Biomechanics Cheat Sheet
The core ideas of Biomechanics distilled into a single, scannable reference — perfect for review or quick lookup.
Quick Reference
Newton's Laws Applied to Human Movement
Newton's three laws of motion form the foundation of biomechanical analysis. The first law (inertia) explains why a body at rest stays at rest unless acted upon by an external force. The second law (F = ma) relates the net force on a body to its mass and acceleration. The third law (action-reaction) explains ground reaction forces during walking and running.
Kinematics
The branch of mechanics that describes the geometry of motion without reference to the forces causing it. In biomechanics, kinematics involves measuring joint angles, linear and angular velocities, and accelerations of body segments during movement using motion capture systems.
Kinetics
The study of forces and torques that cause or result from motion. In biomechanics, kinetics examines ground reaction forces, joint reaction forces, muscle forces, and joint moments. It answers why movement occurs, complementing the descriptive nature of kinematics.
Stress and Strain in Biological Tissues
Stress is the internal force per unit area within a material, while strain is the deformation (change in length relative to original length) that results. Biological tissues such as bone, cartilage, tendon, and ligament exhibit complex stress-strain behaviors including viscoelasticity, anisotropy, and nonlinearity.
Muscle Mechanics and the Hill Model
The Hill muscle model represents skeletal muscle as a three-component system: a contractile element (active force generation), a series elastic element (tendon), and a parallel elastic element (passive tissue). The force-velocity and force-length relationships of the contractile element govern how much force a muscle can produce under different conditions.
Center of Mass and Balance
The center of mass (COM) is the point where the total mass of a body can be considered concentrated. For stable standing, the vertical projection of the COM must fall within the base of support. Biomechanists analyze COM trajectories to assess balance, stability, and energy expenditure during locomotion.
Inverse Dynamics
A computational method that combines kinematic data (motion capture), kinetic data (force plates), and body segment parameters (mass, moment of inertia) to calculate the net forces and moments acting at each joint. This is the primary method for estimating internal joint loading during movement.
Viscoelasticity
The property of biological materials that exhibit both viscous (time-dependent, energy-dissipating) and elastic (energy-storing) behavior when deformed. Viscoelastic tissues display creep (continued deformation under constant load), stress relaxation (decreasing stress under constant deformation), and hysteresis (energy loss during loading-unloading cycles).
Wolff's Law and Mechanotransduction
Wolff's Law states that bone remodels in response to the mechanical loads placed upon it, becoming stronger where loads are high and weaker where loads are low. The underlying cellular process, mechanotransduction, converts mechanical stimuli into biochemical signals that regulate tissue growth, maintenance, and repair.
Fluid Mechanics in Biological Systems
Biofluid mechanics applies principles of fluid dynamics to biological flows, including blood flow through the cardiovascular system, air flow in the respiratory system, and synovial fluid lubrication in joints. Key concepts include viscosity, laminar versus turbulent flow, and the Navier-Stokes equations.
Key Terms at a Glance
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