Background: High-intensity interval training (HIIT) imposes substantial autonomic and metabolic stress, potentially compromising recovery and adaptive capacity. Yoga, through pranayama (breath control) and asana (physical postures), has been proposed to enhance parasympathetic tone and accelerate recovery, yet empirical evidence from sham-controlled trials in athletic populations remains limited.

Objective: This study investigated the specific effects of a 12-week pranayama and asana intervention on autonomic nervous system regulation, heart rate variability (HRV), and recovery markers in athletes engaged in regular HIIT, relative to an attention-matched sham control.

Methods: One hundred twenty trained athletes were randomised to either a Yoga + HIIT group (n = 60) or a Sham Control + HIIT group (n = 60). A priori power analysis indicated this sample provided 80% power to detect a moderate effect (Cohen’s d = 0.50) in HRV parameters at α = 0.05. The Yoga group performed 30 minutes of supervised pranayama and asana practice three times weekly immediately following HIIT sessions. The Sham group received an equivalent duration of non-yogic static stretching, neutral breathing, and supine rest, matched for attention, social interaction, and session structure. Both groups maintained equivalent HIIT training loads (monitored via session RPE and duration). Assessments at baseline, 6 weeks, and 12 weeks were conducted by assessors blinded to group allocation. Primary outcomes were time-domain HRV indices (RMSSD, SDNN, pNN50), with respiratory rate recorded and controlled as a covariate to prevent respiratory confounding. Secondary outcomes included frequency-domain HRV (interpreted cautiously), resting heart rate, heart rate recovery, salivary cortisol (collected at standardized waking times with menstrual cycle phase controlled in females), subjective recovery, sleep quality, perceived exertion, and 3000m time trial performance. The Benjamini–Hochberg false discovery rate (FDR) procedure-controlled Type I error across primary outcomes. Missing data were addressed via multiple imputation under an intent-to-treat framework. Causal mediation analysis (bootstrapped) examined whether HRV changes mediated recovery outcomes.

Results: Intent-to-treat analysis demonstrated that the Yoga + HIIT group exhibited significant improvements in primary time-domain HRV indices compared with the Sham group after FDR correction (all q < 0.001): RMSSD (+12.4 ms vs. +3.2 ms), SDNN (+15.1 ms vs. +3.8 ms), and pNN50 (+9.2% vs. +2.1%). Respiratory rate did not differ between groups at any time point (p > 0.05), and results remained significant when respiratory rate was covaried. The Yoga group also showed superior recovery markers: resting heart rate (−6.8 bpm vs. −2.1 bpm), heart rate recovery (+7.9 bpm vs. +2.8 bpm), salivary cortisol (−5.8 nmol/L vs. −1.5 nmol/L), subjective recovery (+2.1 vs. +0.6), and sleep quality (−2.9 vs. −0.6 PSQI). Performance outcomes favored the intervention group (3000m time trial: −21.4 s vs. −7.8 s; RPE: −2.5 vs. −1.2), all q < 0.001. Mediation analysis indicated that RMSSD change significantly mediated the effect of group assignment on heart rate recovery and cortisol reduction (bootstrapped 95% CIs excluded zero). No serious adverse events occurred; adherence was 86.3% and 84.7%, respectively.

Conclusion: Integrating pranayama and asana practice with HIIT specifically enhances autonomic regulation, accelerates recovery, and improves performance beyond non-specific attention and relaxation effects in trained athletes. Yoga should be considered a structured adjunctive recovery modality in high-performance training programs, though longer-term follow-up is required to confirm the durability of benefits.