In biomechanics, understanding movement and stability requires knowledge of key fundamental concepts like axes and planes, center of gravity, equilibrium, and line of gravity. These concepts help in analyzing human motion, improving athletic performance, and preventing injuries.
1. Axes and Planes
A. Axes of Motion
An axis is an imaginary line around which the body or a body part rotates. There are three primary axes of motion:
- Frontal Axis (Coronal Axis)
- Runs side to side (left to right).
- Movements around this axis include flexion and extension (e.g., forward bending in a sit-up).
- Sagittal Axis (Anteroposterior Axis)
- Runs front to back (anterior to posterior).
- Movements around this axis include abduction and adduction (e.g., side leg raises).
- Vertical Axis (Longitudinal Axis)
- Runs top to bottom (head to toe).
- Movements around this axis include rotational movements (e.g., spinning in a ballet turn).
B. Planes of Motion
A plane is an imaginary flat surface that divides the body and along which movements occur.
- Sagittal Plane
- Divides the body into left and right halves.
- Movements: Flexion and extension (e.g., forward lunges, bicep curls).
- Frontal Plane
- Divides the body into front and back halves.
- Movements: Abduction and adduction (e.g., jumping jacks, lateral raises).
- Transverse Plane
- Divides the body into upper and lower halves.
- Movements: Rotation, twisting (e.g., turning the head, twisting at the waist).
2. Centre of Gravity (COG)
Definition
The center of gravity (COG) is the point where the entire weight of a body or object is evenly distributed and balanced in all directions.
Key Points
- It is the imaginary point where the body’s mass is concentrated.
- In a standing human, the COG is near the navel (just in front of the second sacral vertebra).
- The COG shifts when a person moves, bends, or carries a load.
- A lower COG increases stability, while a higher COG decreases it (e.g., a wrestler lowers their stance to improve balance).
3. Equilibrium
Definition
Equilibrium is the state of balance where all external forces acting on a body are equal, preventing movement or maintaining controlled motion.
Types of Equilibrium
- Static Equilibrium – When the body is at rest and not moving (e.g., a gymnast holding a handstand).
- Dynamic Equilibrium – When the body is in motion but remains balanced (e.g., a cyclist maintaining balance while riding).
Factors Affecting Equilibrium
- Base of Support (BOS): A wider stance provides better stability.
- Height of Centre of Gravity: A lower COG improves balance.
- Mass of the Body: More mass increases stability.
- Position of Line of Gravity: If the line of gravity falls within the base of support, stability is maintained.
4. Line of Gravity (LOG)
Definition
The Line of Gravity (LOG) is an imaginary vertical line that passes through the centre of gravity and extends toward the ground.
Key Points
- It determines stability – when LOG is within the Base of Support (BOS), balance is maintained.
- If the LOG moves outside the BOS, the body loses balance and may fall.
- Athletes use their LOG strategically, such as leaning forward in a sprint start to create forward momentum.
Conclusion
These fundamental concepts of biomechanics are essential for understanding human movement, improving performance, and preventing injuries in sports and physical activities. By applying principles of axes and planes, centre of gravity, equilibrium, and line of gravity, athletes and trainers can enhance stability, efficiency, and control in motion.