Motor Units and Force Production

Muscle Fiber and Motor Units

• Linkage to Nervous System: Muscle functions are closely tied to the nervous system.
• Passive Tension: Refers to elastic tension generated by connective tissue (e.g., epimysium, perimysium, tendon).

Motor Unit

• Definition: Comprises an alpha motor neuron and all muscle fibers it innervates.
• Activation: Firing is all-or-none; all fibers in a motor unit contract together.

Motor Unit Size and Control

• Smaller Motor Units: Facilitate fine motor skills for tasks like hand and eye coordination.
• Larger Motor Units: Produce greater force for gross motor activities such as running or jumping.

Types of Muscle Fibers

• Slow-Twitch (Type I): High fatigue resistance; lower force, slower contraction speed.
• Fast-Twitch (Type IIa): Intermediate fatigue resistance; moderate force and speed.
• Fast-Twitch (Type IIb): Low fatigue resistance; high force and rapid contraction speed.

Motor Recruitment and Force Production

• Size Principle: Motor units are recruited from smallest to largest based on force needs, enhancing movement efficiency.
• Spatial Summation: Multiple motor units can collectively produce smooth, coordinated movements.
• Rate Coding: Increased frequency of motor unit firing enhances force production through temporal summation.

Cross Activation

• Activating one hemisphere of the brain can influence movements in the opposite limb, with transfer magnitude reliant on limb proficiency.

Refractory Period and Neural Control

• Relative Refractory Period: A phase when a stronger stimulus is necessary to generate an action potential, affecting preparation for movement.
• Primary Motor Cortex (M1): Key brain region for initiation and execution of voluntary movement commands.

Neural Transmission

• Basal Ganglia Role: Involved in the coordination and modulation of movement, ensuring a smooth flow of motor commands.

Sensory and Motor Pathways

• Sensory Pathways: Ascending tracts for proprioception (dorsal column) and pain/temperature (spinothalamic tract).
• Motor Pathways: Descending tracts for fine motor control (corticospinal tract) and reflexes/postural control (brainstem/extrapyramidal system).

Feedback Mechanisms

• Closed-loop Feedback: Involves adjustments based on real-time information during task performance.
• Open-loop Control: Movements are executed without real-time feedback, aiming for accuracy.

Cognition and Movement

• Cognitive Processing: Involves mental functions that lead to understanding and acquiring knowledge, impacting movement and learning adjustments.### Motor Learning
• Motor skill involves voluntary, goal-directed activities learned through practice and experience.
• Characteristics of motor skills: goal-directed, voluntary, learned, require body movement.

Interaction of Constraints

• Involves environmental, task-related, and individual constraints that affect motor skill performance.
• The interaction among these constraints informs curriculum design and talent identification.

Perception-Action Coupling

• Refers to the relationship between movement and environmental affordances that influence skill execution.
• Skilled performers effectively utilize perceived affordances to inform their actions.

Types of Motor Skills

• Fundamental Motor Skills: Provide the foundation for specialized motor skills.
• Locomotor Skills: Movement through space (e.g., crawling, walking).
• Manipulative Skills: Control of objects (e.g., throwing, catching).

Affordances

• Opportunities for action based on the individual's capabilities.
• High affordance examples: walking, running, which allow for consistent goal achievement.
• Low affordance examples: rock climbing and complex dance routines, requiring adaptability and energy efficiency.

Skills and Action Perception

• Action performance is influenced by perceived affordances, with inherited traits impacting skill execution.
• Abilities that influence performance include hand-eye coordination, reaction time, and strength.

Skill Classification

• Skills are categorized based on:
  • Discrete Skills: Clear beginning and end with one distinct movement.
  • Serial Skills: A series of discrete movements performed in a sequence.
  • Continuous Skills: No clear beginning or end, often repetitive (e.g., swimming).

Motor Behavior Domains

• Motor Learning: Individuals acquire motor skills through practice.
• Motor Control: Influenced by the environment being either stable or variable.
• Motor Development: Growth of motor skills influenced by physical and cognitive development.

Environment Types

• Closed Environment: Stable and predictable setting where movement can be performed in a consistent manner.
• Open Environment: Unpredictable setting requiring rapid adaptation and responsiveness to changes.