1 Department of Health, Kinesiology and Applied Physiology, Concordia University, Montreal, QC, Canada.
2 School of Rehabilitation Science, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada.
3 Faculty of Medicine and Health, School of Health Sciences, The Kolling Institute, University of Sydney, Sydney, NSW, Australia.
4 Northern Sydney Local Health District, The Kolling Institute, St Leonards, NSW, Australia.
5 School of Health, Concordia University, Montreal, QC, Canada.
6 Department of Orthopedic Surgery, McGill University Health Centre, Montreal, QC, Canada.

Study DesignProspective Randomized Controlled Trial.ObjectivesTo investigate the effect of combined motor control and isolated lumbar strengthening exercise (MC + ILEX) vs general exercise (GE) on upper lumbar paraspinal muscle volume and composition, strength and patient outcomes in individuals with chronic low back pain (LBP).Methods50 participants with nonspecific chronic LBP were randomly allocated (1:1) to each group (MC + ILEX or GE) and underwent a 12-week supervised intervention program 2 times per week. Magnetic resonance imaging was performed at baseline, 6-weeks and 12-weeks to examine the impact of each intervention on multifidus (MF) and erector spinae (ES) muscle volume (cm³) and fatty infiltration (%FI) at L1-L2, L2-L3 and L3-L4.ResultsOur results revealed no significant between-groups findings for MF and ES %FI and volume, and patient-reported psychosocial measures. However, both groups had significant within-groups decreases in MF %FI at L1-L2, L2-L3 and L3-L4, with concomitant decreases in MF volume at L1-L2 and L2-L3, and at L3-L4 in the GE group. Each group displayed significant improvements in Kinesiophobia, while only MC + ILEX had significant improvements in pain catastrophizing, anxiety, depression and sleep. Lastly, significant correlations were found between change in Kinesiophobia and upper lumbar MF %FI, and between change in strength and lower lumbar MF and ES size.ConclusionsBoth exercise interventions may help reduce upper lumbar MF %FI in individuals with chronic LBP, while MC + ILEX could significantly improve important patient outcomes. Our results support the idea that improvements in paraspinal muscle health associate with better patient outcomes. Further high-quality imaging studies are needed to explore these relationships.