​

A

• Abduction: Movement of a limb or body part away from the midline of the body. Think of lifting your arm out to the side.
• Acceleration: The time derivative (rate of change) of velocity, m/s^2.
• Adduction: Movement of a limb or body part toward the midline of the body. Bringing your arm back down to your side.
• Angular Velocity: The rate of change of angular position of a rotating body, usually expressed in degrees per second (°/s) or radians per second (rad/s). This is a key metric for understanding the speed of rotation during a pitch or swing.
• Anterior: Situated at or directed toward the front of the body.
• Axis of Rotation: an imaginary line about which an object rotates. It’s a fixed point or line that remains stationary while the rest of the object moves in a circular path around it. The center line of the knee joint generally acts as the axis of rotation for knee flexion and extension.

​

B

• Base of Support: The area or distance covered on the ground enclosed by points of contact with the body (such as feet). A wider base generally provides more stability.
• Biomechanics: The study of how biological systems respond to mechanical forces, applying principles of physics to understand how organisms move and interact with their environment.
• Biomechanical Efficiency: The ability to produce a desired movement outcome with minimal energy expenditure and/or stress on the body. This is a key goal for maximizing performance and preventing injury.

​

C

• Center of Mass (CoM): The point in an object or system that responds to external forces as if the total mass of the system were concentrated at this point. Understanding how the CoM shifts based on body segment positioning is vital for balance and force generation. Also known as the center of gravity.
• Circumduction: A conical or circular movement of a limb, combining flexion, extension, abduction, and adduction. Think of drawing a circle with your arm.
• Co-contraction: The simultaneous activation of opposing muscles around a joint. While some co-contraction is necessary for stability, excessive co-contraction can reduce efficiency. For example, co-contracting the biceps and triceps stabilizes the elbow joint. Also known as co-activation.
• Concentric: When a muscle generates force and shortens, opposite of eccentric. For example, during the upward phase of a bicep curl, the biceps muscle is acting concentrically.

​

D

• Distal: Situated away from the center of the body or the point of attachment. Your hand is distal to your elbow.

​

E

• Eccentric: General term for the phase when a muscle is lengthening under tension. This is crucial for deceleration and controlling movements. For example, walking down stairs and lowering a dumbbell from a bicep curl are eccentric motions.
• Extension: Straightening a joint, increasing the angle between the bones.
• External Rotation: Rotation away from the midline of the body. For the throwing shoulder, this is a critical phase for building potential energy.

​

F

• Flexion: Bending a joint, decreasing the angle between the bones.
• Frames per second (fps): How many frames a camera records per second, also known as hertz (Hz). Uplift can record movements at 30, 60, 120, and 240 frames per second. Uplift records faster motions at higher fps in order to measure the motion more accurately.
• Force: An interaction that, when unopposed, will change the motion of an object. Measured in Newtons (N). Understanding the forces generated during a swing or pitch is essential.
• Force Plate (or Platform): A device that measures the ground reaction forces exerted by an individual during movement.
• Frontal Plane: Movement in the frontal plane is side to side and up and down. This plane splits the front and back portions of the body. Also known as the cartwheel plane. Jumping jacks and the “YMCA” dance primarily occur in this plane.

​

G

• Global Coordinate System (GCS): This provides an absolute reference frame in space for defining the position and orientation of body segments or instruments. It’s typically a fixed, 3D cartesian coordinate system (x, y, z) with a defined origin (0,0,0). The GCS is used to describe the overall movement of a body or system, while local coordinate systems define the movement of individual segments relative to each other.
• Gravity: a fundamental force of attraction between any two objects with mass or energy. In biomechanics, this is simplified as a constant acceleration value of g = 9.81 m/s acting straight down through the global coordinate system. Gravitational force is calculated by multiplying g by an object’s mass in kg.
• Ground Reaction Force (GRF): The force exerted by the ground on a body in contact with it. Newton’s Third Law states that for every action, there is an equal and opposite reaction. Analyzing GRF helps understand how an athlete interacts with the ground to generate power.
• Goniometer: A hand-held device used to measure a joint angle, it looks like a protractor with a long arm to help with aligning along a body segment.

​

I

• Inertia: The tendency of an object to resist changes in its state of motion. A heavier object has more inertia than a light object if both objects have the same motion state.
• Internal Rotation: Rotation toward the midline of the body. In throwing, this is a powerful movement that accelerates the arm.

​

J

• Jerk: the time derivative (rate of change) of acceleration (m/s^3). This is not commonly used outside of signal processing of acceleration data.

​

K

• Kinematics: The study of motion without considering the forces causing the motion. This includes displacement, velocity, acceleration, and angles. Uplift focuses on kinematic analysis because it does not measure forces.
• Kinetics: The study of motion with consideration of the forces causing the motion. This involves analyzing forces, torques, and momentum.

​

L

• Lag: A delay or offset in the timing of different body segments during a movement. Optimal lag in movements like throwing can contribute to increased velocity.
• Lateral: Situated away from the midline of the body.
• Linear Velocity: The rate of change of linear position, usually expressed in meters per second (m/s). Important for understanding the speed of the ball or the athlete’s movement.
• Local Coordinate System (LCS): a coordinate system defined entirely within an object, with its own origin, axes, and scale. Uplift uses LCSs to calculate joint angles, for example, we create a torso LCS and an upper arm LCS to calculate the shoulder joint angles.

​

M

• Medial: Situated toward the midline of the body.
• Momentum: The product of an object’s mass and its velocity (p=mv). Conservation of momentum plays a role in multi-segment movements.
• Motion Capture: The process of recording the movement of objects or people, often using specialized cameras and markers.

​

N

• Newtons: SI unit of measurement for force. 1 Newton = 0.225 pounds.

​

P

• Posterior: Situated at or directed toward the back.
• Pronation: Rotation of the forearm so that the palm faces posteriorly (thumb facing downward or backward). Also refers to the inward rolling motion of the foot during gait.
• Proximal: Situated close to the center of the body or the point of attachment. Your shoulder is proximal to your elbow.

​

R

• Range of Motion (ROM): The full movement potential of a joint, typically measured in degrees. Maintaining adequate ROM is crucial for performance and injury prevention.
• Rotation: Movement around an axis. Essential for generating power in throwing and hitting.

​

S

• Sagittal Plane: The sagittal plane is a vertical plane which passes through the body from front to back. It divides the body into a left section and a right section. Also known as the somersault plane. Walking, running, and somersaulting primarily occur in this plane.
• Scapular Loading: The process of retracting and protracting the scapula (shoulder blade) to store elastic energy during the wind-up phase of throwing. Efficient scapular loading is linked to higher throwing velocities.
• Segmental Coordination: The timing and sequencing of movements of different body segments. Optimal coordination allows for efficient transfer of energy throughout the kinetic chain.
• Stability: The ability to resist disturbance to one’s equilibrium. Important for maintaining balance during dynamic movements.
• Supination: Rotation of the forearm so that the palm faces anteriorly (thumb pointing upward or forward). Also refers to the outward rolling motion of the foot during gait.

​

T

• Torque: A rotational force, calculated as the product of force and the perpendicular distance from the axis of rotation (moment arm) (τ = r × F). Torque is what causes rotation at the joints.
• Transverse Plane: The transverse plane, also known as the axial plane or horizontal plane, divides the body into superior (top) and inferior (bottom) halves. Twisting and turning motion occurs in this plane.
• Trunk Rotation: The twisting movement of the torso around the spine. A critical component for generating power in baseball movements.

​

V

• Valgus: Angulation of a joint such that the distal segment is deviated laterally (away from the midline). Often discussed in the context of elbow stress during a throw or knee motion under high force. Can also be thought of as knock-kneed.
• Varus: Angulation of a joint such that the distal segment is deviated medially (toward the midline). Can also be thought of as bow-legged.
• Velocity (linear): The rate of change of position with respect to time, including both speed and direction. Crucial for analyzing the speed of body segments and the ball.

​

X

• X Factor: Typically for baseball or movements that require a large amount of body twisting motion. X Factor refers to the transverse plane difference between the pelvis (hip to hip) and torso (shoulder to shoulder) angles because it creates an “X” when nonzero as viewed from above. Also known as hip-shoulder separation.