Biology
Biomechanical Principles of Gait Analysis in Prosthetics
Quick fact
In the single support phase of walking, the ground reaction force can be up to 1.2 times your body weight, applying significant stress to prosthetic components and the residual limb.
Why this is interesting
Every step you take involves a complex interplay of forces and motion. But what happens to that intricate system when a limb is lost? How can engineers replicate the natural gait?
Read the full explanation
Understanding Biomechanical Principles of Gait Analysis in Prosthetics
Walking is a periodic motion we call the gait cycle. It has two main phases: stance (when the foot is on the ground) and swing (when the foot is in the air). Each phase has sub-phases like heel strike, midstance, and toe-off. Consider your own walk: you shift your weight, balance on one leg, and then move the other leg forward. Your body's center of mass moves in a smooth, undulating pattern to conserve energy. In prosthetics, we must replicate this motion for an artificial limb. The prosthetic must provide stability during stance, allow smooth swing, and generate the forces needed for push-off. It must align with the remaining joints and muscles, and match the intended activity level of the user.
A deeper explanation
The key biomechanical principle at play is Newton's third law: every action has an equal and opposite reaction. As your foot pushes on the ground, the ground pushes back—this is the ground reaction force (GRF). During walking, GRF has vertical, anterior-posterior (braking/propulsive), and medial-lateral components. The location of GRF relative to the joints creates moments (rotary forces) that flex or extend the hip, knee, and ankle. For example, at heel strike, the GRF line passes behind the knee, extending it. Muscles counter these moments to control the limb. In prosthetics, the alignment of the artificial limb—how the foot is positioned relative to the socket—affects these moments. A misaligned prosthesis can create abnormal moments that lead to discomfort, instability, or excessive loading on the residual limb. Also, the body's center of mass (CoM) travels as a sinusoidal path. The prosthetic foot's design (like a keel or energy-storing foot) influences how smoothly this occurs. Energy storage and return (ESAR) feet mimic the Achilles tendon and spring-like action of the foot, improving propulsion. Therefore, gait analysis in prosthetics uses biomechanical principles like kinematics (describing motion) and kinetics (forces and moments) to assess device performance and guide prosthetic fitting, ultimately improving the user's comfort, mobility, and energy efficiency.