Effect of time of day on height loss response variability in asymptomatic participants on two consecutive days

Ergonomists measure height loss in relation to loads imposed on the spine. It is difficult to interpret whether height loss responses recorded on different days are accurate due to natural daily fluctuations in height loss and measurement variability. The objective of this research was to investigate whether the variability of height loss in the sitting position is affected by time of day and to analyse day-to-day variability in asymptomatic participants. Fifty asymptomatic participants attended two sessions (morning and afternoon) of stadiometry testing on four separate days. The results showed that a variability of height loss response changes in excess of 0.886 mm in morning and 1.128 mm in afternoon between days indicates that an intervention itself has influenced height loss. Future investigations on height loss in sitting should take these results into consideration to confidently state that an intervention has influenced height loss response at each time of day. Practitioner summary: Daily fluctuation creates difficulties when interpreting whether height losses recorded on different days and times are intervention related. Seated stadiometry measures on different days and times of day demonstrated specific levels of natural variation. Changes above 0.886 mm (morning) and 1.128 mm (afternoon) can be attributed to intervention effects. Abbreviations: LBP: low back pain; SEM: standard error of measurement; MeanSDs: means of standard deviations.