Individuals With Impaired Lumbopelvic Control Demonstrate Lumbar Multifidus Muscle Activation Deficit Using Ultrasound Imaging in Conjunction With Electrical Stimulation: A Cross-sectional Study

•Force measurements are not appropriate to investigate multifidus activation deficits.•Electrical stimulation with ultrasonography can be used to measure muscle activation.•Individuals with impaired lumbopelvic control cannot fully recruit multifidus. To determine lumbar multifidus (LM) muscle activation deficits in individuals with impaired lumbopelvic control (iLPC) based on musculoskeletal ultrasound in conjunction with electrical stimulation approach and the correlation between back extension force and LM activation. A cross-sectional study design. A university laboratory. Fifty participants (25 iLPC and 25 no low back pain [NoLBP]) were recruited from the university physical therapy clinic and surrounding areas. The musculoskeletal ultrasound was used to measure LM thickness at rest, maximum voluntary isometric contraction (MVIC), and electrical stimulation combined with MVIC, and a handheld dynamometer was used to record force during MVIC and electrical stimulation combined with MVIC. These data were used to derive LM activation (LMACT) and percentage force generation (ForceGEN). The iLPC group had significantly lower LMACT (17%) than the NoLBP group (P.05). No significant correlation was seen between LMACT and ForceGEN (P>.05). The findings support the utility of our protocol to determine LM activation deficits. The lower LM activation in iLPC group suggests that individuals with iLPC were unable to fully recruit the motor units available in LM. Force generation measurements may not be an appropriate approach to determine such deficits in LM.