Heart rate variability changes associated with wetsuit hood fit in dry conditions: a pilot exploratory study.

BACKGROUND

This pilot study explored whether wearing wetsuit hoods is associated with short-term changes in heart rate variability (HRV)-derived indices under controlled dry laboratory conditions.

METHODS

Eleven healthy male military participants underwent HRV recordings across four fixed-sequence conditions (Baseline, White, Blue, Yellow), administered in an order corresponding to different nominal hood sizes and expected levels of fit. RR recordings were acquired using the Polar H10 sensor and processed in Kubios HRV Premium with standardized artifact correction (medium filter), yielding normal-to-normal (NN) intervals for analysis. HRV measures included SDNN, RMSSD, pNN50, and Kubios-derived PNS/SNS composite indices. Mechanical compression was not directly measured; exploratory analyses considered hood fit using geometric mismatch proxies.

RESULTS

Several HRV-derived indices differed significantly across conditions (SDNN p = 0.036, RMSSD p = 0.011, pNN50 p = 0.004; PNS p = 0.034; SNS p = 0.049). The most consistent pattern involved reductions in RMSSD and pNN50 under hooded conditions, together with changes in composite Kubios-derived indices. Relative metrics (%PNS/%SNS) remained unchanged. Exploratory analyses suggested possible associations between hood fit and selected HRV-derived measures; however, continuous-strain analyses did not identify a robust dose-response relationship, and within-subject variation was confounded by experimental sequence order.

CONCLUSIONS

Under controlled dry laboratory conditions, wearing wetsuit hoods was associated with differences in selected HRV-derived indices. These findings should be interpreted as exploratory and hypothesis-generating rather than mechanistic, as the present design does not permit attribution to specific physiological pathways. Future studies incorporating randomized designs, direct pressure measurements, and respiratory monitoring are required to clarify the reproducibility and physiological basis of hood-associated HRV changes.