The Bulgarian Split Squat (BSS) is a unilateral exercise that targets one leg at a time by elevating the rear foot on a stable surface. This single-leg training method is used to develop lower body strength, improve balance, and correct strength discrepancies between the left and right sides of the body. The BSS is a modified lunge that isolates the work to the front leg, placing a significant load on the musculature of the hip and thigh.
The Primary Force Generators
The forward leg bears the majority of the body’s weight and is responsible for the powerful movements of knee and hip extension that drive the body upward. The quadriceps femoris, the four muscles on the front of the thigh, serve as primary movers by executing knee extension. The vastus lateralis, vastus medialis, and vastus intermedius work intensely to straighten the knee joint against resistance during the ascent phase.
The rectus femoris, the fourth quadriceps muscle, is unique because it crosses both the hip and knee joints, contributing to both knee extension and hip flexion. A deep descent places a significant stretch on the quads, which contributes to high muscle activation. This high degree of knee flexion, where the knee travels forward, dictates the intense recruitment of the quadriceps.
The gluteal muscles are powerful contributors, especially the gluteus maximus, which drives hip extension. This action pulls the torso and femur back into an upright position from the deep, flexed bottom position. The substantial range of motion at the hip joint ensures heavy recruitment of the glutes. The gluteus medius, located on the side of the hip, stabilizes the pelvis and prevents the working knee from collapsing inward during the lowering phase.
Supporting and Stabilizing Musculature
While the quads and glutes provide the primary lifting force, supporting muscles are actively engaged to maintain posture and control. The hamstrings, situated on the back of the thigh, assist the gluteus maximus in performing hip extension, particularly when driving upward from the deepest point. This group, which includes the biceps femoris and semitendinosus, also acts as a dynamic stabilizer at the knee joint.
The adductor magnus, a large muscle of the inner thigh, also contributes significantly to hip extension, working with the glutes and hamstrings. Adductor muscles are also responsible for maintaining proper alignment of the working leg, preventing the knee from drifting laterally or medially.
The unilateral stance places considerable demand on the core musculature to prevent unwanted shifting or rotation of the torso. The erector spinae, running along the spine, maintain an upright torso position. Abdominal muscles, including the obliques, brace the trunk against lateral sway, stabilizing the center of gravity challenged by the single point of contact.
The calf muscles of the working leg, specifically the gastrocnemius and soleus, are engaged to ensure foot stability and maintain ankle rigidity. The small muscles of the foot and ankle stabilizers also fire continuously to prevent excessive pronation or supination. This coordination trains lower body strength alongside balance and proprioception.
Adjusting Foot Placement for Targeted Activation
The emphasis placed on the quadriceps or gluteal muscles can be manipulated by altering the position of the front foot and the angle of the torso.
Glute-Dominant Variation
To maximize glute activation, use a wider stance where the front foot is placed further from the rear bench. This allows for a greater forward torso lean during the descent, increasing the load on the gluteus maximus and hamstrings during hip extension. This modification ensures the hip joint is the primary focus of the lifting phase.
Quad-Dominant Variation
To place greater stress on the quadriceps, position the front foot closer to the elevated rear foot, creating a narrower stance. Maintaining a more vertical torso is necessary for this variation. This vertical orientation increases the range of motion and load at the knee joint.
Allowing the knee to travel significantly forward over the toes maximizes knee flexion, directly increasing the workload on the quadriceps. This adjustment changes the exercise profile from a hip-dominant push to a knee-dominant push, making the BSS adaptable for targeting specific lower body muscles.