Study Notes on Body Mechanics, Energy, and Kinetics

Body Mechanics in Walking and Running

  • Basic Movement Dynamics

    • Plant the legs; body mass moves over a fixed point.

    • When the body passes the line of gravity, it enters a falling position.

    • The need to 'catch ourselves' central to understanding walking and running.

    • Walking described as a 'controlled fall' due to the body mass positioning.

  • Conservation of Momentum

    • Emphasizes the relationship between two main positions in walking.

    • Work done on one leg must counterbalance work on the other, equating to zero net work to satisfy conservation of momentum.

    • Introduces concept relevant in physics—momentum: ( m1 v1 + m2 v2 = 0 ) where mass and velocity are conserved in a closed system.

  • Running Mechanics

    • Distinction made between walking (fixed point) and running (open point) where flight dynamics become relevant.

    • Discussed flight phase in running where body undergoes a significant change in momentum and position.

  • Relative Angles in Walking

    • Reciprocal motions and angles formed by the legs must equal zero for momentum conservation.

    • Back swing of one leg counters the forward swing of the other to maintain balance and forward progress.

  • Kinetic Chain Dynamics

    • The kinetic chain can initiate at different segments.

    • For broad jumps, analyzing which body part moves first (head, shoulders, trunk).

    • Importance of head movement initiating momentum: "You move your head first to generate forward mass and velocity."

    • Arms move last; their acceleration aids in balance and rotational energy creation.

  • Integrated body movement

    • Each segment's stopping point needs synchronization for effective propulsion.

    • Misalignment in stop timing can impede forward momentum thereby reducing jump and running efficiency.

    • Full backward and forward swings must balance each other to maximize propulsion.

Energy Expenditure in Gait

  • Energy Minimization in Walking

    • Walking occurs at various speeds with an emphasis on minimizing energy expenditure.

    • One foot always on the ground inherently slows down movement; solutions sought for optimizing speed efficiency.

  • Graphs of Power and Speed

    • Power vs. speed graph demonstrates energy costs of walking versus running.

    • Physiological costs mainly responsible for energy increases at higher speeds, while biomechanical factors become controllable areas of efficiency.

  • Walk vs. Run Dynamics

    • Key differences in gait observed between walking and running.

    • Natural gait variation due to body structure and limb sizes; goal to find an optimum speed for energy used vs. distance covered.

Principles of Kinetics and Kinematics

  • Kinetics vs. Kinematics

    • Kinematics: description of motion without mass consideration.

    • Kinetics: focus on mass in relation to forces at play.

  • Definition of Force

    • Force defined as action exerted by one object onto another; understood through Newton’s laws.

    • Energy viewed as movement; linking force and energy, energy defined in terms of ATP energy storage and transfer.

  • Types of Forces

    • Conservative Forces: Path independent forces; gravitational force acts between two masses consistently.

    • Non-Conservative Forces: Dependent on path; many biomechanical forces fall into this category.

  • Impact of Gravity on Energy

    • Weight defined as ( m \times g ) where ( g ) is gravitational acceleration (approximately 9.8 m/s²).

    • Weight variations based on body mass have significant implications for sports performance.

  • Normal Force

    • Always acts at a right angle to the surface; role changes with surface incline.

    • Normal force decreases when climbing slopes; affects body biomechanics significantly during movement.

  • Real-World Applications

    • Insight into mountain climbing behavior: climbers use physical imperfections to counteract necessary forces to ascend vertical spaces.