SLEEP BEHAVIOUR, ACTIVITY CIRCADIAN RHYTHM AND PSYCHOPHYSIOLOGICAL RESPONSES TO PHYSICAL ACTIVITY: THE CHRONOTYPE EFFECT.

In the past, several studies investigated the circadian rhythm of different physiological variables associated to sport, the time-of-day effects on physical performance and the reciprocal relationship between sleep and physical activity but there is a scarce literature on how the chronotype could influence all these aspects. Therefore, the purposes of this Ph.D. thesis are: 1) to assess, with the use of actigraphy, the relationship between the three chronotypes and the circadian rhythm of activity levels and to determine whether sleep parameters respond differently with respect to the time (weekdays versus the weekend) in M-types, N-types and E-types; 2) to evaluate whether a linear regression formula using the MEQ score would predict the actigraphy-based acrophase in a young Italian population; 3) to investigate the effects of chronotype on psychophysiological responses (RPE, HR and walking time) to a submaximal self-paced walking task performed in two different times of day (08:30-09:00 vs 15:30-16:30). The results showed that: 1) the acrophases of the activity levels were significantly different in M- (14:32h), N- (15:42h) and E-types (16:53h) (p<0.001) while MESOR and amplitude were similar among chronotypes; there was also a significant interaction between the chronotype and sleep parameters: Sleep Efficiency of the E-types was poorer than that of the M- and N-types during weekdays (77.9% ± 7.0 versus 84.1% ± 4.9 and 84.1% ± 5.2) (p=0.005) but was similar to that measured in the M- and N-types during the weekend. 2) There was a significant linear relationship between MEQ and the Acrophase thus, enabling us to use the equation of the regression line to obtain predictions. The predictive equation resulted as follows: 1238.7-5.487*MEQ. The precision of the estimates was excellent and the r2 was 0.70, indicating that 70% of the variance in the acrophase was explained by MEQ. 3) It was found a significant interaction between chronotype and time of day. The post hoc analysis showed a significant difference for RPE in the morning session, with E-types reporting higher RPE compared with the M-types (14.33 ± 2.45 vs 12.00 ± 1.66) (p<0.01). This Ph.D. thesis highlights two key findings: 1) the chronotype influence the activity circadian rhythm and the sleep parameters suggesting that E-types accumulate a sleep deficit during weekdays, due to social and academic commitments and that they recover from this deficit during “free days” on the weekend; 2) the chronotype and the time of day when a physical task in undertaken can influence the RPE response.