relationships between changes in HRV (HR, SDNN, RMSSD, CVNN) and shooting performance (Total Score, Average Score per Shot i.e., distance from center of mass, Hit%, Miss%, Omission%). 

Results: Active stimulation enhanced marksmanship Average Score per Shot compared to sham (P=0.02). Across all timepoints, active stimulation led to a greater HR (P=0.03) and a greater reduction in RMSSD (P=0.04) compared to sham. Changes in SDNN and CVNN between active and sham were negatively associated with Average Score per Shot (r≥-0.38). 

Conclusion: Active TVAS increased HR, reduced RMSSD, and improved marksmanship relative to sham. Thus, TVAS significantly affected the ANS during marksmanship following intense exercise. Future studies should explore the impact of variations in frequency and intensity on ANS activity and human performance. PRACTICAL APPLICATION: TVAS represents a promising tool to optimize ANS activity and enhance tactical-task performance following high exertion activities. TVAS applications may extend to other physically and cognitively demanding tasks or occupations.

Acknowledgements:

This abstract was made possible in part by Grant Number T32-GM081740 from NIH-NIGMS. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIGMS or NIH.