Author(s): MCGRATH, M., BISSETT, B., FEARON, A., WADDINGTON, G., Institution: UNIVERSITY OF CANBERRA, Country: AUSTRALIA, Abstract-ID: 371

INTRODUCTION:
Enhanced autonomic nervous system (ANS) function is linked to superior athletic performance, commonly indexed via heart rate variability (HRV).1 However, HRV provides limited ability to distinguish parasympathetic (PNS) from sympathetic (SNS) activity.2 The pupil light reflex (PLR) may offer an alternative, providing independent measures of PNS and SNS activity.3 No studies have examined whether PLR-derived resting ANS profiles predict functional performance. Characterising this relationship may offer a rapid, non-invasive tool for monitoring movement readiness or early physiological dysfunction. The aim of this study was to investigate whether resting ANS profiles, indexed through the PLR, are associated with performance on standardised functional movement assessments.
METHODS:
90 healthy, physically active adults (age 20–88) participated. ANS activity was measured using the PLR: PNS function via maximum pupil constriction velocity and SNS function via average pupil dilation velocity. Using z scores derived from published normative PLR data, participants were categorised into one of four resting ANS profiles: Coactivation, Co inhibition, PNS dominant, or SNS dominant. Participants then completed Timed Up and Go (TUG), Six Minute Walk Test (6MWT) and Five Times Sit to Stand (5xSTS). One way ANOVAs (Jamovi v2.7.12) with Tukey post hoc comparisons examined differences across ANS profiles for each functional outcome measure. Complimentary Bayesian analyses were performed given unequal group sizes. Statistical significance set at p<0.05.
RESULTS:
Across the sample (Co-inhibition n=9; Coactivation n=35; PNS-dominant n=26; SNS-dominant n = 20), the Co-inhibition profile was associated with poorer functional performance. Co-inhibition participants demonstrated significantly slower TUG times compared to with coactivation (mean difference=1.12s, p=0.05, BF₁₀=8.39). For 6MWT, Co-inhibition participants walked significantly shorter distances than Coactivation profile (mean difference=-108m; p<0.01; BF₁₀=16.05) and PNS-dominant profile (mean difference = -89 m; p=0.05; BF₁₀=10.35). For 5xSTS, Co-inhibition was slower than Coactivation (mean difference=2.14s; p=0.08; BF₁₀=2.07), although this did not reach statistical significance.
CONCLUSION:
The results demonstrate a performance deficit in the Co inhibition profile across three standardised functional tests, thus inhibition in both branches of the ANS system at rest may be a limiting factor in functional performance. Measuring ANS balance via the PLR could reveal obscured underlying factors contributing to performance deficits. Limitations include unequal group sizes, reflecting the natural distribution of ANS profiles, which precluded an a priori power calculation. Although the Co-inhibition group was older on average, older adults were present in other ANS profiles, indicating that age alone is unlikely to explain the observed differences. References: 1. Bellenger et al. (2016); 2. Hayano & Yuda (2019); 3. Mathôt (2018).