7.9 Chapter Summary
Key Takeaways
- Biomechanics bridges biology and mechanics: Biomechanics is the scientific study of how forces interact with living bodies, especially human movement. It combines knowledge of living systems (“bio”) and physical forces (“mechanics”) to explain how motion occurs and how it can be optimized.
- Forces influence movement and come from inside and outside the body: Internal forces, such as muscle contractions (concentric, eccentric, isometric), originate within the body, while external forces like gravity, wind, and friction come from the environment and impact our movement capabilities and stability.
- Newton’s Laws of Motion:
- The First Law (Inertia) explains that an object at rest remains at rest, or if in motion, remains in motion at a constant velocity unless acted on by a net external force.
- The Second law ([latex]F = ma[/latex]) explains that a force applied to an object is directly proportional to the magnitude and direction of the resultant acceleration of that object, but inversely proportional to the object’s mass.
- The Third law explains that for every action, there is an equal and opposite reaction that exists both in magnitude and direction against the object from which the force originated.
- Three classes of Levers in the body to aid movement: The body uses three types of levers involving bones, joints (fulcrums), and muscles.
- First-class: balanced motion (e.g., head nodding).
- Second-class: strength advantage (e.g., calf raise).
- Third-class: speed and range advantage (e.g., biceps curl).
- Stability depends on mass, COM, and BOS: Stability is greatest when the center of mass (COM) is low and falls within a wide base of support (BOS). Adjusting body posture and contact points helps maintain or regain equilibrium, especially during movement or impact.
- Maximum force requires full joint movement and proper sequencing: To generate maximum force in movement (e.g., throwing or serving), the body must utilize its full range of motion (ROM) and coordinate joint activation from large to small muscle groups in the correct order.
OpenAI. (2025). ChatGPT. [Large language model]. https://chat.openai.com/chat
Prompt: Summarize the following content into six key takeaways.
Key Terms
- Acceleration: The rate at which an object changes velocity or how fast or slow an object speeds up or slows down.
- Applied Force (Effort): Typically causes the motion and is often triggered via muscle contraction.
- Base of support (BOS): The area beneath a person or object that includes every point of contact that supports it against gravity (feet, hands or any other body part touching the ground or another surface. A larger and wider BOS increases stability.
- Biomechanics: A broad class of science which involves the study of movement in living things.
- Centre of mass (COM): The imaginary center point at which the mass of an object is equally distributed.
- External forces: All forces that originate outside the body, such as gravity ([latex]9.81 \, \text{m/s}^2[/latex])., wind, and friction.
- Force: A force, which is measured in Newtons (N), is something that acts on or from within the body to either help or hinder movement, and it can come from a variety of sources, either in isolation or simultaneously.
- Fulcrum: Where the lever arm (or joint) pivots. Also known as “axis of rotation”.
- Gravity: This is the force that pulls us toward the ground and on Earth. It is assumed to be constant at 9.81 m/s2.
- Inertia: The ability of an object to resist changes in its motion (resist acceleration)
- Internal forces: All forces that originate within the body. These forces are typically generated through skeletal muscle contraction (concentric, isometric, eccentric).
- Lever Arm: A “bar-like” structure which is used to transmit force.
- Lever system: A lever system contains a lever arm, a fulcrum, a resistive force (or load), and an applied force (or effort). There are three classes of levers which describe different configurations of those key lever system components (First, second, and third-class levers).
- Mass: Mass is measured in kilograms (kg) and is the amount of matter in something. A person’s mass consists of all the materials that make up their given body and can also include anything connected to or layered on top of their body.
- Maximum force: Refers to an individual exerting maximum effort when completing a physical task using their full range of motion with appropriate sequencing.
- Momentum: The motion of an object that is related to its mass and velocity.
- Normal Force: Acts upward and is opposite to the force of gravity.
- Range of motion (ROM): The measure through which a joint moves through its full movement potential, or the movement at a joint from a position of full flexion to full extension.
- Resistive Force (Load): Force acting to prevent motion.
- Sequencing of joint rotation: Refers to the idea that when attempting to achieve maximum force, the best possible strategy is to use joints specifically from large to small. What this means is rotating and utilizing joints which activate large muscles before moving onto small joints and muscles.
- Stability: The ability of an object to maintain or return to a position of equilibrium when acted upon by external forces.
- Velocity: The rate at which an object is moving over time.
- Weight: The measure of gravitation or gravitational pull on an object, which can be calculated using both gravity and mass.
OpenAI. (2025). ChatGPT. [Large language model]. https://chat.openai.com/chat. Prompt: List the key terms and their definitions in the content provided.
