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Heart Rate vs. Heart Rate Variability: Endurance Sport Application, Part II

Part I, Part IA

In this post we’ll sample the literature on HRV specific to endurance sports.  As noted in previous installments, one benefit of HRV is the ability to optimize daily training.  Following a cookie-cutter template fails to account for daily variation in the athlete’s condition.  Subjective observation is useful, but loses reliability without quantitative confirmation.  HRV can help remove some guesswork in deciding what type of workout the athlete needs today.  We can still schedule in advance, but HRV gives us daily confirmation whether we’re in the right place at the right time. 

Kiviniemi (2007) compared HRV-guided training with a generic training approach for a group of twenty four moderately trained male athletes.  The two experimental groups were 1) a group following an identical training plan and 2) a group whose runners adjusted daily by HRV.  Both groups trained six days per week with 40 min daily runs.  Group  1 (training plan group) ran two days of intense running per cycle and four days light running.  Group 2 based each day’s training choice upon HRV indices.  Both groups trained four weeks. 

Result: HRV-trained group improved velocity significantly compared to the generically trained group.  This study was limited as it included only recreational runners at relatively low volume.  Further, with only four weeks of training, it is uncertain how results would persist in a longer term, and improvement is rarely linear.  Nonetheless, the data does suggest HRV has value as a daily guide for training selection. 

HRV has also been shown to coincide with non-functional overreaching (NFOR).  Remember though, overreaching is essential for growth.  Without some overreaching, no growth occurs.  When overreaching occurs in appropriate doses to stimulate adaptation, it is called functional.  When the stimulation is too great for adaptation it becomes non-functional.  Overreaching does not only depend on training stress; non-training stress also drives overreaching...and guess what can measure nontraining stress…HRV!

Plews (2012) conducted a case study with two elite triathletes (one male, one female), one of whom plunged into non-functional overreaching before a key event.  The NFOR athlete was later diagnosed with shingles.  Both athletes were similar age and trained similar volume leading up to the event.   Authors observed that HRV and the log of HRV in the NFOR athlete declined significantly during the seven days prior to the event (HRV decline typically indicates shift toward sympathetic nervous system dominance, or increase in baseline autonomic stress).  Values in the other athlete remained steady. 

Though this is only one study with two athletes, the results do match the hypothesis that HRV would be correlated with decrease in overall health.  Further, the study also shows that HRV trends may apply to both elites and recreational athletes.   Note too that Berkoff (2007) showed that elite track and field athletes tend to have higher parasympathetic tone (higher HRV) than recreational athletes, though overall fluctuation is still subject to the same external variables.      

Readiness is not only measured daily, but can apply long term.  Vesterinen (2011) studied 28 recreational endurance runners for 28 weeks to observe whether HRV could predict improvement during this training block.  Runners trained fourteen weeks of base training, and fourteen weeks intensive training.  Result: “recreational endurance runners with a high HRV at baseline improved their endurance running performance after ITP (intensive training period) more than runners with low baseline HRV.”  This result makes intuitive sense too: better HRV reflects greater readiness to train, which indicates a body more adaptable to higher level training.  If your dish is already cooked, keeping it in the oven will not yield a favorable result.  HRV gives the status of our training “dish” so we know how much longer to cook. 

Conclusion

These are only three studies, but they make some key points for HRV use.  First, HRV can be used as a guide for daily training decisions to optimize what training is best TODAY.  Second, HRV tracks alongside decrements in general health.  Finally, a higher HRV may reflect a great ability to adapt to harder training.  Though more study is warranted to confirm these results within specific endurance events and to further refine how we understand magnitude of HRV changes, there is sound evidence that HRV measures what it is purported to measure.  As such, it is a potentially valuable tool to guide training decisions daily, weekly, and seasonally. 

References

Plews DJ, Laursen PB, Kilding AE, Buchheit M.  Heart rate variability in elite triathletes, is variation in variability the key to effective training? A case comparison.  Eur J Appl Physiol. 2012 Nov;112(11):3729-41. doi: 10.1007/s00421-012-2354-4. Epub 2012 Feb 25.

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

Vesterinen V, Häkkinen K, Hynynen E, Mikkola J, Hokka L, Nummela A.  Heart rate variability in prediction of individual adaptation to endurance training in recreational endurance runners.  Scand J Med Sci Sports. 2011 Aug 3. doi: 10.1111/j.1600-0838.2011.01365.x. [Epub ahead of print]

Berkoff, DJ et al Heart Rate Variability in Elite American Track and Field Athletes. Journal of Strength and Conditioning Research. 2007 Feb;21(1):227-31.

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