Table 2 The description of variables of stress and recovery based on firstbeat analysis server

Stress variables For non-exercise data segments, continuous indices of stress are used to identify the time when the body is in a stress state. Stress state is defined as an increased activation in the body when sympathetic nervous system activity is dominating and parasympathetic activation is decreased. Stress can be induced by external and internal stress factors, and the definition of the stress state does not take into account the nature of the stress response, i.e., whether it is positive or negative.

Work stress

The percentage of stress time during working hours

Total stress

The percentage of stress time in a workday (including leisure time and night)

Stress index

Absolute value characterizing the magnitude of stress processes on a workday (including leisure time and night)

Recovery variables, 24 hours Continuous indices of recovery are used to identify the time when the body is in a recovery state. Recovery state is defined as a decreased activation in the body during recovery, rest, and/or peaceful working. This state is related to the lack of external and internal stress factors, and parasympathetic activation is dominating.

Total recovery

The percentage of recovery time in a workday (including leisure time and night)

Recovery index

Absolute value characterizing the magnitude of recovery processes in a workday (including leisure time and night)

Recovery variables, sleep time

RMSSD

Average of the RMSSD (root mean square of successive differences) vector values during sleep periods. High RMSSD values are associated with increased parasympathetic activity and good recovery while low values during rest indicate poor recovery. The RMSSD value should be over 20 during sleep in a normal situation.

Stress balance

Indicates proportion of time of stress and recovery reactions during sleep periods in the measurement period; the used values are from −1 to 1. Values from 0.5 to 1 indicate good recovery; values from 0 to 0.5 indicate moderate recovery; and values from 0 to −1 indicate weak recovery.

Recovery index

The recovery index gives an estimate of a person’s recovery during sleep time. The 4-h window for determining the recovery index is set to start 30 min after going to bed. The index summarizes several factors, including RMSSD and other HRV variables, and takes into account the other functions of ANS while determining the value for the index.