Advantages
No Blood Draw, No Stress:
- Monitor OBLA in real time and continuously without interrupting exercise to draw blood. Accurately determine sustainable threshold speed and power.
No Need for Expensive Testing Equipment:
- Quantitatively track daily training effects (improved endurance) without using exhaled gas analyzers costing millions.
Compatible with All Sports:
- Because the analysis method is less susceptible to artifacts (breathing effects), it can be applied to all sports—not just running and cycling, but also aquatic exercises.
Background and Technology
For endurance athletes, the intensity at which lactic acid begins to accumulate rapidly (blood lactate concentration of 4 mmol/L, OBLA) is the most critical indicator of performance. However, accurate measurement of this requires invasive blood sampling during exercise or large-scale breath gas analyzers, making continuous monitoring during training difficult.
In principle, an increase in exercise intensity is clearly reflected in the balance of the autonomic nervous system; as the workload increases, the activity of the sympathetic nervous system—which raises heart rate—becomes more pronounced. If these physiological changes can be captured in real time, non-invasive assessment of exercise intensity becomes possible. To date, heart rate variability (HRV) analysis has been attempted as a simple measurement method; however, since there is no indicator that directly represents sympathetic nervous system activity, the ratio of low-frequency (LF) to high-frequency (HF) components (LF/HF) has generally been used as a proxy. However, it has been pointed out that LF/HF is susceptible to the effects of breathing and posture and does not necessarily accurately reflect sympathetic nervous system activity.
The inventors focused on “HR/LF,” a proprietary indicator representing the ratio of heart rate (HR) to LF. We discovered that as exercise intensity increases, this indicator exhibits a two-stage rise, and that the second stage of this rise (the inflection point) is perfectly synchronized with the point at which blood lactate concentration reaches 4 mmol/L (OBLA). This is because it accurately captures the physiological point at which sympathetic nerve activity surges, overcoming the inhibitory effects of the baroreceptor reflex. This makes it possible to identify OBLA using only heart rate data, dramatically reducing measurement costs to approximately 1/100 to 1/1,000 of the conventional cost. From this identified OBLA point, it is possible to estimate the lactate threshold or maximum oxygen uptake with high precision. In the future, by implementing this technology in wearable devices, it is expected to be utilized in all kinds of environments, whether on land or in water.
Data
- In an exercise stress test involving 29 participants, the inflection point load indicated by HR/LF (175±27 W) was statistically significantly consistent with the measured OBLA load (176±33 W).
- In the same test, the oxygen consumption calculated from the inflection point of HR/LF showed a strong positive correlation (r=0.836) with maximum oxygen consumption, the gold standard for endurance.
Expectations
Fukuoka University is seeking partner companies interested in developing mobile applications incorporating this algorithm or implementing it into existing smartwatches and sports devices.
Researchers have now completed accuracy verification using electrocardiogram (ECG) waveforms, and moving forward, they hope to collaborate on expanding its application to optical pulse sensors and conducting field tests tailored to specific sports.
It is possible to provide access to undisclosed data upon signing a CDA with Fukuoka University, and we can also arrange meetings with the PI, so please feel free to contact us.
Principal Investigator
Yoshinari Uehara, MD, PhD
(Professor, Graduate School of Sports and Health Science, Fukuoka University)
Patents and Publications
A PCT application is pending (unpublished).