Chapter 8: Fundamentals of Kinesiology & Biomechanics in Sports

8.1 Meaning and Importance

Kinesiology

Kinesiology (from Greek kinesis meaning movement, and logia meaning study) is the scientific study of human or non-human body movement. Applications include biomechanics, orthopedics, physical therapy, and sport psychology.

Biomechanics

Biomechanics is the study of the structure and function of biological systems by means of the methods of mechanics. It applies the laws of physics and mechanics to living organisms, particularly comparing the human body to a machine.

Importance in Sports

1. Improves Technique: Helps athletes optimize movement to achieve peak performance (e.g., finding the perfect release angle for a javelin).
2. Equipment Design: Aids in developing aerodynamic gear, shock-absorbing shoes, and lighter rackets.
3. Injury Prevention: Highlights forces (like sheer stress) acting on joints to avoid hazardous techniques.

8.2 Newton’s Laws of Motion & Their Application in Sports

Sir Isaac Newton formulated three fundamental laws of classical mechanics describing the relationship between a body and the forces acting upon it.

1. Law of Inertia (Newton’s First Law)

“An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an external net force.”

• Formula: \[ \Sigma F = 0 \implies \frac{dv}{dt} = 0 \]
• Application: A football placed on the ground will not move until a player kicks it (applying external force). A sprinter sprinting down the track will continue moving forward after the finish line until they apply braking forces using muscle friction and gravity.

2. Law of Acceleration (Newton’s Second Law)

“The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.”

• Formula: \[ F = m \times a \implies a = \frac{F}{m} \]
• Application: In shot put, the heavier the shot (mass), the more force is required to accelerate it. A larger, stronger athlete can apply more force, accelerating the shot faster, making it travel further.

3. Law of Action and Reaction (Newton’s Third Law)

“For every action, there is an equal and opposite reaction.”

• Formula: \[ F_{AB} = -F_{BA} \]
• Application: When a swimmer pushes the water backward with their hands (action), the water pushes the swimmer forward with an equal force (reaction). When a high jumper pushes down hard onto the ground (action), the ground exerts an enormous upward force (reaction) launching them into the air.

8.3 Types of Levers and Their Application in Sports

A lever is a rigid rod that turns around a fixed point called a Fulcrum (F). The force applied is the Effort (E), and the weight moved is the Load/Resistance (R).

• Class I Lever (( F ) in the middle): Load - Fulcrum - Effort.

  • Example in Body: Nodding the head. The fulcrum is the top vertebra, load is the front of the skull, effort is the neck muscles pulling down the back of the skull.
  • Sports Example: Rowing an oar.

• Class II Lever (( R ) in the middle): Fulcrum - Load - Effort.

  • Example in Body: Standing on tiptoes. The fulcrum is the toes, load is body weight on the ball of the foot, effort is the calf muscle pulling the heel up.
  • Sports Example: Doing a push-up.

• Class III Lever (( E ) in the middle): Fulcrum - Effort - Load.

  • Example in Body: Bicep curl. The fulcrum is the elbow joint, effort is the bicep muscle attached just below the elbow, load is the dumbbell in the hand.
  • Note: Class III levers are the most common in the human body. They favor a wide range of motion and speed over heavy force.

Mechanical Advantage Formula:

\[ MA = \frac{\text{Effort Arm length}}{\text{Resistance Arm length}} \] If ( MA > 1 ), it requires less effort to move a large load (Class II). If ( MA < 1 ), it requires greater effort but moves the load faster and further (Class III).

8.4 Axis and Planes

All human movement takes place in specific geometric planes and around specific geometric axes.

Planes of the Body

1. Sagittal Plane: Divides the body vertically into left and right halves.
   • Example Movements: Flexion and extension (e.g., running, bicep curls, nodding yes).
2. Frontal (Coronal) Plane: Divides the body vertically into front and back halves.
   • Example Movements: Abduction and adduction (e.g., jumping jacks, cartwheels).
3. Transverse (Horizontal) Plane: Divides the body horizontally into top and bottom halves.
   • Example Movements: Rotation (e.g., spinning in ice skating, twisting the torso).

Axes of the Body

1. Frontal-Horizontal Axis: Passes horizontally from side to side. (Perpendicular to Sagittal plane).
2. Sagittal-Horizontal Axis: Passes horizontally from front to back. (Perpendicular to Frontal plane).
3. Vertical (Longitudinal) Axis: Passes straight down from the top of the head. (Perpendicular to Transverse plane).

8.5 Friction and Projectile in Sports

Friction in Sports

Friction is the resistance that one surface or object encounters when moving over another.

• Static Friction: The force keeping an object stationary (e.g., spikes of track shoes gripping the starting blocks).
• Dynamic/Kinetic Friction: The opposing force between moving surfaces (e.g., ski blades gliding on snow).
• Role in Sports: Friction can be advantageous (like basketball shoes squeaking to stop quickly) or disadvantageous (air friction slowing down a cyclist, hence the need for aerodynamic helmets).

Projectile Motion in Sports

An object thrown into space is a projectile. Its path is called its trajectory.

• Goal in Sports: To achieve maximum horizontal range (e.g., javelin throw, long jump) or vertical height (e.g., high jump).
• Factors affecting trajectory:
  1. Angle of Release: Theoretically, an angle of 45 degrees achieves the maximum horizontal distance.
  2. Speed/Velocity of Release: Higher speed leads to geater distance.
  3. Height of Release: Launching from a higher point extends the horizontal range.
  4. Air Resistance: Slows down the projectile.

Equation of Trajectory (Range): \[ R = \frac{v^2 \sin(2\theta)}{g} \] (Where R is Range, v is initial velocity, (\theta) is the angle of release, and g is gravity).