Letter to the editor regarding to “autonomic recovery following submaximal exercise in yoga practitioners versus aerobic and strength-trained individuals”

We read with interest the article by Sreenath et al. on autonomic recovery after a submaximal Harvard Step Test in long-term yoga practitioners versus aerobic- and resistance-trained adults. We commend the authors for a direct head-to-head comparison and for using short-term HRV segments in line with common practice [1]. However, several issues warrant further discussion.

First, the primary between-group finding is higher recovery HF power in the yoga group. Yet HF power is strongly driven by respiratory rate and tidal volume; slow-paced breathing can increase HF power even without broader improvements in autonomic control. This is particularly pertinent because the yoga curriculum in this study includes pranayama, and participants may have spontaneously adopted slower breathing during recovery. Without measuring (or standardizing) respiration during the 5-min recovery segment, it is difficult to interpret HF differences as vagal “reactivation” rather than differential breathing patterns. This concern is well recognized in HRV standards and interpretation papers, which emphasize respiration as a major determinant of HF-related indices and caution against over-interpreting HF without respiratory context [2]. Clinically, this matters: we could mistakenly conclude that yoga uniquely accelerates physiologic recovery, when the observed signal may be a breathing-mediated phenomenon that could be taught across modalities.

Second, the authors operationally define recovery as the absolute HRV values in a selected post-exercise 5-min segment, not the change from baseline. In rehabilitation practice, “recovery” typically reflects kinetics (e.g. slope, time constant) or return toward baseline, not simply the magnitude at a single post-exertion window. Given marked inter-individual variability in resting HRV and in the immediate post-exercise suppression pattern, comparing absolute post-exercise values, then adjusting with ANCOVA, may not capture what clinicians need: how fast autonomic indices normalize after a standardized physiological load. Reviews of post-exercise HRV highlight that recovery is time-dependent and method-sensitive; single-window summaries can yield different conclusions than trajectory-based metrics [3].

Third, although standardized externally (platform height, cadence, duration), the Harvard Step Test can generate different relative intensities depending on leg length, stepping economy, and fitness level. If internal load differed systematically by training background, HRV suppression and rebound would also differ, independent of any modality-specific autonomic “advantage.” From a rehabilitation standpoint, internal load markers (e.g. %HR reserve, VO₂ estimates, RPE, or lactate) help interpret recovery indices and translate findings to prescription. Absent such anchors, it is hard to generalize the results to clinical exercise testing or to individualized rehab dosing [4].

Fourth, both pNN50 and RMSSD are commonly treated as vagal-related time-domain indices and are often highly correlated. Observing a significant group effect for pNN50 but not RMSSD invites scrutiny: Are results sensitive to preprocessing, ectopy correction thresholds, or distributional assumptions? In sports and rehabilitation monitoring, RMSSD is frequently preferred for its relative stability and interpretability across conditions. The discordance here suggests the need for sensitivity analyses (e.g. log-transforming skewed spectral power, alternative artifact correction settings, or examining correlations among indices) before drawing practice-facing conclusions about “parasympathetic reactivation.”[5]

In summary, we agree the study supports an association between yoga participation and higher post-exercise HRV indices, but we urge caution in translating this into modality-specific claims about autonomic recovery.

Funding Statement

This study was supported by the Shanghai University of Traditional Chinese Medicine Science and Technology Development Project (Nursing Specialization).

Ethical approval

Not applicable.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

Data sharing is not applicable to this article as no new data were created or analyzed in this study.