Influence of self-reported vascular health and physical activity level on intravoxel incoherent motion imaging response to exercise in chronic low back pain

Introduction In individuals with chronic low back pain (CLBP), degenerative changes in paraspinal muscles, such as fatty infiltration and reduced vascularization, may impair muscles’ physiological response to exercise, limiting recovery potential. Intravoxel incoherent motion (IVIM) imaging enables assessment of muscle microvascular perfusion (D*) and intracellular diffusion (D) in response to exercise. Previous work demonstrated that individuals with chronic LBP exhibit attenuated IVIM responses to exercise, and that these responses predict clinical improvement following rehabilitation. Yet the mechanisms underlying these alterations remain unclear. Vascular comorbidities, frequently reported in individuals with CLBP, may impair exercise-induced vasodilation and limit microvascular perfusion in lumbar muscles, while reduced physical activity (PA) levels, also commonly observed, may contribute to alterations in muscle microstructure. This study investigated whether systemic vascular health and PA level moderate lumbar paraspinal IVIM responses to acute exercise in individuals with CLBP. Methods Seventy-nine participants with CLBP underwent lumbar IVIM imaging before and after a lumbar extension exercise. IVIM parameters D, D* and perfusion fraction (f) were measured for paraspinal muscles. Participants were classified as having a known vascular condition (n=26) or no vascular condition (n=53), and stratified into High (n=42), Moderate (n=23), or Low PA (n=14) groups based on the International Physical Activity Questionnaire. Linear mixed models examined the moderating roles of vascular health and PA on IVIM parameters, controlling for age, BMI and relative resistance as between-groups differences were observed. Results There was a significant main effect of Vascular condition on D (p=0.01), with the Vascular group having lower absolute values pre and post-exercise. There was a significant Time x Vascular interaction for D* (p=0.02): the Vascular group showed an attenuated response compared to the No vascular group. There was no main effect of PA on IVIM parameters, nor interactions with Time, except a trend for PA main effect on f (p=0.06). Discussion Vascular health moderates lumbar paraspinal intracellular diffusion and microvascular responses to acute exercise in CLBP. These findings contribute to a better understanding of the physiological significance of lumbar muscle IVIM parameters in chronic LBP.