Brief report Stadiometry: on measurement technique to reduce variability in spine shrinkage measurement J. Peter Stothart a , Stuart M. McGill b, * a School of Human Kinetics, University of Ottawa, Ottawa, Ont., Canada b Occupational Biomechanics Laboratory, Department of Kinesiology, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 Received 4 June 1999; accepted 23 December 1999 Abstract Objective. To test the eect of two measurement techniques for repeated measures of spine height using stadiometry following ®ve experimental activity conditions. Design. Six subjects were repeatedly measured while they stepped in and out of the stadiometer for each pair of measures and again on another day when they remained in place in the stadiometer for all 10 measures. Results. There was much greater variability in height measures with the ``in±out'' method while the ``in place'' method dem- onstrated a steady shrinkage over the 3±3.5 min required to obtain the repeated measures. Relevance Contrary to popular practice, leaving a subject in the stadiometer during repeated measures includes the shrinkage that occurs over the 3±3.5 min of measurement when standing and reduces random variation due to posture change. Ó 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction Eklund and Corlett [1] showed that changes in body height can be used as a measure of vertebral disc com- pression to re¯ect spinal loading, which when excessive, can lead to low back injury. This approach grew out of the need for a straightforward, inexpensive technique to evaluate cumulative loading eects on the spine for various work tasks and postures. The method of Eklund and Corlett utilizes a device called a stadiometer which is an upright structured frame designed to control pos- ture and adapt very speci®cally to any subjectÕs surface contours to consistently maintain posture over a number of stature measurement trials. While the device is inex- pensive and noninvasive, and designed for precise measurement, precision is only achieved with consider- ation of intrasubject and intersubject variability of bio- logical sources together with variance from the measurement technique. The link between spine shrinkage and spine loading history is not straightforward. We have known for well over a century that people are taller in the morning, shrink progressively through the day and recover their height overnight while sleeping. In fact, in 1935, DeP- ukey [2] reported that the average daily height loss for his sample of 1216 subjects (age: 5±90 years) was 15.7 mm, or about 1% of body height. At the same time, as we have been aware of circadian variations in stature, in vitro research has shown that the intervertebral discs experience a slow and continuous deformation under conditions of mechanical load. Kazarian [3] demon- strated that this deformation or ÔcreepÕ occurred as a time-dependent function of load. Recovery follows similar conventional viscoelastic behaviour. Foreman and Linge [4] have concluded that heel pad thickness (following at least 5 min of unweighting) may be a confounding factor for measuring height and they sug- gest waiting for a period of 2 min for the heel pad shrinkage to reach equilibrium. While several research- ers have made attempts to ®ne tune the measurement methodology and employ more sophisticated instru- mentation to reduce variability in spine length, no re- searchers have systematically examined the sources of Clinical Biomechanics 15 (2000) 546±548 www.elsevier.com/locate/clinbiomech * Corresponding author. E-mail address: mcgill@healthy.uwaterloo.ca (S.M. McGill). 0268-0033/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 8 - 0 0 3 3 ( 0 0 ) 0 0 0 0 3 - 6