Heart rate variability for archers: Laborde 2017

This is not an experimental study but a methods review: three psychophysiology researchers gather in one paper the choices needed to measure heart rate variability (HRV) and vagal tone properly, vagal tone being the contribution of the vagus nerve, and so of the parasympathetic system, to the control of the heart. Their starting point is that HRV is easy to record and hard to interpret, and that many findings cannot be compared because each laboratory makes different choices.

The recommendations cover planning, measurement, analysis and reporting. Among the most concrete: focus on indices of vagal tone (RMSSD, HF, the peak-valley method); set aside the LF/HF ratio as a measure of sympathetic-parasympathetic balance, because its physiological meaning is uncertain; prefer designs in which each person serves as their own control; structure the experiment in three phases, rest, reactivity and recovery; record the ECG with electrodes rather than chest straps or optical sensors; and correct artefacts by inspecting the trace, not only with an automatic filter. For 80% statistical power, according to an estimate the authors adopt, studies need 233, 61 and 21 participants to detect small, medium and large effects.

The authors collect no data: they start from the 1996 Task Force standards and later reviews and, for each stage of a study, summarise the options and justify them from the literature; a final table brings together the main recommendations. On recording length they advise 5 minutes where possible and at least 1 minute when HF is used, noting that for RMSSD much shorter windows can be enough. For the baseline they suggest sitting with knees at 90 degrees, hands on the thighs with palms up and eyes closed, after at least 5 minutes in that position. For the ECG, a minimum sampling rate of 125 Hz, with 500 Hz as the cautious choice.

Breathing should be monitored but not routinely corrected for: HF reflects vagal tone only between 9 and 24 breaths per minute, and athletes, who often breathe more slowly, can fall outside that range. On movement the authors are firm: when the body is active, vagal tone cannot be interpreted unambiguously. The supplementary material includes a form for recording the variables to control, such as sleep, coffee, meals, alcohol, the previous day's training and medication.

The authors themselves make clear that their recommendations are not a standard, and that the best choice depends on the research question. The paper is written for laboratory psychophysiology, meaning cognitive or emotional tasks done at rest and compared with a resting baseline: it says little about sport and nothing about archery. It dates from 2017, so it does not cover later work on wearable devices and ultra-short recordings. Some recommendations are still debated, for instance not correcting HRV for breathing, which the authors present as the most current position in a debate that remains open.

For archers this review says nothing about shooting, but it helps in reading the studies that use HRV on archers. Shooting involves movement, effort and held breath, precisely the conditions in which the authors warn that vagal tone cannot be read unambiguously. A study that measures HRV during ends with a chest strap, a few minutes of recording and the LF/HF ratio as a stress index therefore starts with more uncertainty than one that records the ECG at rest before and after shooting and uses RMSSD.

The same applies to anyone tracking their own HRV with an app or a watch: readings taken at the same time of day, in the same position and at rest can be compared with one another, while readings taken during training much less so. In the registry this page serves as a reference for judging the quality of methods, not as evidence on any claim about shooting.