Heart Rate Variability

If you’ve been paying attention to the fitness world lately, you’ve probably heard the term heart rate variability thrown around in regards to training and recovery. In the simplest terms, heart rate variability (HRV) is the measure of time intervals between heartbeats, measuring how well our autonomic nervous system is functioning. When our bodies are stressed, the sympathetic ‘flight or fight’ branch is more active. When we’re resting, our parasympathetic ‘rest and digest’ branch is more active.

Rate of recovery is dependent on a number of variables, not just the intensity of your workout. How well you sleep, what you eat, your normal daily activities, and training levels all play a huge factor in recovery. Daily HRV measurements are thought to be an indication of how ready your body is to train. Higher variability is better and indicates that your heart is reacting well to the changes in your body. Persistently low HRV values can indicate chronic stress or overtraining. Measurements taken at the same time daily are the closest to each individual’s baseline and can identify trends in variation.

A study in Finland looked at 26 male runners randomly placed into 3 different training groups over a 4 week period of time: a standardized plan, an HRV generated individual plan, and a control group. The training group performed low intensity running exercise followed by two days of high intensity exercise two times before take a rest day. The HRV group exercised either at a high or low intensity based on their home HRV readings. The control group ran at either high or low intensity based on recommendations from the American College of Sports Medicine.

The authors measured VO2 (peak oxygen consumption) and maximal running velocity in a treadmill test before and after running. Both groups showed improvements in running speed, but the HRV group had larger improvements overall and an increased peak VO2. Additionally, the HRV group had smaller variations in improvement among group members. The authors concluded this was due to the individualized plans driven by each participants daily HRV reading. This study found that in fit individuals, an individualized plan based on daily HRV effectively improved cardiorespiratory fitness.

Want to give it a try? Here are some apps to start tracking, and watch for a follow-up blog on how to interpret your data!

Apple Health
Endurance training guided individually by daily heart rate variability measurements. Kiviniemi AM1, Hautala AJ, Kinnunen H, Tulppo MP. Eur J Appl Physiol. 2007 Dec;101(6):743-51. Epub 2007 Sep 12.

Dr. Lisbeth Hoyt, DPT