Is HRV good for energy & vitality?

The evidence points that way, though it's not yet conclusive. 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. That's reflected in an evidence score of 70/100 for its role in energy & vitality, drawn from 9 studies (5 RCTs), with an estimated impact on longevity rated moderate (50/100).