The Physiology of Bulgarian Split Squat: Targeting Muscles and Box Height Considerations

The Bulgarian split squat (BSS) is a powerful exercise that zeroes in on the gluteus maximus and quadriceps femoris. Notably, it enhances single-leg stability and flexibility, offering a wider range of motion compared to traditional lunges. Proper form is essential, with approximately 80% of your body weight distributed onto the front foot. To intensify gluteus maximus engagement, a slight forward lean from the hip is recommended.

Muscle Engagement and Box Height

The study delves into the impact of box height variations on specific leg muscles during the Bulgarian split squat (BSS). Muscle activity was measured through electromyography (EMG), yielding intriguing insights.

1. Muscle Activation

When using a taller box, the muscles under scrutiny exhibited slightly higher activity levels. However, this disparity did not achieve statistical significance.

2. Intensity Levels

With the taller box, the targeted muscles operated at approximately 41% of their maximum capacity (MVIC). In contrast, the shorter box resulted in activity levels of about 38% MVIC.

3. Implications of Small Difference

While a mere 3% discrepancy may not appear significant, related research suggests that increasing weight or speed during squats can amplify spinal and disc stress.

4. Body Position Influence

The positioning of your body during BSS significantly affects muscle engagement. A forward-leaning posture can augment the strain on the lower back muscles.

Box Height Recommendations

For optimal muscle engagement and injury prevention, opting for a shorter box, roughly half the height of the tibia, is advised. This choice is gentler on the lower back muscles and reduces the risk of injury.


It’s essential to acknowledge that during BSS, an anterior tilt of the trunk can lead to hyperextension of the lumbar vertebrae. This, in turn, increases spinal and intervertebral disc pressure and may lead to fatigue of the lumbar vertebral nerves. Additionally, employing a taller box, such as a bench, necessitates a greater range of motion. According to the American College of Sports Medicine (ACSM), the normal range of motion for the rectus femoris muscle exceeds 80 degrees. However, using a taller box may push the knees beyond this limit, potentially posing a challenge to the knee joint and increasing the risk of injury.

rectus femoris

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In summary, understanding the physiological aspects of BSS and selecting the appropriate box height are crucial for optimizing the benefits of this exercise while minimizing the risk of injury. Always prioritize proper form and consult with a fitness professional if you have any concerns about your workout routine.

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