How Bodies Move
Every step is a controlled fall. Every muscle contraction is a molecular ratchet. Biomechanics reveals the physics hidden inside living motion—the inverted pendulum of walking, the elastic spring of a tendon, the torque cascade from hip to ankle. These 10 simulations let you explore gait analysis, muscle mechanics, joint forces, spinal loading, and more. Adjust body parameters and watch the physics respond in real time.
The biomechanics of walking and running—from stance and swing phases to the inverted pendulum model that explains why we vault over our legs.
Watch a stick figure walk through all 8 phases of the gait cycle—initial contact through terminal swing—with ground reaction forces and a real-time phase bar.
Walking modeled as a series of inverted pendulum arcs. The COM vaults over the stance leg, exchanging kinetic and potential energy with each step.
Side-by-side comparison: walking uses an inverted pendulum (60% stance), running uses a spring-mass model (35% stance). See the GRF difference—1.2 vs 2.5 body weights.
The machinery of movement—from Hill’s muscle model to the elastic energy stored in every tendon spring.
Explore force-length, force-velocity, and activation curves of Hill’s three-element muscle model. Adjust parameters and see how contractile, series elastic, and parallel elastic elements combine.
The Achilles tendon as a biological spring: 93% energy return, 7% heat loss. Watch strain cycling, force-strain hysteresis, and energy storage through the gait cycle.
Free body diagrams, joint torques, inverse kinematics, and the forces that hold the skeleton together.
Drag a target and watch a multi-segment joint chain solve for position using the FABRIK algorithm. Toggle angular constraints and adjust segment count.
Free body diagram of the lower extremity showing hip, knee, and ankle moments through the gait cycle. See extension/flexion torques and ground reaction forces.
Disc compression at L4/L5 under six postures—from upright standing (1x BW) to stoop lifting (3.5x BW). See how posture and external loads affect spinal forces.
Real-world applications: prosthetic design, aquatic locomotion, and how engineering meets biology.
Compare four prosthetic types—carbon blade, passive foot, powered ankle, bionic knee—and see how stiffness and damping affect energy return and gait patterns.
Four swim strokes animated with propulsion and drag force vectors. Compare freestyle, butterfly, breaststroke, and backstroke speeds and efficiencies.