## 1 Introduction  
A number of research studies have consistently provided evidence that low back pain is correlated with weakness and reduced endurance of lumbar extensor muscles [1; 2; 3; 4; 5; 6; 7; 8]. For these reasons, lumbar stabilization exercises are frequently prescribed in preventive and rehabilitation interventions for the lumbo-pelvic-hip complex, particularly for low back pain [9]. Additionally, lumbar stabilization exercises are used in training programs for various sports to prevent injuries and improve performance [10; 11]. Stiffening the torso, the lumbar, and other core muscles enables safer and more efficient transmission of the power generated by the lower limbs to the upper body during explosive movements [11; 12]. In these contexts, asymmetric lumbar stabilization exercises, which engage the two sides of the body differently, are routinely used alongside symmetric exercises [9; 10]. Indeed, most daily activities and sporting gestures involve asymmetric movement patterns in the upper and lower extremities. Consequently, during the execution of these tasks, the vertebral column often experiences asymmetric mechanical loadings, which are primarily engendered by load transfers among the spine, arms, pelvis, and legs. To maintain a safe neutral position of the spine in such situations, the spine-stabilizing muscles on one side of the body need to be engaged differently than those on the other side. Furthermore, asymmetries in lumbar muscle strength between the left and right sides are frequently observed and have been suggested as potential indicators of lumbar pathology [13; 14; 15]. Addressing these imbalances may require targeted corrective exercises [13; 14; 15]. Careful progressions of asymmetric lumbar stabilization exercises, appropriately dosed between the sides of the body, can gradually accustom the spinal joint structures to asymmetric stimuli. This approach can also be utilized to manage and treat imbalances in lumbar muscles between the body's two sides. Asymmetric lumbar stabilization exercises are frequently performed in prone and quadruped positions, involving lifting the upper and lower limbs in various combinations through hip extension and shoulder flexion movements. Elevating either an upper or lower limb off the ground from these body positions reduces the extension of the base of support and shifts the position of the body's center of mass. Asymmetric combinations of limb lifts further modify the base of support and its symmetry, resulting in trunk instability in the transverse and frontal planes of the body. This further challenges the lumbar stabilizers and the oblique muscles, which can reach considerable levels of activity avoiding the use of external overloads and the related mechanical loading induced on the spine's structures [16; 17]. Previous studies have recorded electromyographic (EMG) activity bilaterally from lumbar and oblique muscles during asymmetric lumbar stabilization exercises, including elevation of an upper limb and the contralateral lower limb (contralateral arm-leg rise) from the quadruped [18; 19; 20; 21; 22; 23; 24; 25; 26; 27], prone [22; 27], and plank positions [24], and elevation of a lower limb (leg rise) [18; 19; 20; 21; 26] or an upper limb (arm rise) [26] from the quadruped position. Currently, there is a lack of EMG data for isolated arm rises and leg rises from the prone position, as well as for the simultaneous rise of an upper limb and the ipsilateral lower limb (ipsilateral arm-leg rise) from the prone and quadruped positions. A recent EMG study from our laboratory analyzed lumbar multifidus and erect spine activity during the ipsilateral and contralateral arm-leg rise from the standing-prone position [28]. However, the oblique muscle activity was not recorded. Furthermore, isolated arm or leg rises from the same position were not investigated. Knowledge of all the missing information listed above would provide a more comprehensive EMG characterization and a deeper understanding of asymmetric lumbar stabilization exercises.