HRV-guided training

Heart rate variability monitoring for athletes

Heart rate variability (HRV) reflects fluctuations in the intervals between consecutive heartbeats, providing insight into cardiac autonomic function and overall physiological state. Endurance athletes typically demonstrate superior cardiac autonomic function compared to non-athletes, characterized by lower resting heart rates and greater resting HRV. Gradual increases in resting HRV have been linked to improved aerobic fitness and performance ^[1].

The availability and use of HRV metrics have increased due to the ease of access to monitoring tools. Athletes, coaches, and sports medicine staff commonly collect HRV data, with daily resting HRV measurements taken in the morning often recommended. Selecting the appropriate HRV parameter for monitoring athletes’ physiological state is crucial. RMSSD is the most commonly used parameter because it reflects cardiac vagal regulation, is not affected by respiratory rate (unlike HF power), and is simple to calculate. However, RMSSD has a limitation, where reduced HRV can sometimes be observed despite a low resting HR due to HRV saturation ^[2]. This limitation can be addressed by using the PNS index, which accounts for resting heart rate.

How training affects HRV

The impact of training on resting HRV is individual and influenced by factors such as training status, cardiorespiratory fitness, age, and sex. Regular aerobic training typically increases HRV in athletes. However, increased exercise duration can elevate the overall training load and acutely decrease daily HRV. Exercise intensity, on the other hand, impacts HRV scores either immediately or the day after exercise. ^[3]

Cardiac-autonomic functioning, assessed via daily resting HRV measurements, serves as a non-invasive marker of acute and chronic adaptation to endurance exercise. In the short term (within 48 hours after exercise), HRV recovery to baseline coincides with the restoration of thermoregulatory, metabolic, hemodynamic, and fluid-balance processes disrupted by physical exertion. Long-term HRV profiles reflecting higher and/or more stable resting values are associated with greater improvements in post-intervention fitness outcomes among sedentary, moderately-trained, highly-trained, and clinical populations. ^[4]

HRV-guided training protocol

HRV-guided training protocols involve tailoring workout intensity based on daily heart rate variability readings to optimize performance and recovery. When the HRV score is within or above the athlete’s normal range, moderate to high-intensity workouts are recommended. Conversely, when the HRV score is below the normal range, lower intensity activities or rest days are advised. This personalized approach helps balance training stress and recovery, minimizing the risk of overtraining, and enhancing overall athletic performance. The Kubios HRV app provides validated means for daily HRV measurement and can be used free of charge by athletes to assess daily recovery status, ensuring effective HRV-guided training.

An example HRV-guided training protocol is presented in the figure below. The basic idea is to lower the training intensity whenever the daily HRV score decreases and not to allow more than two consecutive high-intensity exercises or rest days.

Effectiveness of HRV-guided training

HRV-guided training has been validated against predefined training in several studies ^{[4], [6], [7]}. These studies have shown that HRV-guided training is effective, associated with improved submaximal performance, better or similar overall performance and physical fitness, and fewer non-responders. Additionally, the benefits of HRV-guided training are typically achieved with a reduced amount of moderate and/or high-intensity training.

In summary, HRV-guided training is an accessible and individualized exercise prescription strategy that may be more effective than predefined training for maintaining and improving performance, with a lower likelihood of negative responses. Daily monitoring of HRV allows athletes to adjust their training day-by-day and observe changes in their physiological state. With the Kubios HRV Team Readiness dashboard, coaches can also leverage HRV data to tailor training programs for their athletes. Gradual increases in average HRV correspond with improved overall physiological performance, aerobic fitness, high functional state, readiness to train, and recovery ability. Conversely, decreasing HRV has been associated with maladaptive states, including illness, non-functional overtraining, and, in the worst case, overtraining.