With the fact that no two runners respond to the same training in the same way, endurance training is as much art as it is science. That’s why having a good coach is priceless. Quantifying how hard you’re training with heart rate or the traditional constituents of training (mileage, intensity, frequency) measures the effort put into training but doesn’t assess the actual response. Just like measuring how much gas you put in your car doesn’t tell you exactly how far you can drive it before it runs out of gas (that depends on engine performance and how you drive the car), knowing that you ran 40 miles in a week doesn’t really tell you if you’ll end up running a faster marathon.
If only training adaptation was as simple as an equation: training + nutrition + sleep + life stress + everything else = adaptation. If it was that straightforward, changing one or more of those variables should result in improvements in fitness. But unfortunately it’s not that clear-cut and much of the research into genetics and exercise is devoted to understanding what separates the training “responders” from the “non-responders.”
While the variables that respond (or not) to training and constitute endurance performance—VO2max, lactate threshold, running economy—can be measured in a laboratory, they typically aren’t readily available to the average runner.
The answer to this need to quantify the effects of training on the body may be something called heart rate variability (HRV), a newly accessible means of assessing performance improvement and recovery state. HRV reflects the input of the heart’s automatic regulation and is a measure of the time gap between heartbeats, usually assessed while resting or sleeping. The heart accelerates during inhalation and slows down during exhalation and this difference is known as HRV. Research has linked a high HRV—larger time gap between heart beats—to positive adaptation and fitness, while a smaller time gap or HRV is linked to fatigue, overreaching and overtraining.
HRV can also be used to determine the training response to specific types of training. In a 2016 study, presented in Medicine and Science in Sports and Exercise, researchers examined the effects of an 8-week HRV guided running program on running performance. Forty recreational endurance runners were divided into an HRV-guided experimental training group and a traditional, predefined training group (trained according to a predefined training program that included 2-3 moderate/high intensity training sessions/week). For the experimental HRV group, the timing of higher intensity training was based solely on HRV, measured every morning. If the subject’s HRV was within a normal, acceptable range, higher intensity workouts were programmed. If HRV fell outside that range, low intensity training was performed.
The researchers found that after the 8-week training period only the HRV-guided training group improved its performance in a 3000m running trial, even though they performed less moderate and high intensity training sessions compared with the predefined training group. The study concluded that, “The timing of moderate and high intensity training sessions according to HRV is more optimal compared to subjectively predefined training.” In other words, following a training plan out of a book or off of a website may not optimally improve performance.
Similarly, HRV shows promise in identifying what types of exercise are individually optimal before an exercise program is started. In another study, published in the Scandinavian Journal of Medicine and Science in Sports in 2015, researchers measured the response of recreational runners to either high volume or high intensity training. By assessing HRV before the training period started, the researchers hoped to better understand how individuals would respond to different intensities and amounts of exercise.
After the 16-week program had concluded, the study determined that the runners with a higher HRV improved to a greater degree with high-intensity training while those with a lower HRV responded better to a higher training volume rather than training intensity. The researchers concluded, “HRV may be used to individualize endurance training in recreational endurance runners, especially to adjust training volume and intensity, to achieve greater improvements in endurance performance.”
Basically, HRV may hold the key to telling runners how to train for maximum gain before they start a training program. Having a high HRV may indicate that you can take a greater dose of high intensity training. A low HRV may be a red flag, or at least a yellow one, warning that long, slow distance training is needed. Wouldn’t you like to know the most efficient way to train for your next race?
The lead author of both of the above studies, Dr. Ville Vesterinen of Finland’s Research Institute for Olympic Sports, recommends that 3-4 HRV assessments per week be used to achieve a good, overall view of the current training status. “Given the large day-to-day variation, it is better to use long-term (e.g. 7-day) trends rather than one single HRV value. It is also essential to standardize the assessment protocol—time of day, length of measurement—to ensure good quality information.”
Measuring heart rate variability used to require complicated cardiac monitoring. Now, all it takes is a smart phone that uses any one of a number of apps —ithlete and Emfit QS to name two—to analyze heart-rate information and you have HRV information at your fingertips.
A greater understanding of HRV may very well take the guesswork out of training. Instead of the hit or miss method of trying different programs to determine which one makes you the fastest, the information gleaned from HRV could turn you from a non-responder to a responder.
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