Impact of training-shift change on chronotype and social jetlag: a longitudinal study on dancers

ABSTRACT Variations in circadian phase are expected after extreme changes of regular schedules. We took advantage of a real-life model of dance students to address the influence of social pressures on chronotype and sleep patterns in a paired longitudinal study. Seventeen dancers (18–27 years old) being trained at the Uruguayan national dance school ENFA-SODRE switched from training in the night shift in 2019 to the morning shift in 2021 and were evaluated using the Munich Chronotype Questionnaire. Dancers showed a significant advance in their chronotype (07:08 ± 01:39 to 05:12 ± 00:56, p = 0.043) and a significant increase in social jetlag (1.71 ± 1.05 to 2.46 ± 0.80, p = 0.027), while sleep duration fell within the recommended range for the age in both the night shift and the morning shift. The change in chronotype is correlated with the change in social disruption (n = 12, p = 0.038, R2 = 0.36). Dancers alternately used the strategy of oversleeping on free days (associated with higher SJL) or advancing their chronotype (with slight or no change in SJL). Analyzing the effects at the individual level, we were able to highlight the plasticity of the circadian system to cope with the impact of the morning training schedule within non-sedentary late young adults who abruptly, but permanently, changed the timing of their dance training.