A study of 25 healthy adults found that lumbar posture during unstable sitting tasks in a laboratory setting most closely matched participants’ real-world sitting postures measured over 48 hours using wearable motion sensors.

Across the three sitting conditions—upright, preferred, and unstable—the mean lumbar flexion recorded during unstable sitting most resembled the participants’ daily postures. The mean lumbar flexion angles were 19.8° in upright sitting, 30° in preferred sitting, and about 27.1° (eyes open) to 28.1° (eyes closed) in unstable sitting. Unstable sitting showed a similar mid-range curvature to what participants exhibited during routine activities, whereas upright sitting produced less flexion.

The participants who spent more time sitting each day displayed greater seat movement during eyes-closed unstable sitting, while those who walked more demonstrated stronger coordination between lumbar movement and seat motion during eyes-open unstable sitting. The findings indicated that dynamic postural control during unstable tasks corresponded with habitual movement behavior.

“[S]pine posture adopted in a laboratory unstable sitting task is more closely related to real-world lumbar spine postures than other static laboratory-based sitting tasks,” said senior study author Paul W. Hodges, of the School of Health and Rehabilitation Sciences at The University of Queensland in Australia, and colleagues.

Researchers enrolled healthy, pain-free adults (13 women, 12 men; mean age = 30 years) who completed upright, preferred, and unstable sitting tasks under laboratory conditions followed by 48 hours of real-world monitoring.

Lumbar and thigh motion were tracked using inertial measurement units attached to the upper and lower lumbar spine and an activPAL device on the thigh to classify sitting, standing, and walking. Laboratory data were collected at 100 Hz and resampled at 20 Hz to align with the wearable recordings. Lumbar angles were expressed relative to each participant’s median standing position.

Real-world sitting postures were modeled with Gaussian mixture analysis to identify the most frequent postures for each participant. Correlations were calculated between laboratory and real-world data, adjusting for body mass index and safety-bar contact during unstable sitting.

The researchers noted that the small, healthy sample may have limited generalizability to clinical or occupational groups. The 48-hour observation period might not have captured longer-term variability in posture. The wearable sensors estimated relative rather than absolute spinal angles and were potentially influenced by soft-tissue motion. In addition, the Gaussian modeling method hasn't yet been validated for lumbar postural classification.

The researchers demonstrated that an unstable sitting paradigm can serve as a practical laboratory proxy for typical lumbar posture during daily life. By integrating motion sensors with controlled balance tasks, the study provided a reproducible approach for linking biomechanical data collected in experimental settings with free-living movement patterns. This connection between laboratory and real-world measures could establish a methodologic foundation for future studies examining posture, ergonomics, and spinal tissue loading in natural environments.

The authors reported no conflicts of interest or competing financial relationships.

Source: Journal of Clinical Medicine