Circadian variation in human stature.

The aim of this study was to monitor the creep in stature due to compression and its recovery over 24 hr in eight adult males. Measurements of stature were made at nine times during the 24-hr cycle using a purpose built metal frame tilted 5 degrees to the vertical. Accessories for standardization of posture and prevention of unwanted muscular tension included a series of microswitches on the frame, cross-beams for controlling spinal curvatures, slit spectacles used in conjunction with a mirror for proper head alignment. A dead load BAYE micrometer recorded stature to 0.01 mm. A significant circadian rhythm was established, the trough to peak variation being 19.3 mm or 1.1% of overall stature. Peak stature was measured at 0730 on awakening and the trough occurred at midnight before assuming a recumbent posture for sleep. Altogether 71% of the height gained during the night was achieved in the first half of the night's sleep. Over 50% of the height loss in a day was lost within the first hour of rising, 80% being lost within 3 hr of arising: the rate of creep decelerated throughout the remainder of the waking day. It is concluded that the rate of change in creep throughout the day varies, being greatest in the morning whilst distension is most pronounced in the early hours of sleep.