Some authors pointed out the influence of some psychophysiological circadian factors. Subjects having a greater amplitude of the oral temperature circadian rhythms seem to tolerate nightwork better, while it is the opposite for those with internal
desynchronization ; on the other hand, ‘evening types’ show fewer sleeping problems and a better tolerance than ‘morning types’ . Other authors have stressed the negative influence of some personality and behavioural aspects, such as introversion
and neuroticism , or rigidity of sleeping habits