How does the method identify stress, recovery and physical activity?

Determination of stress and recovery state is affected by heart rate level, breathing frequency, heart rate variability and oxygen uptake. The person’s background information determines the individual levels of each state. When oxygen uptake increases to over 20% of the person’s maximal capacity (VO2max), the analysis starts to identify different levels of physical activity and no longer determines whether the state is stress or recovery. The journal markings have no effect on detection of different states.

More information about this can be found from Firstbeat's website here.