  Quantifying lumbar back motion during functional activities in real-life
environments may contribute to a better understanding of common pathologies
such as spinal disorders. The current study therefore aimed at the comparative
evaluation of the Epionics SPINE system, a portable device for measuring
sagittal lumbar back motion during functional activities. Twenty healthy
participants were therefore evaluated with the Epionics SPINE and a Vicon
motion capture system in two identical separate research visits. They performed
the following activities: standing, sitting, chair rising, box lifting,
walking, running and a counter movement jump (CMJ). Lumbar lordosis angles were
extracted as continuous values as well as average and range of motion (ROM)
parameters. Agreement between the systems was evaluated using Bland-Altman
analyses, whereas within- and between-session reliability were assessed using
intraclass correlation coefficients (ICC) and minimal detectable changes (MDC).
The analysis showed excellent agreement between the systems for chair rising,
box lifting and CMJ with a systematic underestimation of lumbar lordosis angles
during walking and running. Reliability was moderate to high for all continuous
and discrete parameters (ICC>=0.62), except for ROM during running (ICC=0.29).
MDC values were generally below 15{\deg}, except for CMJ (peak values up to
20{\deg} within and 25{\deg} between the sessions). The Epionics SPINE system
performed similarly to a Vicon motion capture system for measuring lumbar
lordosis angles during functional activities and showed high consistency within
and between measurement sessions. These findings can serve researchers and
clinicians as a bench mark for future investigations using the system in
populations with spinal pathologies.
