Activation of the deep lumbar multifidus during common rehabilitation and resistance exercises

The purpose of this investigation was to determine the effect of common trunk exercises (bird-dog, back extension, glute bridge, and reverse hyperextension), loading, (unloaded and 10% bodyweight), and exercise phases (concentric, isometric, eccentric) on deep lumbar multifidus (DLM) activation. Repeated measures analyses of variance were used to compare DLM amplitude and relative contribution between exercises, loads, and phases. Multifidus activation from 34 healthy adults was collected with indwelling electrodes and normalized to a maximum voluntary isometric contraction (MVIC). DLM activation was greater during the reverse hyperextension compared to bird-dog (+13.5% MVIC), glute bridge (+14.3% MVIC), and trunk extension (+5.3% MVIC). A 10% bodyweight load resulted in a negligible DLM activation increase (+3.8% MVIC) across all exercises. Relative DLM contribution was greater during the bird-dog compared to all other exercises (range: 12.2 to 14.5%). Relative contribution was greater in unloaded exercises compared to loaded (0.9%), and greatest during the isometric and concentric phases (range: 16.3% to 19.4% versus eccentric). The greatest activation of the DLM occurs during large trunk extension-based exercises, but the bird-dog best activates the DLM with minimal synergistic activation (superficial multifidus and erector spinae).