Advancedphysiocare

CENTRE OF GRAVITY SHIFT – THE BIOMECHANICS OF TRENDELENBURG

In normal single-leg stance, the body maintains balance by keeping the centre of gravity (COG) aligned over the base of support. The ground reaction force (R) travels upward through the stance limb, while the hip abductors—primarily the gluteus medius—generate a counteracting force to stabilize the pelvis. This creates a balanced system where torque on both sides is controlled, allowing efficient and energy-saving posture.

However, when the hip abductors are weak or unable to generate sufficient force, this balance is disrupted. The body compensates by shifting the centre of gravity laterally over the stance leg. This reduces the moment arm of body weight, effectively decreasing the torque demand on the abductors—but at the cost of altered biomechanics.

This compensatory strategy is known as the Trendelenburg pattern. Instead of the pelvis remaining level, it drops on the non-weight-bearing side. Simultaneously, the trunk leans toward the stance side to bring the COG closer to the joint axis. While this reduces muscular demand, it increases compressive forces at the hip and alters load distribution throughout the kinetic chain.

From a biomechanical perspective, this is a trade-off between stability and efficiency. By reducing the distance between the line of gravity and the hip joint, the body minimizes required abductor force. However, this increases joint reaction force and places additional stress on passive structures.

Over time, this altered alignment can lead to compensations at the knee and ankle, increased energy expenditure during gait, and a higher risk of injury. It also reflects a loss of optimal frontal plane control, which is essential for dynamic activities like walking, running, and climbing.

Ultimately, centre of gravity control is fundamental to movement. The relationship between muscle force, moment arms, and alignment determines whether the body moves efficiently or compensates under stress. Restoring hip abductor strength and proper pelvic control is key to correcting this imbalance and optimizing biomechanics.