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Purpose <p>This randomized, participant-blinded, sham-controlled 2 × 2 crossover trial examined whether a 4-week intermittent normobaric hypoxia intervention performed at rest (IHNT; 12 sessions; FiO₂ ≈ 0.12) is associated with changes in indices of cardiac parasympathetic modulation in master cyclists.</p> Methods <p>Twenty-three master cyclists aged 50–60 years completed both IHNT and normoxic sham conditions across two periods with a 4-week washout. HRV was assessed from standardized supine morning recordings summarized as 7-day means at Baseline, Post-intervention, and Follow-up. Primary outcomes were lnRMSSD and lnHF, analyzed using linear mixed-effects models with autoregressive residual structure, condition-specific heterogeneous variances, and Holm-adjusted contrasts.</p> Results <p>Significant Condition × Time interactions were observed for lnRMSSD (χ²(2) = 16.27, <i>p</i> &lt; 0.001) and lnHF (χ²(2) = 18.18, <i>p</i> &lt; 0.001), reflecting divergent autonomic trajectories across conditions. Within IHNT, lnRMSSD increased by + 13.6% (<i>p</i> &lt; 0.001) and lnHF by + 17.9% (<i>p</i> &lt; 0.001) Post-intervention, with partial retention at Follow-up (+ 4.5% and + 7.0%, respectively). Sham showed significant lnHF decreases at Post (− 20.5%) and Follow-up (− 21.3%; both <i>p</i> = 0.030), while lnRMSSD remained stable. Pairwise between-condition contrasts did not reach significance after Holm–Bonferroni adjustment. A baseline-adjusted sensitivity analysis confirmed the lnHF interaction (χ²(1) = 12.04, <i>p</i> &lt; 0.001). Blinding was maintained (52.4% accuracy, <i>p</i> = 0.287).</p> Conclusion <p>IHNT at rest was associated with divergent cardiac autonomic trajectories versus sham in master cyclists, with consistent within-IHNT increases in parasympathetic indices and concurrent vagal withdrawal under sham. These proof-of-concept findings support a physiological signal warranting confirmation in adequately powered trials.</p> Graphical abstract <p></p>

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Intermittent normobaric hypoxia at rest is associated with divergent cardiac autonomic trajectories in master cyclists

  • 期刊论文

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  • 发表日期：

    2026年5月29日

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  • Pedro Navarro-Gómez

摘要

Purpose

This randomized, participant-blinded, sham-controlled 2 × 2 crossover trial examined whether a 4-week intermittent normobaric hypoxia intervention performed at rest (IHNT; 12 sessions; FiO₂ ≈ 0.12) is associated with changes in indices of cardiac parasympathetic modulation in master cyclists.

Methods

Twenty-three master cyclists aged 50–60 years completed both IHNT and normoxic sham conditions across two periods with a 4-week washout. HRV was assessed from standardized supine morning recordings summarized as 7-day means at Baseline, Post-intervention, and Follow-up. Primary outcomes were lnRMSSD and lnHF, analyzed using linear mixed-effects models with autoregressive residual structure, condition-specific heterogeneous variances, and Holm-adjusted contrasts.

Results

Significant Condition × Time interactions were observed for lnRMSSD (χ²(2) = 16.27, p < 0.001) and lnHF (χ²(2) = 18.18, p < 0.001), reflecting divergent autonomic trajectories across conditions. Within IHNT, lnRMSSD increased by + 13.6% (p < 0.001) and lnHF by + 17.9% (p < 0.001) Post-intervention, with partial retention at Follow-up (+ 4.5% and + 7.0%, respectively). Sham showed significant lnHF decreases at Post (− 20.5%) and Follow-up (− 21.3%; both p = 0.030), while lnRMSSD remained stable. Pairwise between-condition contrasts did not reach significance after Holm–Bonferroni adjustment. A baseline-adjusted sensitivity analysis confirmed the lnHF interaction (χ²(1) = 12.04, p < 0.001). Blinding was maintained (52.4% accuracy, p = 0.287).

Conclusion

IHNT at rest was associated with divergent cardiac autonomic trajectories versus sham in master cyclists, with consistent within-IHNT increases in parasympathetic indices and concurrent vagal withdrawal under sham. These proof-of-concept findings support a physiological signal warranting confirmation in adequately powered trials.

Graphical abstract