Research: Heart Rate Deflection Point

Below is an article I wrote over a year ago (which makes the pre-publication reference seem a bit odd). However, this is a useful departure point for some future articles on Conconi testing and others.

Alternative to Bloodletting, Facemasks and Hoses
Many training prescriptions are based on specific measurements like VO2Max or lactate threshold. To obtain these measurements often requires costly lab-tests with masks and tubes and frequent blood-letting. Researchers, coaches and athletes would presumably all prefer less-invasive, simple and affordable alternatives to VO2Max and blood lactate type testing.

One alternative is the heart rate deflection point (HRDP). The notion behind HDRP is that heart rate allegedly increases linearly with intensity until a certain point, the HRDP. To ascertain HRDP, all a rower needs is a heart rate monitor, an ergometer and an assistant to write down their pulse at a certain power (watts). Plotting the results on a graph is easy enough and may reveal the HRDP, which apparently is a significant "flattening"of the heart rate relative to the otherwise upward sloping line. Here is an example, where the red dots represent the coordinates of pulse and watts. The black line is an Excel-generated "trend line" which makes it easier to see a deflection point.

Recently, I received a pre-publication abstract of research (J Strength Cond Res. 2009 Dec 24.) suggesting a "strong relationship between heart rate deflection point (HRDP) and ventilatory threshold (VT) in trained rowers."

Ventilatory threshold (VT) is a term that applies to breathing rate. As exercise intensity increases, the breathing rate tends to increase in a predictable linear fashion, up to a certain point--ventilatory threshold--after which it accelerates. Below is a depiction of VT from a company that makes a ventilatory threshold detector. The blue line represents breathing rate (ventilation), the grey line represents the linearity of the increase in breathing rate with an increase in power (watts). The red line is heart rate and VT represents the ventilatory threshold, the point where the respiration rate rapidly increases.

Ventilatory Threshold is Roughly Equivalent to Lactate Threshold
Ventilatory threshold is associated with a rise in blood and muscle acidosis; many physiologists (example) believe ventilatory threshold and lactate threshold are closely related or parts of the same cascade of physiological changes that occur at this exercise intensity. The McArdle, Katch and Katch physiology text book states: "lactate threshold...occurs at the point...of ventilatory threshold." [Those two ellipses suggest I took some liberties with this quote, but I really didn't.]

The J Strength Cond Res. 2009 Dec 24 study of 89 rowers is interesting because the researchers analyzed breathing rates and heart rates and found the deflection point and ventilatory thresholds occurred in a predictable and useful fashion, so that one could use HDRP as a reasonable proxy for ventilatory threshold. The researchers conclude that: "trained rowers may be able to periodically assess their aerobic endurance and evaluate the effects of training programs using the HRDP method."

This suggests, by transitive property of equality, that HRDP is roughly equivalent to Lactate Threshold (if HRDP ≈ VT and VT ≈ LT, then HRDP ≈ LT)

There seems to be some cross-sport corroboration of this phenomenon (HDRP being roughly equivalent to ventilatory threshold). This study of cross country skiers and this study of cyclists found similar results: heart rate deflection point and ventilatory threshold are highly related.

On the other hand, this study of runners found (oddly) that they could identify the heart rate deflection point of runners on a treadmill, but not on the track. Additionally, they concluded that "HR deflection point was not an accurate predictor of lactate threshold."

Heart rate is variable based on many environmental, physiological and psychological factors.  In J Strength Cond Res. 2009 Dec 24.,  three experts eye-balled the data to arrive at HRDP. They also used computer regression analysis, but some of this reading is very subjective.

In conclusion, Heart Rate Deflection Point will likely continue to be a frequently studied topic as it represents a non-invasive, inexpensive way to potentially serve as a proxy for ventilatory threshold and lactate threshold, which are deemed to be important physiological metrics.

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