The six classic determinants of gait

The six classic determinants of gait are biomechanical features that optimize walking efficiency by minimizing the vertical and lateral displacement of the body’s center of gravity (COG) during locomotion. These determinants were first described by Saunders, Inman, and Eberhart in a 1953 seminal paper and represent movements and physiological strategies that contribute to a smooth, energy-efficient gait pattern. Essentially, the six determinants collectively reduce excessive motion that would otherwise increase energy expenditure and produce an awkward walking style sometimes described as a “compass gait,” where the legs move as rigid levers without the subtle joint actions that modulate motion.

The six determinants of gait are:

1. Pelvic Rotation
   The pelvis rotates approximately 4 degrees forward on the side of the swinging leg and 4 degrees backward on the stance leg, totaling about 8 degrees of rotation in the transverse plane during walking. This rotation lengthens the stride and reduces the rise and fall of the body’s center of gravity by about 9.5 mm. Without pelvic rotation, the body would have to lift the center of gravity more for each step to cover the same distance, which would increase energy demands and vertical displacement. This rotation also contributes to smoother forward progression by advancing the hip of the swinging limb faster.
2. Pelvic Tilt
   Pelvic tilt, sometimes called pelvic obliquity or pelvic listing, involves a slight drop of the pelvis on the side opposite to the stance leg during the stance phase. This lateral tilt decreases the height that the center of gravity must rise, thereby reducing vertical displacement and energy costs. The tilt lessens the vertical excursion by about an inch per stride, contributing to a more fluid gait pattern. Pelvic tilt also assists in maintaining balance by controlling side-to-side motion, ensuring the body’s weight is positioned over the supporting foot.
3. Knee Flexion in Stance Phase
   After the heel strike (initial contact), the knee flexes slightly (about 15-20 degrees) to absorb shock and further lower the center of gravity during midstance. This knee flexion acts as a natural shock absorber, allowing the body to better handle ground reaction forces while smoothing the vertical trajectory of the center of mass. Without this knee flexion, the rise of the center of gravity would be more abrupt, causing a less efficient and more jarring gait.
4. Foot and Ankle Mechanism
   The foot and ankle work together to modulate the vertical center of gravity. At heel strike, the ankle is dorsiflexed, and the center of rotation is elevated. As the foot moves toward flat on the ground, the ankle plantarflexes, lowering the center of rotation and allowing the body to descend smoothly. During push-off, the heel lifts, and the ankle plantarflexes again, raising the center of rotation and propelling the body forward. This complex motion helps minimize abrupt changes in vertical motion, enhances shock absorption, and contributes to smooth forward progression by acting like a rocker system
5. Knee Motion in the Swing Phase
   The knee flexes during the swing phase to shorten the leg, allowing it to clear the ground more easily and reducing the upward displacement of the center of gravity. The knee then extends to prepare for the next heel strike. This mechanism allows for a smoother, more controlled leg swing and contributes to energy efficiency by preventing the body from moving up and down excessively. The swinging knee acts as a lever that helps conserve momentum while conserving energy
6. Lateral Displacement of the Pelvis
   There is a controlled side-to-side shift of the pelvis over the stance leg to maintain balance and ensure the center of gravity remains within the base of support. This lateral pelvic displacement is necessary for stability, preventing the body from falling over the unsupported limb. The amount of sway is minimized by normal knee valgus and base of support width. This lateral shift not only aids in balance, but also reduces the amount of muscular effort needed to stabilize the body during single-limb support phases of gait.

Significance and Clinical Relevance

These six determinants present an integrated approach by which the body ensures walking is energy efficient, stable, and fluid. By minimizing the vertical and lateral displacement of the center of mass, the body reduces wasted energy that would otherwise be used to counteract excessive motion. The determinants provide a framework for clinicians to assess gait abnormalities and design interventions for pathological conditions that disrupt normal gait mechanics.

For example, a reduction in pelvic tilt or rotation due to weakness or stiffness may increase vertical displacement, causing a more tiring gait pattern. Impairments in knee flexion during stance can lead to a stiff-legged gait, increasing shock to joints and reducing walking efficiency. Similarly, disruptions in foot and ankle mechanisms, such as limited dorsiflexion or plantarflexion, can alter normal center of gravity modulation and lead to compensatory movements.

Understanding these determinants also allows clinicians and rehabilitation specialists to focus on restoring specific joint motions to improve gait quality, thereby reducing fatigue, enhancing balance, and preventing secondary musculoskeletal complications.

The six determinants of gait—pelvic rotation, pelvic tilt, knee flexion during stance, foot and ankle motion, knee motion during swing, and lateral pelvic displacement—collaboratively act to minimize vertical and lateral displacement of the center of gravity. This system reduces energy expenditure, increases walking smoothness, and maintains balance during gait. By orchestrating these movements, the human body achieves efficient locomotion and a graceful walking pattern. These principles continue to be foundational in gait analysis and rehabilitation, highlighting their enduring clinical and biomechanical importance.