Spinal shrinkage in females: circadian variation and the effects of circuit weight-training

Publisher Website
Google Scholar
Abstract
Compressive loading of the spine leads to spinal shrinkage and a loss of stature. The aim of this study was to measure the circadian variation in the stature of females and to examine differential effects of spinal loading with the time of day. Ten females aged 20-30 years were studied in nine measurements on a 24-hour period. Between rising and retiring to bed, the mean peak-to-trough variation was 15.4 mm (0.92% of stature). Subjects underwent two sequences of 20 min circuit-training with weights, followed by 20 min reclining in Fowler''s position and 20 min standing erect, these being first thing in the morning after 7 hours of sleep and before retiring at midnight. Mean loss of height from circuit-training was 5.4 mm in the morning and 4.3 mm in the evening (P < 0.001): mean height regained in Fowler''s position was 4.5 mm and 3.4 mm respectively (P < 0.05). There were significant height losses in the subsequent standing posture but no time of day effect. Height losses with exercise were related to the isometric strength of the back muscles and to the perceived exertion. Results support the hypothesis that height losses from a given spinal load will be of smaller anplitude when body height is in the trough of circadian variation.