Table 1.
Sleep and circadian-related variables.
| Chronotype | Abreviations | Definition |
|---|---|---|
| Acrophase | Time period during which the daily cycle of TAP peaks | |
| Objective chronotype | Acrophase of TAP determined by Cosinor’s analysis | |
| Subjective chronoype | MCTQ | Individual chronotype assesed by Munich Chronotype Questionnaire |
| Sleep parameters | ||
| Central sleep timing | Timing of the average of the five consecutive hours of maximum values of sleep | |
| Circadian Function Index | CFI | A numerical index that determines the circadian robustness, based on three circadian parameters: Interday Stability (IS), Intraday Variability (IV) and Relative Amplitude (RA). CFI oscillates between 0 (absence of circadian rhythmicity) and 1 (robust circadian rhythm) |
| Day–night contrast | Difference between the average of measurements for the five consecutive hours with the maximum TAP and the average of measurements made for the 10 consecutive hours with the minimum TAP divided by the sum of both values | |
| Depth of sleep | Hourly average during the 5 consecutive hours of minimum values of TAP | |
| Duration of sleep | Difference between sleep bedtime and sleep awake time | |
| Interday stability | IS | Constancy of the 24 h rhythmic pattern over days. A stable rhythm is characterized by a 24 h profile that remains very similar from day to day |
| Intraday variability | IV | Fragmentation of the rhythm. Its values oscillate between 0 when the wave is perfectly sinusoidal and 2 when the wave describes a Gaussian noise |
| Regular habits | Derived from the Interday stability (IS): determines the constancy of the 24 h rhythmic pattern over the 7 days. A stable rhythm is characterized by a 24 h profile that remains very similar from day to day | |
| Relative amplitude | RA | Difference between the maximum (or minimum) value of the cosine function and mesor |
| Social jet lag | Difference in the midpoint of sleep between weekend (MSFsc) and weekdays (MSW); (Social jet lag = MSFsc—MSW). Subjects with more than 2 h of difference in the midpoint of sleep between weekend and weekdays were identified as having social jet lag21 | |
| Midpoint of food intake | Average of the seven days of the midpoint between breakfast and dinner times (first and last eating episode) | |
| TAP algorithm | TAP | The integrated TAP variable is calculated using the following procedure: we first normalized the TAP variables by calculating the 95th and 5th percentiles for each variable. Wrist temperature values were inverted since activity and position values were opposites, so that the maximum values for all 3 variables occurred at the same time of the day. Then we calculated the mean of the 3 normalized variables, where 0 corresponded to complete rest and sleep and 1 to periods of high arousal and movement |