Researchers Jamie Stanley & Jonathan Peake from the University of Queensland, with the guidance of heart rate variability (HRV) sports research supremo Martin Buchheit have put together an important review article with over 120 references. The paper takes a critical look at the research and the many studies on HRV following exercise with the objective of extracting the clearest possible recommendations on how to use HRV to maximize the effectiveness of periodised training. They focused on endurance sports because there simply aren’t enough studies on strength & power sports to come to clear conclusions yet (more studies please!).
What did they do?
They reviewed studies on HRV and exercise in two separate sections:
1) They performed detailed quantitative analysis on 8 studies that provided sufficiently complete data to analyse changes in HRV in the immediate 90 minutes following single exercise sessions at different intensities and also the subsequent 48 hour recovery period. Studies that did not include pre-exercise or baseline data were excluded. When choosing from multiple HRV parameters, they used LnRMSSD (the ithlete measure) wherever possible for reliability reasons.
The intensity level of exercise performed was categorized using a 3-zone model, (like the Lucia TRIMP) which distinguishes between exercise below first ventilatory/lactate threshold (Z1), exercise above the second ventilatory/lactate threshold (Z3) and the region between the two thresholds (Z2). The selected studies were of similar length in time however, making it difficult to categorise data on the basis of duration.
The output of the analyses was charts that showed not only the time course of HRV itself, but even more importantly, the standardised differences between pre and post exercise changes at different points in time. These effect sizes were expressed using Cohen’s d parameter, which basically makes it easy to understand the average magnitude of an effect in the presence of variations between individuals. A value close to zero represents a trivial change, a value around ±1 represents a large effect, ±2 or more a very large effect.
2) They examined studies of HRV and extreme exercise – a 46 km trail run at altitude, a 75 km x-country ski race and that hardy perennial of extreme exercise, the Ironman triathlon.
What did they find?
1) Analysing the immediate period following exercise at different intensities they found an intensity dependent effect. The highest intensity showed the slowest recovery, but in no case was HRV back to pre-exercise levels by the end of the 90 minutes. The chart below shows this short term recover for low intensity (squares), threshold (circles) and high intensity (triangles):
- This situation is mirrored for high intensity exercise, where the rebound occurs after 48 hours, following a period where HRV is depressed.
- For threshold intensity training (circles), HRV remains depressed during this 48 hour period.
2) The analysis of the extreme events revealed some additional insights:
i) HRV in the last few days before major competition was reduced, possibly because of either effects of tapering, and/or pre-event nerves.
ii) HRV returned to baseline within approximately 24 hours, suggesting that for low intensity (i.e. fully aerobic) exercise, the duration is not the determining factor for at least this aspect of recovery
What does it mean?
Linking the timing of HRV rebound to the intensity of exercise has some far reaching implications for structuring individually periodised training programs.
In particular, if the HRV rebound does really signify supercompensation (as the authors argue), then these periods are likely the optimum time to train for greatest performance gain.
The authors go on to discuss how to compose a periodised endurance programme based on these principles that we may summarise in a future post, but overall this review is an important step forward in using HRV to guide endurance training not only to avoid overtraining but to maximize performance gains.
Sports Med DOI 10.1007/s40279-013-0083-4