HRV

Research summary

• A 2017 meta-analysis found HRV biofeedback training — deliberately practicing slow, paced breathing to increase heart rate variability — produces a meaningful reduction in self-reported stress and anxiety, a mechanism-consistent finding supported by a separate meta-analysis showing voluntary slow breathing reliably increases HRV.
• On the training side, a methodological systematic review and meta-analysis found HRV-guided training (adjusting workout intensity day-to-day based on morning HRV readings) improves cardiac-vagal modulation, aerobic fitness and endurance performance compared with fixed training plans, a finding reinforced by several more recent randomized trials in both healthy runners and cardiac rehabilitation patients.
• An older systematic review found resting heart rate is a reasonably convenient, if imperfect, tool for monitoring overreaching in athletes.
• Together this supports HRV as a genuinely useful, evidence-backed signal for both stress management and training regulation, though individual variability in HRV readings means it works best as one input among several rather than a sole decision-making tool.