lf

Low Frequency Power (0.04-0.15 Hz)

Definition

Low frequency power (0.04-0.15 Hz). Formally: integral(PSD; 0.04; 0.15) Hz.

What does normal look like?

Fitted normative prior: Gamma(α = 0.8676, θ = 705.1), KS p = 4.7e-118, n = 61715.

Empirical distribution over the pooled nsrdb+nsr2db normative windows (360-beat windows, 120-beat stride), overlaid with the fitted Gamma prior density. Vertical lines mark the median and the 5–95% range.

Normal-range summary (pooled nsrdb+nsr2db)

n varies by feature only through per-window validity over the full pooled nsrdb+nsr2db table (n up to 61 715; e.g. sampen/mse drop windows where the statistic is undefined). ulf is the one exception: a 360-beat (~5 min) window contains no ULF-band power, so it uses a long-window NSRDB-only extraction (see its own page).

Use cases

• Mixed sympathetic/parasympathetic and baroreflex-mediated 0.04–0.15 Hz rhythms.
• Baroreflex and blood-pressure-coupling studies.
• Interpret in normalised units rather than as pure "sympathetic" power.

Applications by area

Evidence is reported at the measure-family level; a specific variant may not be the exact index measured in every cited study.

Clinical

Coverage: statistics. A pooled literature; reviews or meta-analyses exist.

LF, HF and total power are consistently reduced in disease states (cardiac mortality risk, depression, anxiety, T2DM autonomic neuropathy) across large meta-analyses, but the LF/HF ratio itself is repeatedly non-significant in the very same datasets where its components move significantly, undercutting its billing as the most sensitive "sympathovagal balance" composite.

Dominant reported direction: down: LF/HF/TP reduced in disease; the LF/HF ratio specifically is often null.

Key references: (Rueda-Ochoa et al., 2024); (Wu et al., 2023); (Chalmers et al., 2014).

Sports & peak performance

Coverage: statistics. A pooled literature; reviews or meta-analyses exist.

Heavily used for training-load/overreaching monitoring, anchored by a 27-study meta-analysis; the intuitive "LF up / HF down under overload" model is directly contradicted by a body of work reporting paradoxical parasympathetic hyperactivity in overreached athletes, and the popular LF/HF > 4 "overtraining" cutoff is shown to be driven mainly by spontaneous breathing frequency rather than training state.

Dominant reported direction: contested: sympathetic-dominance model vs. parasympathetic-hyperactivity counter-evidence, confounded by respiration.

Key references: (Bellenger et al., 2016).

Contemplative practice

Coverage: statistics. A pooled literature; reviews or meta-analyses exist.

Commonly measured but shows null-to-mixed effects: the most direct meta-analysis (4 pooled trials) found no significant LF/HF change, and a well-powered 10-day mindfulness RCT likewise found no HF/LF-HF effect even though RMSSD rose: individual intensive-retreat studies show more mixed, technique- and task-dependent patterns confounded by voluntary breath-rate change.

Dominant reported direction: null-to-mixed, confounded by breathing.

Key references: (Rådmark et al., 2019).

See the effect-distribution meta-analysis page for the harvested per-study effect sizes/p-values behind these domain summaries (docs/zoo_gen/effect_stats.csv).

Resources

Resource-intensity rank ◍◍◍◌◌ moderate is measured: median wall-clock time and allocations over a 360-beat window on synthetic realistic RR (docs/zoo_gen/bench_resources.jl; full grid in resource_bench.csv).

Cold = fresh memoization caches (builds every shared representation from scratch); warm = shared representations (diff, periodogram, Poincaré coords, DFA fluctuation) already cached, so only this feature is recomputed. The tier is derived from the cold cost; see Frequency subgraph (requires a Welch/Lomb–Scargle periodogram first). Warm (shared representation cached) is 9× cheaper.

Citation

Akselrod et al. (1981) / Task Force (1996) LF band (0.04–0.15 Hz); Moody (1993) applied the least-squares periodogram to un-resampled HR.

Seminal reference(s): (Akselrod et al., 1981); (Task Force, European Society of Cardiology / North American Society of Pacing & Electrophysiology, 1996); (Moody, 1993).

See the References page for the full bibliography.