Effect of Forefoot-Rearfoot and Pelvic-Scapular Weight Shifts on Lower-Limb and Lumbar Muscle Activity during Static Wall-Squat Exercises

(1) Background: The static body-weight wall-squat (SBWS) exercise is often included in the early rehabilitation stages of the lower limb. To establish its effectiveness and optimise its application, it is important to precisely quantify the muscle contribution to different versions of this exercise. (2) Methods: We analysed the electromyographic activity of lower limb and lumbar muscles during the SBWS with knees flexed at 45 degrees by manipulating three different variables: horizontal distance of the ankles from the wall; scapular or pelvic location of the centre of pressure C-wall of the force exerted by the wall on the back; rearfoot or forefoot location of the centre of pressure C-GR of the ground reaction force. (3) Results: The forefoot-to-rearfoot C-GR shift significantly increased the vastus medialis, vastus lateralis, and tibialis anterior activity up to 23%, 26%, and 44% of the maximum voluntary isometric contraction (MVIC). The lumbar muscle activity was maximised (23% MVIC) shifting C-GR at the forefoot, C-wall at the scapular zone, and placing the feet far from the wall. (4) Conclusions: These SBWS methods might be effective for quadriceps, tibialis anterior, and lumbar muscles strengthening in the early phase of rehabilitation intervention as soon as the patient can tolerate partial weight-bearing. The exercise appears suitable for patients with low back pain and limited lumbar muscle endurance, or quadriceps weakness and inhibition secondary to a knee injury.