Nocturnal Lumbopelvic Mechanics and Non-Specific Low Back Pain: A Tissue-Specific, Duration-Dependent Framework.

Non-specific low back pain (NSLBP) remains the leading cause of disability worldwide, yet prevailing etiologic models incompletely account for time-dependent mechanical exposure during sleep. Existing frameworks emphasize structural, psychosocial, and neurophysiological contributors, while sleep disturbance is primarily interpreted through central or systemic mechanisms. An underrecognized gap remains: the mechanical environment of the lumbar spine and pelvis during sleep. Sleep is the longest continuous loading interval in the human spinal loading cycle, occurring under conditions of reduced active stabilization and reliance on passive tissues. Recurrent nocturnal exposure to sustained lumbopelvic alignment may influence passive tissue mechanics, afferent signaling, and motor control. From a mechanobiological standpoint, the relevant exposure is not peak load alone, but the time-integrated load on spinal tissues. Accordingly, even low-magnitude forces may become biologically meaningful when sustained over extended durations. This framework defines a conservative, hypothesis-generating exposure-response pathway linking nocturnal mechanical loading to morning symptom expression. By reframing sleep as a duration-dependent biomechanical exposure rather than a passive recovery state, it extends the temporal scope of spinal loading and establishes a previously undercharacterized, potentially modifiable domain of exposure.