Introduction to Biomechanics

What is Biomechanics?

• The application of mechanical laws to living structures.
• The study of forces acting on or produced by the human body (external or internal forces).
• Biomechanics is applicable to the technique realm.

Kinetics

• The study of the relationship between the force system acting on a body and the changes it produces in a body motion.

Kinematics

• A branch of mechanics which deals with the geometry of the motion of objects, including displacement, velocity and acceleration without taking into account the forces that produce the motion.

Biomechanics Applications

• Understanding gymnastics skills.
• Analyzing and teaching skills.
• Identifying causes of errors.
• Correcting errors.
• Applying knowledge to changes in apparatus and rules.
• Evaluating new innovations.

New Vault Table

• Increased approach velocity.
• Shorter pre-flight times.
• Safer and more comfortable wrist position.
• Advantage for applying vertical forces.
• Increased friction (safety and force application).

Types of Biomechanical Analysis

• Quantitative biomechanical analysis - used in scientific studies, requires more preparation time, technological resources for data collection, laborious statistical analysis.
• Qualitative biomechanical analysis - useful for identifying movement parameters and deviations, describing positions and phases, actions, explaining causes, mechanisms, principles, predicting effects, techniques, methodologies, recommending physical or technical corrections,.

Forces

• Force - considered as the pushing or pulling action that one object exerts on another.
• Force - any cause that changes or tends to change the velocity or shape of an object.
• Newton (N) - the international system of units (SI) unit of force.
• F - symbol for force vector.
• Internal forces - generated by muscles and transmitted by tendons, bones, ligaments, and cartilage.
• External forces - weight, reaction forces, friction.
• Resultant Force - if several forces act simultaneously, their combined effect can be represented by this single force.

External Forces

• Force of gravity (weight) - the force of attraction between any two masses.
• Centripetal force - a force that makes a body follow a curved path.
• Ground reaction force - a force exerted by a surface on an object in contact with it.
• Frictional force - a force that opposes motion between two surfaces in contact.
• Impulse force - a force that acts over a short period of time.
• Torque - a force that causes rotation.

Newton's Laws of Motion

• First Law of Motion (Law of Inertia) - a body at rest will remain at rest, and a body in motion will remain in motion unless acted upon by an external force.
• Second Law of Motion (Law of Acceleration) - the force action on an object is equal to the mass of the object times its acceleration (F=m.a).
• Third Law of Motion (Law of Action) - for every action force there is a reaction force equal in magnitude, opposite in direction, and simultaneous.

The Principle of Action-Reaction in the Air

• It's not possible to move body part A towards body part B without simultaneously moving body part B towards body part A.
• This is the basis for generating 'indirect' ground reaction forces when in contact with the floor or apparatus.
• When a body part is extended upward, the body must move downward and vice versa.
• When a body part is extended sideways, the body must tilt in the opposite direction.
• When the legs are extended forwards, the trunk must come forwards, and vice versa.
• When the upper body is twisted to the right, the lower body must twist to the left, and vice versa.

Kinematics

• Velocity - measure of how far the body has moved in a specific period of time (average velocity) or of how fast it is moving (instantaneous velocity).
• Acceleration - a measure of how much a body's velocity changes overtime.
• Deceleration - negative acceleration (decrease in velocity).

Static Positions

• Mass - quantity of matter that an object contains.
• Weight - the gravitational attraction between 2 objects.
• Force of Gravity - the force of attraction between any two masses.
• Center of Mass / Center of Gravity (COM) - the point about which a body is equally balanced in all directions.
• Center of Mass (COM) - the point at which the body's total mass is considered to be concentrated.

Principles of Stability

• Stability - resistance to linear and angular motion.
• Balance - the ability to maintain a stable position.
• The Lower the COM to the base of support, the greater the stability.
• The larger the base of support, the greater the stability.
• The nearer the COM is over the center of the base of support, the greater the stability.
• In a segmented body, the better the vertical alignment of the COM’s of the individual segments, the greater the stability.

Applied Biomechanics

• Direct Ground Reaction Force - the reaction to a 'direct action' force applied by the gymnast.
• Indirect Ground Reaction Force - the reaction to a 'reaction action' applied by the gymnast.
• Jumping - downwards pushing the legs results (F ACTION) in an upwards direct (GROUND) reaction force (F REACTION).
• Swinging arms up (DIRECT ACTION) - body wants to go down (DIRECT REACTION) and increases reaction force upward (INDIRECT REACTION FORCE).

Mechanics of Spring

• An action force must be applied that generates a reaction force large enough to overcome the force of gravity.
• Can be from internal forces (muscular contractions).
• Can be from external forces (mini tramp, bar, springboard, etc.).

Effective Force Application is Related to

• Magnitude - strength in all active muscles.
• Point of Application - (off center = rotation).
• Direction - always opposite to application.
• Duration - range of motion/flexibility.
• Timing - coordination.
• Rigidity of the body - body tension and shape.

Magnitude of Force

• Must be sufficient for the desired outcome (optimal vs maximal).
• Strength and power in all active muscles.

Direction of Force

• Must be in the desired direction.
• Remember "action force > reaction force".

Duration of Force

• Must be over the longest time and distance possible.
• Range of motion/flexibility in all active joints.

Time of Force

• Sequential summation of forces.
• Largest to smallest.
• Proximal to distal.
• Coordination.

Force Applied to Rigid Body

• Otherwise forces will be used or "wasted" to change the shape of the body.
• Body tension and shape.

Take-Off Force

• At the instant of take-off, these are determined:
• Angle (º) of take-off and landing (COM).
• Vertical velocity up (Vz) (reduced to zero by gravity).
• Vertical velocity (Vz) on landing = Initial vertical velocity (V0z).
• Horizontal velocity (Vx).
• Height (= Time).
• Distance.
• Direction.

Time in the Air (= Height)

Rotational Momentum

• Body shape (= potential to change speed of rotation).

Total Mechanical Energy

• Total Mechanical Energy (= Potential Energy + Kinetic Energy).

Biomechanics in Gymnastics

• Biomechanics applies mechanical principles to understand the forces acting on the human body, particularly during gymnastics.
• Kinetic study focuses on force and its effect on motion.
• Kinematics focuses on the geometry of motion without considering the forces involved.

Applications of Biomechanics in Gymnastics

• Applying biomechanics helps understand, analyze, and teach gymnastics skills.
• It helps identify causes of errors, suggest corrective actions, and evaluate new innovations.
• The new vaulting table is an example of biomechanical innovation aimed at improving safety and enhancing performance.

Types of Biomechanical Analysis

• Qualitative analysis involves observing and describing movement characteristics.
• Quantitative analysis uses measurements and data to quantify and analyze movement.

Forces in Gymnastics

• Gymnasts experience both internal and external forces.
• External forces include gravity, reaction forces, and friction.
• Resultant force represents the combined effect of multiple forces acting on the body.

Newton's Laws of Motion

• The first law describes inertia - a body's tendency to resist changes in its state of motion (rest or uniform motion).
• The second law states that force is directly proportional to mass and acceleration (F=ma).
• The third law states for every action force, there is an equal and opposite reaction force.

Principle of Action-Reaction

• Explains how forces are generated in the air using body parts.
• Moving a body part in one direction automatically causes an opposite movement in another part.

Kinematics Concepts

• Velocity measures how fast an object moves (m/s).
• Acceleration measures how much velocity changes over time (m/s2).
• Gravity (9.81 m/s2) causes downward acceleration.

Static Positions in Gymnastics

• Mass is the quantity of matter in an object and remains constant.
• Weight is the gravitational force on an object and varies depending on location.
• Center of Mass (COM) is the point where the body's total mass is concentrated.
• It's crucial to understand COM for stable positions and movements.

Principles of Stability and Balance

• Stability is the resistance to linear and angular motion.
• Balance is the ability to maintain a stable position.
• Stability is influenced by COM position, base of support size, and vertical alignment of body segments.

Applied Biomechanics: Indirect Ground Reaction Forces

• Indirect ground reaction forces are generated in response to a reaction force that's initiated by the gymnast.
• Examples include jumping, swinging arms up, and extending legs forward.

Biomechanics of Springing and Force Application

• Effective force application is critical for achieving desired movements.
• Key factors include magnitude, point of application, direction, duration, timing, and rigidity of the body.

Factors in Force Application

• Magnitude: Sufficient force based on strength and power of muscles.
• Direction: Must be consistent with the desired movement.
• Duration: Applying force over the longest time and distance possible.
• Timing: Coordination and sequential summation of forces.
• Rigidity: Body tension and maintaining a rigid structure.

Biomechanical Analysis of Take-Off

• Analyzing take-off involves measuring factors like take-off angle, vertical velocity, horizontal velocity, height, distance, and direction.

Rotational Momentum and Total Mechanical Energy

• Body shape influences rotational momentum.
• Total mechanical energy is the sum of potential and kinetic energy.