Exercise Science 2

Biomechanical Principles of Training

Objectives

• Define biomechanics

• Discuss Newton’s 3 Laws of Motion

• Review forces and vector quantities

  • Linear and angular

• Differentiate between different classes of levers

• Discuss mechanical work and power

• Discuss the length-tension relationship

Introduction

• Biomechanics:

  • A branch of science that applies principles of mechanics (study of forces) to living organisms (from Greek: bios).

  • Highlights the importance of quantifying training loads and prescribing adjustments to clients.

• Human body comparison:

  • The body is often compared to a machine that requires proper fuel to power its muscles.

  • Moveable parts include bones, joints, and muscles.

• Biomechanics view of the human body:

  • Recognizes the body as a mechanical system of movable parts, put in motion by the application of forces.

Laws of Motion

• Body movement:

  • Produced by actions of the muscular system.

  • Motion cannot occur without force.

  • Source of force in humans: Muscular system.

  • Types of motion: Linear and angular.

Linear Motion

• Linear motion (translation): Motion along a line.

  • Rectilinear motion: Motion along a straight line.

  • Curvilinear motion: Motion along a curved path.

• Linear displacement: Distance that a system moves in a straight line.

Angular Motion

• Angular motion (rotation): Rotation around an axis provided by various joints.

• Relation between Linear and Angular motion:

  • Angular motion of the joints produces the linear motion of actions such as walking.

Newton's Laws of Motion

• 1st Law - Law of Inertia:

  • A body in motion tends to remain in motion at the same speed in a straight line unless acted upon by an external force; a body at rest tends to remain at rest unless acted upon by a force.

  • Muscles generate force to start, stop, accelerate, decelerate, and change the direction of motion.

  • Inertia: The greater an object's mass, the greater its inertia. More force is required to significantly change an object’s inertia if it is larger.

• 2nd Law - Law of Acceleration:

  • Mathematical expression: $F = m imes a$ where:

  • F = Force

  • m = Mass

  • a = Acceleration.

  • Force is measured in Newtons (1 kg × 1 m/s²).

  • Acceleration: The rate of change in velocity; a strong muscular force is essential for speed.

  • Mass: The amount of matter in the body affecting speed and acceleration.

  • Example: Greater force is needed to accelerate a 230-pound man than a 130-pound man to the same speed; a baseball may be accelerated faster than a shot due to weight differences.

• 3rd Law - Law of Reaction:

  • A force does not act alone on an object.

  • For every action force exerted, there is an equal and opposite reaction force.

  • Example of Linear Movement: Ground Reaction Force (GRF) - the action force is provided by the body, and the surface responds with an equal reaction force.

  • Running on Different Surfaces: Running on a hard track is easier than on sand due to different ground reaction forces; the track resists propulsion while aiding the runner's forward motion.

Force and Vector Quantities

• A force is defined as a push or pull.

  • Requires an agent (something exerting power).

  • Acts upon an object.

  • Mathematical formula: $F = m imes a$

  • Forces are vector quantities, meaning they have both magnitude (size) and direction, denoted as F.

Resolving Vector Quantities into Components

• Identify the angle of the vector in relation to a reference direction (horizontal, vertical, or X-Y axes).

• Identify the magnitude of the vector, expressible in newtons, meters per second, etc.

• Components Calculation:

  • Use the formulas:

  • $component1 = magnitude imes ext{sin(angle)}$

  • $component2 = magnitude imes ext{cos(angle)}$

  • The first formula gives the component opposite the angle; the second gives the adjacent component.

Example of Vector Quantities

• Barbell Curl:

  • Muscle contraction forces are directed both perpendicularly and parallel to the forearm during the movement.

  • This action is illustrated in Figure 4.3.

Rotation

• Rotational Movements:

  • Measured using moment of force/torque.

  • Torque: Defined as the tendency of a force to cause rotation, mathematically expressed as:

  • $Torque = Force imes d_{ ext{perpendicular}}$

  • Or M = F imes d_{ot} where

  • M = Moment of force

  • F = Force

  • d = Perpendicular distance from the axis of rotation.

• Example Comparison of Deadlifts:

  • A standard deadlift versus a hex deadlift demonstrates differences in lever arms, resulting in different torque moments explained further.

Levers

• Humans as lever systems:

  • A lever is defined as a rigid bar that rotates around an axis (fulcrum) used to increase the amount of resistance that can be overcome by applying force.

• Operation of Levers:

  • Rotate about a pivot point (the axis) because force is applied to move against resistance or weights.

  • In human anatomy terms:

  • Bones act as bars,

  • Joints function as axes of rotation,

  • Muscles provide the force through contraction.

Classification of Levers

• Classified by the arrangement of forces (fulcrum, load/resistance, and applied force):

  • Class 1: Fulcrum in the middle (example: seesaw).

  • Class 2: Load/resistance in the middle (example: wheelbarrow).

  • Class 3: Force in the middle (example: shoveling).

• Illustrations of Classifications:

  • Reference Figure 4.5 for visual representation of each lever class.

Quantifying Training Effects

• Client interest in knowing which strength training routine provides the greatest training volume:

  • Strength Training Routine: 3 sets of 10 repetitions at 200 lb.

  • Endurance Training Routine: 3 sets of 15 repetitions at 150 lb.

Mechanical Work

• Mechanical Work Definition:

  • The product of the magnitude of a force that creates a change in position multiplied by linear displacement.

  • Formula: $W = F imes D$ (where $W$ = work, $F$ = force, $D$ = distance).

  • Example: A squat bar moving vertically 2 ft with 200 lb of force:

  • $W = 200 ext{ lb} imes 2 ext{ ft} = 400 ext{ ft} ext{ lb}$.

Total Work Calculation for Resistance Training Routines

• Strength Routine:

  • Sets: 3

  • Repetitions: 10

  • Force-Load: 200 lb

  • Displacement: 3 ft

  • Total Work: $(F imes D) imes (R imes S)$

• Endurance Routine:

  • Sets: 3

  • Repetitions: 15

  • Force-Load: 150 lb

  • Displacement: 3 ft

Mechanical Work for Rotational Movements

• Angular Work:

  • Defined as the product of angular momentum and angular displacement.

  • Formula: $ext{Angular Work} = M imes ext{Δθ}$

  • This works with positive and negative work considerations.

Power

• Power Definition:

  • Refers to the rate at which work is performed.

  • Mathematical expression: $P = rac{W}{t}$ (linear)

    • Or can also be expressed as: $P = F imes rac{d}{t}$ or $P = F imes V$ where $V$ is velocity.

• Example Comparison:

  • Strength Power: 18,000 lb/ft over 20 minutes.

  • Endurance Power: 20,250 lb/ft over 30 minutes.

  • This illustrates which routine demands more power.

Power for Rotational Movements

• Angular Power:

  • Defined as: $ext{Angular Power} = M imes ω$ where:

  • M = Angular moment

  • ω = Angular velocity.

  • Example: Wheelchair propulsion demonstrates how tangent force contributes to rotational power calculations.

Muscular Anatomy and Force

• Active Muscle Force (Tension):

  • Force generated during muscular contraction that is under individual control.

• Passive Muscle Force:

  • Generated through an external force applied to pre-stretch a muscle,

  • Where placing the muscle in a stretched position can create beneficial passive forces that become beneficial when the muscle is subsequently shortened (similar to a rubber band).

Length-Tension Relationship

• Maximal Force Generation:

  • Occurs at normal resting muscle lengths.

• Increased Capacity:

  • Force generation capacity enhances when the muscle is slightly pre-stretched, interacting with both active and passive components.

• Depicted in the combined force curve showing the active, passive, and total muscle forces.

Application of Length-Tension Relationship

• Jump-Reach Test:

  • Illustrates the practical application of the length-tension relationship, especially when jump muscles are pre-stretched (e.g., partial squat prior to the jump).

Force-Velocity Relationship

• Demonstrated by the relationship showing that during shortening or concentric actions, maximal force declines as shortening velocity increases;

  • A notable peak in force occurs during eccentric (lengthening) contractions around 12.5% of the maximal lengthening velocity achieved.