A progressive treadmill test is a popular and useful method for determining one’s lactate threshold. However, it is important to consider how to interpret the results properly. Typically, heart rate (pulse) and measured lactate levels are used to establish heart rate zones and thresholds. However, depending on how quickly an individual’s heart rate responds, one should be cautious with quick result interpretations.

The chart below shows heart rate and power output for an athlete who performed a threshold test at Sportslab last week.

In the chart, it is clear that from the second stage onward, the heart rate continues to rise throughout the stage, making it difficult to pinpoint the exact heart rate corresponding to the measured lactate level at each stage. Based on lactate values and the Borg scale (perceived exertion), the threshold occurs during the third stage. In terms of power output, the 4 mmol lactate threshold is estimated to fall somewhere between stage 2 and stage 3. After interpolation, a threshold power of approximately 200 watts and a threshold heart rate of around 152 beats per minute were obtained.

The test subject personally feels that the estimated threshold power aligns well with the power output they usually sustain during intervals, but the estimated heart rate appears too low. This example highlights why monitoring power output is crucial during training and why heart rate alone is not a reliable metric for regulating high-intensity intervals (above the threshold).