27 Fundamental Terms: Biomechanics

Have you ever visited a foreign country and not understood the language? Entering a gym or playing a sport for the first time can be like visiting a foreign country. So here are 27 terms to help you understand how the body moves in space.

Acceleration: Change in speed or direction. Also expressed as Newton's Second Law: Force = mass x acceleration. 

    Application: In order for a basketball player to accelerate, they must experience a change in velocity from a starting position. Players who can change directions quickly through dribbling practice acceleration to move around defenders.

Agonist: Muscles acting concentrically to bring attachment sites closer to each other are agonists. Application: The biceps are agonists during a bicep curl as the bring attachment sites of the muscles closer together.

Angular Kinematics: Angular kinematics is the description of angular motion or rotation about an axis. Angles are formed by the crossing of two separate lines. Angular position can be absolute or relative. (SI Unit Radians) 

    Application: In basketball, we can measure the angles between joints to determine the optimal release points for a jump shot during different conditions using angular kinematics. The knees, hips, and wrist rotate around an axis in order to jump and produce force for a shot.

Angular Kinetics: The causes of angular motion: inertia (resistance to change), momentum, and torque. Newton’s three laws. Objects don’t change momentum without an external force acting on them. When a net force is exerted on an object, that object will move in the direction of the force applied proportional to force applied and opposite to mass. For every action, there is an equal and opposite reaction. 

    Application: During a jump shot, the triceps act to extend the ball forward while the external ball applies force in the opposite direction. 

Antagonist: Muscles that produce torque in the opposite direction during contraction. 

    Application: During a bounce pass the bicep muscles are antagonists as they resist elbow joint extension. 

Biological materials: Materials such as bone, cartilage, tendons, and ligaments. These materials carry external forces of the body, and each react differently on the stress/strain continuum. 

    Application: Harder materials experience more stress than softer materials, while softer materials experience more strain over longer periods of time. Basketball players need to train at high and low intensities to protect ligaments and tissues for the entire playing season.

Compressive forces: External forces exerting a pushing motion on the tips of internal forces. 

    Application: A chest pass received is an external pushing force that causes internal compression so that the ball can be caught.

Concentric contraction: Active muscle that draws all points of attachment closer together. A decrease in the joint angle during the upward phase of motion in most movements. 

    Application: During a jump shot a basketball player utilizes concentric contraction at the elbow joint to move the ball into position before the shot.

Contractile component: The part of the muscle that helps it to contract (bring attachment sites closer together). Actin and myosin attach and cause the muscle to contract. 

    Application: Basketball players can incorporate resistance training to help key parts of the body during a game experience growth through a contraction. The biceps and triceps can experience growth through pull-ups and dips. 

Critical features: Parts of a movement required for successful performance of the movement. Analysis of a movement is only effective if critical features are identified for a specific movement. These features include force, velocity, direction, and angular motion to name a few. 

    Application: Trainers and coaches can search for and discover the critical features relevant to a specific sport in order to increase technique and reduce injury.

Eccentric contraction: Active muscle that draws all points of attachment further apart. Normally extension or an increase of the joint angle is the visible result of an eccentric contraction. 

    Application: During a jump shot a basketball player utilizes eccentric contraction at the elbow and wrist to shoot the ball towards the hoop and make a basket.

Elastic elements: Parts of the muscular system that retain and utilize elastic energy. Tendons, connective tissue, and sarcolemma are examples. Tendons are arranged in a series and tissue are typically arranged parallel to contractile elements. 

    Application: Basketball players need to train with eccentric and concentric contractions in order to produce force at different ranges of motion (especially during a jump). Squats, cleans, and other Olympic lifts can help athletes accomplish this.

Energy: In biomechanics, energy is a person's capacity to actually do work. Two forms of mechanical energy that matter most are potential energy (PE) and kinetic energy (KE). 

    Application: A ball thrown high in the air is exerting kinetic energy, and this is transferred to potential energy as the ball begins to drop. 

External Biomechanics: The study of forces that are acting on an object. These can be broken up into contact or noncontact forces. Contact forces are important in sports because they provide friction and contact force. 

    Application: During basketball, the court is an external force that causes friction and allows the body to produce speed. Materials matter when it comes to friction, which is why basketball players use shoes with rubber soles instead of bowling shoes for example. 

Fluid Mechanics: The study of both water and air effects on movement. Fluids produce both dynamic and buoyant force. Additionally, drag and lift forces affect how objects move through space. 

    Application: When a javelin is thrown drag and lift forces affect the final distance of the javelin.

Forces: A force is defined as either a push or a pull. Forces are vectors because they have both size and direction to define them. Every force has an opposite force. Two examples in biomechanics are internal and external forces. These are forces that an object generates and forces that act on the object. (SI Unit Newton) 

    Application: Basketball players need force to act against the external environment. When a player passes a ball towards another player, they need both internal and external forces to generate movement. 

Internal Biomechanics: The study of forces that act within a system or object. 

    Application: Muscles, tendons, bones, and ligaments are internal forces that act against the environment to produce motion in a basketball game. When basketball players try to cut too hard on the court, they may experience an ankle sprain or break. This is internal or structural failure.

Isometric contraction: Active muscle that produces force without movement at either attachment site of the muscle.

    Application: Isometrics can help during rehabilitation. Practicing a wall sit is a good example of how force can be produced without movement in the rectus femoris, vastus intermedius, and hamstrings. 

Linear Kinematics: The branch of dynamics that observes and describes motion in a linear plan. Linear motion happens in the same direction at the same time (translation) and is a scalar quantity. Kinematics looks at motion without considering the forces that cause motion. 

    Application: Basketball players can increase speed (distance covered / time elapsed) through resistance training, sprint drills, and agility drills. By taking the most direct route to the ball a slower player could cover more distance quicker than a faster player in the same amount of time.

Linear Kinetics: The study of linear motion that takes into account the forces that actually cause motion. Common causes include contact and non-contact force (gravity, friction) as well as force. 

    Application: Speed is the distance traveled over time. Basketball players can increase their speed by covering greater distances in shorter times, and this can be measured through linear kinetics.

Muscular system: Comprised of smooth, cardiac, and skeletal muscles that have the ability to contract and produce tension. By acting on the levers of the skeletal system through tendons, the body can move and produce force. Muscles also help produce heat, maintain good posture, and circulate blood through the body. 

    Application: The muscular system along with the skeletal system is called the musculoskeletal system. A basketball player needs the muscles and bones to produce force against an external environment during a basketball game. 

Nervous system: Two systems combine to create the nervous system: CNS and PNS. Three basic elements of the nervous system are the motor neuron, sensory neuron, and connector neuron. The motor neuron sends signals to the muscles to produce movement. The sensory neuron relays signals from the body back to the brain after stimulation from the environment through smell, touch, or taste to name a few. Connector neurons allow different parts of the brain to communicate with each other. 

    Application: The nervous system affects how muscles activate through action potentials sent from the axon to the neuromuscular junction. Superior athletes have trained enough to increase the firing rate and the number of muscle fibers innervated per motor unit in order to outproduce other athletes.

Power: How much work a person can do in a specific amount of time. P = work done / time take to do work (SI Unit Watts). 

    Application: Power can be improved by increasing the speed of a movement or the amount of work done in a set amount of time. 

Skeletal system: Rigid levers connected to each other through joints. This system is divided between axial and appendicular parts. The skeletal system provides movement, protects organs, supports weight, and stores minerals for growth. 

    Application: During basketball, a player may run, jump, throw, and slide. This requires the muscles to pull on bones, interact with the external environment, and produce movement. 

Tensile forces: An external force pulling on the ends of an internal structure results in tensile force.     Application: When two basketball players fight for a loose ball and both pull in opposite directions, the players' muscles generate tensile force to pull the ball away from the other player. 

Torque: Rotation created when force is applied to a moment arm about an axis (fulcrum). Torque = force x radius/moment arm (SI Units newton-meters) 

    Application: Greater torque can be created by increasing either force or the moment arm during basketball. 

Work: The product of force and displacement along the line of action of a certain force. Work = force x displacement (SI Unit Joule). 

    Application: A runner who travels around a track 800m and a runner who only completes 400m could have the same amount of work as long as they start and end at the same points.

REFERENCES

1. Bussey, M & Bartlett, R. (2013). Sports Biomechanics: Reducing Injury Risk and Improving Sports Performance. Taylor and Francis. https://doi.org/10.4324/9780203867716
2. McGinnis, P. M. (2013). Biomechanics of sport and exercise. Human Kinetics.
3. Zatsiorsky, V., & Zatsiorsky, V. (Eds.). (2000). Biomechanics in sport : Performance enhancement and injury prevention. Retrieved from https://ebookcentral.proquest.com