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Levers and Movement Flashcards

Producing Movement

Levers

  • For movement to occur, the musculoskeletal system uses leverage.
  • Leverage: Action or advantage of using a lever.
  • Lever: Refers to a rigid structure that rotates around a fixed point.
  • Levers allow for the application of increased ‘force’ and/or ‘speed’.
  • Examples of everyday levers exist.

Classification of Levers

  • A lever's class is determined by the location of the axis, force, and resistance in relation to each other.
  • There are 3 classes: 1st, 2nd, and 3rd class.
  • Most levers in the human body are third-class levers and will be the focus of this subtopic.
    • First-Class Levers: The axis (fulcrum) is located between the force and the resistance. An example of this is scissors or a seesaw; in the human body, an example is tilting the head back where the neck muscles provide the force, the weight of the head is the resistance, and the joint between the skull and spine is the axis.
    • Second-Class Levers: The resistance is between the axis and the force. Examples include a wheelbarrow; in the body, an example is a calf raise where the ball of the foot is the axis, the body weight is the resistance, and the calf muscle contracting is the force.
    • Third-Class Levers: The force is applied between the axis and the resistance. Examples include using a shovel; in the body, the biceps curl where the elbow joint is the axis, the weight in the hand is the resistance, and the biceps muscle contracting is the force.

Components of a Lever

  • Axis: The joint in the body that the lever moves around.
  • Force: The muscles that contract to generate the force to move the lever.
  • Resistance: The bone of the body and whatever is being held or moved by the bone.

Third-Class Levers

  • Bones act as levers and work with the muscles to create movement.
  • Bones create attachment points for the muscle.
  • When a muscle contracts, the origin (fixed point) and insertion (moveable point) are drawn together.
  • The muscle pulls on the bone at the insertion point attached across a joint, producing movement in a specific direction.
  • The force (muscular effort) is applied between the axis (joint) and the resistance (bone and/or equipment to be moved).
    • Third-class levers are the most common type in the human body because they allow for a greater range of motion and speed, although they require more force compared to other lever systems.

Soccer Player Example

When a soccer player kicks a ball:

  1. Axis: The knee joint (or sometimes the hip joint), acting as the pivot point.
  2. Force: The muscular force exerted by the quadriceps and hamstrings to extend the lower leg.
  3. Resistance: The weight of the lower leg and foot, as well as the ball being kicked.
  • The force is applied between the axis (knee joint) and the resistance (ball).
  • This configuration allows for high-speed movements and a large range of motion, which is ideal for creating fast and powerful kicks in soccer.
  • The ball is the resistance.
    • Additional Details: The precise coordination and timing of muscle contractions are crucial for optimizing the force and accuracy of the kick. Factors such as the angle of the knee joint, the point of contact with the ball, and the follow-through motion all contribute to the