This article explains step by step how to analyze the heart rate/ power relationship.

Heart rate / power chart

Rainbow line
The rainbow line tells about the sequence of your real time data. The sequence of the colors is: yellow (start), green, light blue, blue, red and purple (end). Eg.: the color code of a ride of 60 minutes: 00-10': yellow / 11-20': green / 21-30': light blue / 31-40': blue / 41-50': red / 51-60': purple.

Big squiggly line
The big squiggly line shows what your heart rate did in relation to your power-output.

Black line
The black line is the best fit line that is drawn through the big squiggly line, presenting all coordinates of the heart rate/power-speed relationship.

Slope
The slope is defined as the tangent of the angle with the best fit curve through the squigly line.

Zero position
This is the point on the heart rate/power relationship chart where the best fit black line hits the heart rate axis (y-axis).

Colour code
Colour code for training zones in the abcis (y-axis) expressed as heart rate and in the ordinate (x-axis) expressed as power.

Markers
Markers for aerobic (AT) and anaerobic threshold (ANT), if present, for the given workout or view.

Glossary of terms

Adapted power/speed
Adapted power/speed is calculated by a special algoritme on your power/speed data that takes into account the variability of power/speed data. Therefore, adaptated power is a better indicator than the average power to understand the true metabolic demands of a workout.

Load index
The Load index (LI) is a calculated number that takes into account the duration and intensity of a workout to arrive at a single score of the overall training load and physiological stress created by that workout.
One hour of functional threshold (as hard as you can go for one hour) = 60 Load index points.

Physical work capacity
PWC = power in watt at a given heart rate, named Physical Work Capacity

Slope
The slope of the black line in the heartrate power chart tells you how much your heart rate changes for each watt power-change. The more fit you are, the lower this number will be. When your aerobic capacity is better, it will take less effort to produce more watt.

Strain factor
The Strain factor (SF) is a calculated number that quantifies the intensity of a workout . It takes into account the adapted power (cycling) / adapted speed (running) of a workout in relation to your anaerobic threshold to arrive at a single score of the intensity created by that workout.
Unit: 0 - 1.3 units

Zero position
This is the point on the heart rate/power relationship chart where the best fit black line hits the heart rate axis (y-axis).
As your fitness improves, this number will decrease.