Unit 1

1. Key Definitions and Related Fields

  • Development: A continuous, sequential, orderly, and irreversible process of change in functional capacity related to age. It includes cognitive, social, and motor domains.

  • Motor Development: Continuous change in movement abilities and the underlying factors driving those changes.

  • Related Areas of Study:

    • Motor Learning: Relatively permanent gains in motor skill capability associated with practice or experience.

    • Motor Control: The neural, physical, and behavioral aspects of movement.

    • Motor Behavior: Broad field encompassing both motor learning and motor development.

  • Related Terms:

    • Physical Growth: Quantitative increase in size or body mass.

    • Physical Maturation: Qualitative advance in biological makeup (cellular, organ, or system level).

    • Aging: Process occurring with the passage of time leading to loss of adaptability or full function, eventually leading to death.

  • Key Stakeholders: Educators (best practices), Therapists (movement factors), Engineers/Designers (living spaces/equipment), Health Care Providers (early movement impact on long-term health).

2. Newell's Model of Constraints

Constraints shape, limit, encourage, or channel movement behaviors. Development occurs through the interaction of three categories of constraints:

  1. Individual Constraints: Internal characteristics unique to the person.

    • Structural: Related to physical body structure (e.g., height, muscle mass).

    • Functional: Related to behavioral or psychological function (e.g., attention, motivation, fear).

  2. Environmental Constraints: External global properties of the environment (not task-specific).

    • Physical: Environmental factors such as gravity, surface texture, temperature, or lighting.

    • Sociocultural: Social and cultural expectations, such as gender roles or cultural movement norms.

  3. Task Constraints: External requirements specific to a particular task or skill.

    • Includes task goals, specific rules guiding performance, and required equipment.

Note on Atypical Development: Differences in individual structural or functional constraints can alter developmental trajectories, causing development to be advanced or delayed relative to typical population averages.

3. Observing Developmental Change and Research Methods

  • Developmental Trajectories: Curves plotting behavior capability over time or age.

    • Proficiency Barrier (Seefeldt, 1980): A threshold of fundamental movement skills; if not crossed by a certain age, subsequent complex motor skill development becomes significantly more difficult.

  • Research Designs:

    • Longitudinal: The same individual or group is observed performing over an extended period. Directly observes change.

    • Cross-Sectional: Individuals or groups of different ages are observed at one point in time. Infers change rather than directly observing it.

    • Meta-Analysis: Statistical technique combining results across multiple studies to compute a generalizable effect size.

    • Review Paper: Qualitative comparison and contrast of multiple studies on a given topic.

  • Developmental Paradox:

    • Universality: Members of a species display broad structural and movement similarities across development.

    • Variability: Individual differences exist at every stage of development.

4. Theoretical Perspectives in Motor Development

  1. Maturational Perspective (1930s–1950s):

    • Core Idea: Development is driven by an internal biological clock and central nervous system (CNS) maturation.

    • Key Figures: Arnold Gesell (twin studies, biological timeline), Myrtle McGraw (studied twins in different environments to explore nature vs. nurture).

    • Principles: Environment can speed up or slow down development temporarily, but cannot alter the genetically predetermined timeline.

  2. Normative & Biomechanical Descriptive Perspectives (1950s):

    • Normative Descriptive: Led by Espenschade, Glassow, and Rarick. Focuses on standardized quantitative performance scores (e.g., outcome scores in running distance, throw speed).

    • Biomechanical Descriptive: Led by Glassow and Halverson. Focuses on sequential, qualitative biomechanical changes in movement patterns over time.

  3. Information Processing Perspective (1960s–1980s):

    • Core Idea: The brain acts like a computer, processing sensory input, executing decisions, and outputting motor commands.

    • Focus: Environment-driven learning (nurture), memory, attention, response selection, and feedback mechanisms.

  4. Ecological Perspective (1980s–Present):

    • Stresses the continuous dynamic interplay between the individual, environment, and task. Motor control is distributed throughout the system rather than solely controlled by the CNS.

    • Dynamical Systems Approach:

      • Movement is "softly assembled" and self-organizing based on interacting constraints.

      • Rate Limiter / Rate Controller: An individual system or constraint that holds back or slows the development of a motor skill until it reaches a critical threshold.

    • Perception-Action Approach (Gibson):

      • Perceptual and motor systems evolve together dynamically.

      • Affordances: The function or action possibilities an object or environment offers to an individual based on their capabilities.

      • Body Scaling: Adapting environment or equipment dimensions to match the physical dimensions of the individual actor.

5. Biomechanical Principles of Motion and Stability

  • Newton's First Law of Motion:

    • An object at rest stays at rest, and an object in motion stays in motion, unless acted upon by an external force.

    • Inertia: Resistance to motion, directly proportional to mass.

    • Momentum: Product of mass and velocity (p=m×vp = m \times v).

  • Newton's Second Law of Motion:

    • Acceleration (aa) is directly proportional to the applied force (FF) and inversely proportional to mass (mm):     F=m×aF = m \times a     a=Fma = \frac{F}{m}

  • Optimizing Performance:

    • Extending Force Distance: Increasing linear distance (e.g., stepping forward) or angular range of motion (e.g., rotary prep position) increases velocity at release.

    • Rotating Limbs: Object velocity depends on limb rotational speed and limb length at the point of release. Bending the arm reduces inertia, allowing faster angular acceleration prior to extension.

    • Open Kinetic Chain: A timed sequence of body segment movements where force generated by lower segments transfers to higher segments in optimal timing.

    • Force Absorption: To decrease impact forces, land or catch by increasing the time and physical distance over which force is absorbed (e.g., bending knees upon landing).

  • Stability and Balance:

    • Stability: Resistance to disruption of movement. Increased by broadening the base of support and lowering the center of gravity.

    • Balance: Ability of an object or person to maintain equilibrium.

    • Stability-Mobility Trade-Off: Maximizing stability reduces mobility; developing movers must transition from high-stability strategies to mobility strategies to increase speed and performance.

6. Systemic Observation and Skill Analysis

Practitioners can systematically analyze movement using five steps:

  1. Observe the complete skill.

  2. Analyze each phase of movement.

  3. Use biomechanical knowledge in the analysis.

  4. Select specific mechanical errors to be corrected.

  5. Decide on appropriate instructional strategies to correct errors.