The polysomnography recording (Clínica de Sueño Dr. Estivill, Barcelona) during one normal night in the subject's usual room (in the sports hall of residence), was performed to analyse the sleep structure of each participant and to detect possible sleep pathologies that could interfere with the nocturnal rest of the subjects (Apnea/Hypoapnea, regular limb movements or parasomnia).

Cerebral activity was recorded by contact electrodes, following the techniques set by the American Academy of Sleep. Electromyographic activity (EMG) was measured by applying electrodes to the area under the chin and the tibialis anterior muscles. A body position sensor was used. The heartbeat was also recorded. Eye movements (EOG) were measured by two electrodes placed close to the eyes. Nose and mouth thermal resistances were used with a pressure transducer, as were abdominal and thoracic induction strips were used to analyse respiratory dynamics. Nasal flow and blood oxygen saturation (SaO2) were measured by pulse oxymetry. PSG data were simultaneously acquired through 15 different channels at 30s per page during 8h.

The participants’ circadian rhythms and sleep/waking cycle were studied using a multichannel Ambulatory Circadian Monitoring (ACM) device (Kronowise®, Chronolab, Murcia University) that consists of: 1) a wristwatch that includes a temperature sensor (Thermochron® iButton DS1921H, Dallas, Maxim) to record distal body temperature (°C) as an indirect indicator of sleepiness,15 and an ambient temperature sensor (Hobo® PendantTemp/Light Data Logger) (°C) and light sensor (lx); 2) an actimeter (Hobo® Pendant G Acceleration Data Logger) as a bracelet which records acceleration (m/s2) and static position (°) in three axes to evaluate repose/activity rhythms.

The sensors were worn 24h per day for 7 days, with normal everyday habits. The variables of position, activity and light were recorded every 30s and body temperature was recorded every 10min.

All data were analysed by used Circadianware® (Chronolab, Murcia University) software, and the average was shown of individual body temperature, light and activity parameters over the 7 days, and they were then compared with the standard values of a normal population.

The algorithmic calculation of body temperature (T), motor activity (A) and position (P) gave the integrated variable TAP16 as the result, this being an estimation of the level of activation which makes it possible to infer periods of sleep or wakefulness. High TAP levels correspond to low body temperatures with high values of activity and position that represent periods with a high level of mental and physical activity (wakefulness). A low TAP level corresponds to high temperature levels and low levels of activity and position, which are typical sleep values.

Analysis of the data recorded by the sensors offers a range of indicators about sleep and circadian rhythms: hours of sleep, average temperature during the night as an indicator of depth of sleep, average temperature during the day as an indicator of wakefulness or sleepiness, activity during the night as an indicator of broken sleep and depth of sleep, regular habits to evaluate circadian rhythms, the interday stability (IS) associated with the regularity of the sleep/wakefulness cycle from one day to another, the intraday variation (IV) of the recorded variables, the relative amplitude (RA) of the contrast between variables during wakefulness and sleep, and the circadian working of the wakefulness/sleep cycle (CFI) as the overall indicator of the robustness of the circadian rhythms.

The participants completed the following battery of questionnaires: the subjective level of sleepiness was measured using the Epworth sleepiness scale (ESS),17 which runs from 0 to 24 and where 9 is the value showing maximum normality. The compound morningness scale (CMS)18 measured the chronotype or genetically determined profile for eveningness or morningness which conditions the physical performance of each sportsman and sportswoman at training times. The executive functions were evaluated using the TESEN Trails Test (Test de los Senderos TESEN (JA. Portellano, R. Martínez Arias, TEA ediciones, Madrid)), a standardised questionnaire derived from the TMT,19 that is based on the capacity for visual planning. The times taken are measured together with the number of errors committed.

The profile of mood states (POMS)20 was applied to determine 7 profiles: stress, depression, anger, vitality, fatigue, confusion and sociability. This tool is widely used in sports, where it is found that negative mood states are more reduced in value than is the case in the normal population, while vitality is higher.21 This profile, which is characteristic of those who do sports, follows the Iceberg model and is affected by overtraining and fatigue.22

The polysomnographic studies detected one pathological record due to psychophysiological insomnia (case 1), one case of postural hypoapnea (case 6) and one case of excessive limb movements (myoclonus, case 12). The average values obtained in the 9 normal records are shown in Table 1: the sleep structure according to the percentages of the different phases of sleep are within normal limits, although the average total length of time slept was short, with a high level of sleep latency and an excessive number of arousals (or microwakings).

Daily recording over 7 days of the T, A, TAP, sleep and light variables supplied data on the number of hours they slept and the depth of their sleep. Their circadian rhythms of wakefulness and sleep depending on the regularity of their habits were also observed. The results were compared with those corresponding to a normal population by means of graphic representation of the weekly averages of the variables.

Fig. 1 shows an example of this type of record. The hours of sleep during different days are irregular due to poor habits. There is a high level of activity at the start of the night due to difficulty in falling asleep, and the high daytime temperature is an indication of sleepiness.

Figure 1.

(A) Diagram showing the placement of the ambulatory circadian monitoring sensors. (B) Example of graphic representation of the 7-day chronobiological study. Left: graphic representation of the weekly average of the TAP, temperature, physical activity, sleep and light variables (coloured areas), compared with the standard values for the healthy population (blue lines). Right: graphic representation of the activity (blue), position (green) and temperature (red line) variables of an individual, recorded during 7 days. The estimation of sleep duration marked by the yellow strip is characterised by high temperature, a fall in movements and a low position. Episodes of waking during sleep are characterised by movements in position and a fall in temperature.

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Table 2 shows the results of the circadian studies of all the participants together with the average of each one of the parameters that were calculated. In general it was observed that the number of hours slept during the whole week (7:35h) is less than is necessary given the participants’ age, and they sleep even less when only weekdays are considered (6:55h). This is associated with the sleepiness they suffer during the day, as detected by their generally raised temperature (daytime temperature: 33.38°C) compared with the normal value in a range of 31–33°C. Excessive activity during the night was also detected (201.09%), compared with normal values (65%–135%). This was due to broken sleep that gave rise to sleep that was not very refreshing. Finally, regularity of habits (72%) and depth of sleep (84.94%) are both lower than normal in a healthy population (75%–125% and 85%–100%, respectively). These alterations are associated with a certain degree of disruption in their circadian rhythms.

Table 3 shows other parameters which indicate the circadian functioning of the recorded variables. Low levels of the IS parameter (the regularity index) indicate that the temperature, TAP and sleep variables do not remain stable from day to day throughout the week, due to poor circadian habits. The same can be concluded from the low values of the CFI parameter, which reflects the poor circadian quality of their timetables. The high IV values show instability of the variables over 24h, indicating broken sleep. The relative amplitude (RA) of the temperature variable is low, due to the lack of difference between daytime temperature (that is abnormally high because of sleepiness) and the night-time temperature.

The length of time they sleep is completely determined by their activities and obligations during the week. We saw in Fig. 2 how they sleep for less time during the week, getting up very early to train while still going to bed late, preventing them from sleeping for as long as they need. On the other hand, at the weekend their wakefulness/sleep rhythm was generally found to become delayed, leading to a lack of synchronisation between their circadian rhythm at the weekend and during the week, a phenomenon known as social jet-lag.

Figure 2.

Graphic representation of average times slept (black bars), basketball training (light grey bars) and classes (dark grey bars), for all of the players during the week.

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The questionnaire about mood states (POMS) gave results that are comparable with the Iceberg profile that is typical of elite sportsmen and sportswomen. The results shown by the average curve for these sportswomen (Fig. 3) show excessively high stress levels, depression, confusion and fatigue, together with a fall in vitality.

Figure 3.

Graph showing the average results of the POMS questionnaire, compared with the ideal profile (Iceberg).

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The chronic sleep deficit suffered by the participants may lead to the mood instability they display, and it is also associated with a lack of physical recovery.

The average results of the questionnaire on executive functions (TESEN) were correct in terms of execution and speed, in the 85% and 90% percentiles, respectively. Nevertheless, the average score for precision, in the 30% percentile, is normal-low. This is associated with insufficient mental flexibility, excessive impulsiveness and difficulties in working memory, mixed with emotional and motivational factors.