Power-Based Threshold Testing: Why Heart Rate Can Mislead Your Training

Step tests on a ski treadmill (rullband) are a popular and valuable method for determining an athlete’s lactate threshold. However, it’s important to understand how to correctly interpret the results. The common approach is to use measured blood lactate and heart rate (pulse) to define heart-rate zones and threshold values. But depending on how quickly an athlete’s heart rate responds, this rapid interpretation can be misleading.

Why Heart Rate Responds Too Slowly

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

In the graph, you can clearly see that from the second stage onward, heart rate continues to rise throughout the entire workload. This makes it extremely difficult to pinpoint the exact heart rate that corresponds to the measured lactate level at each stage. Based on lactate and the Borg scale, the threshold occurs during the third stage, and in terms of power output, the 4 mmol lactate threshold falls somewhere between stage two and stage three. By interpolation, the threshold power is approximately 200 watts, with an estimated threshold pulse of about 152 bpm.

Why Power Is a More Reliable Threshold Metric

The test athlete’s own experience confirms that the threshold power aligns well with the intensity they typically hold during intervals—while the estimated heart-rate threshold is clearly too low. This example highlights why tracking power is crucial in training, and why you cannot reliably control high-intensity intervals (above threshold) based on heart rate alone.

Key Takeaway for Skiers

Heart-rate–based threshold testing is reactive. Power-based threshold testing is precise, immediate, and directly tied to performance. For cross-country skiers, roller skiers, and endurance athletes aiming for accurate pacing, smarter intervals, and measurable progress, power is the gold standard.