Biological aspects and self-evaluation of shiftwork adaptation.

Two male truck drivers working in a Brazilian cellulose plant and classifying themselves as "well-" and "ill-adapted" to a shiftwork schedule of 4 days-on and 1 day-off, participated in an autorhythmometric study. Psychophysiological self-ratings (calmness, stress and alertness), oral temperature measurements and urine collections (detection of K+,Na+ and 17-OH concentrations) were performed regularly during the waking period for 15 consecutive days during the shift schedule--the midday shift (11:00 to 19:00 h), early-morning shift (03:00 to 11:00 h) and evening shift (18:00 to 02:00 h), including days-off. Cosine fitting of the data to a successive running one-day window revealed different individual temporal patterns, with the "well-adapted" subject showing a relatively stable phase relationship of the variables under study and the "ill-adapted" subject showing a less stable relationship. The different patterns could explain, at least partially, the fact that one subject feels "adapted" to shiftwork and the other not.