Biomechanics of Training

Biomechanics Importance

• Biomechanics: Study of biological systems using mechanics.
• Applies to movement analysis, tissue properties, and device manufacturing.
• Underpins practical problems faced by strength and conditioning (S&C) coaches.

Fundamentals of Classical Mechanics

• Force is a fundamental quality.
• Force: A pushing/pulling action that changes a body's motion.
• Newton's Second Law: $F = ma$, where:
  • $F$ = force (vector)
  • $m$ = mass (scalar)
  • $a$ = acceleration (vector)
• Movement analysis requires understanding forces causing accelerations.

Rate of Force Development (RFD)

• RFD: Rate of change of force with respect to time. Instantaneous RFD: $RFD = \frac{dF}{dt}$.
• Approximation: $RFD = \frac{DF}{Dt}$.
• Verkhoshansky's RFD types:
  • Explosive strength (E): RFD over the entire time to reach max force; $E = \frac{F<em>{max}}{t</em>{F_{max}}}$.
  • Starting strength (Q): RFD until half max force is reached; $Q = \frac{F<em>{\frac{1}{2}max}}{t</em>{F_{\frac{1}{2}max}}}$.
  • Acceleration strength (G): RFD from half max to max force; $G = \frac{F<em>{max} - F</em>{\frac{1}{2}max}}{t<em>{F</em>{max}} - t<em>{F</em>{\frac{1}{2}max}}}$.

Importance of RFD

• High RFD allows greater force during sports skills due to short time availability.
• Reactive Strength Index (RSI) as a proxy for RFD during landing:
  • $RSI = \frac{jump height}{ground contact time}$

Defining Strength

• Strength: Ability to voluntarily apply force under specified constraints.
• Influenced by functional tissues, anthropometrics, motor control, and motivation.

Defining Robustness

• Robustness: Tissue tolerance to forces during sports participation.
• Involves tissue quality and movement mechanics.

Defining Efficiency

• Efficiency in endurance: Capacity to repeatedly express force cyclically for sustained periods.
• Reducing metabolic cost and optimizing movement mechanics are crucial.

Work, Energy, and Power

• Mechanical work (W): $W = \int Fdx$.
• Simplified: $W = F \cdot x$ (if force is constant and in one direction).
• Work-energy relationship: Work done equals change in kinetic and potential energy.

Kinetic and Potential Energy

• Kinetic energy: Energy due to motion; $\frac{1}{2}mv^2$.
• Potential energy: Stored energy due to height; $mgh$.
• Conservation of energy: Total energy in a closed system remains constant.

Power

• Mechanical power (P): Rate of doing work; $P = \frac{dW}{dt}$.
• If force is constant: $P = F \cdot v$.

Impulse and Momentum

• Impulse (I): Integral of force with respect to time; $I = \int Fdt$.
• Impulse-momentum relationship: Impulse equals change in momentum; $I = m(v<em>1 - v</em>0)$.

Newton's Laws

• Law 1: A body remains at rest or in uniform motion unless acted upon by a force.
• Law 2: Change in motion is proportional to force; $F = ma$.
• Law 3: For every action, there is an equal and opposite reaction.

Forces in Sports

• Inertia: Resistance of mass to acceleration.
• Gravity: Constant downward vertical acceleration.
• Reaction Forces: Forces imparted back on the athlete when applying force to an external mass.
• Friction: Necessary for horizontal forces, acceleration, and stability.
• Fluid Forces: Hydrodynamic and aerodynamic forces (drag, lift).

Gross Anatomy and Body Position

• Muscular System: Dissipates/transfers energy, does work, maintains tension, stores/returns elastic energy.
• Contraction Types:
  • Concentric: Muscle shortens (least efficient).
  • Eccentric: Muscle lengthens (most structural damage).
  • Isometric: Muscle length constant (least ATP use).

Levers

• Lever System: Pivot/fulcrum with a rigid body.
• Torque (T): Tendency of a force to create rotation; $T = r \times F$ or $T = Fd$.
  • Where r is the vector from the pivot to the point of force.
  • Where d is the perpendicular distance between the force and the pivot.
• Lever classes: First, second, and third class, each amplifying force or range of motion differently.

Muscles to Movement

• Outcome force production is interdependent and complex.
• The system is flexible in its ability to cope with changes in functional capacity.
• Available structure sets up a motor outcome domain.
• The system has self-stabilizing properties that potentially simplify movement control.
• Force around a joint can be affected by muscles that do not cross that joint.
• Steering might be key.
• Athletes are limited in their ability to generate accelerations through movements by both geometric and anatomical constraints.

Fine Anatomy and Architecture

• Force-Time Relationship: Delay between signal and force development.
• Force-Length Relationship: Inverted U, optimal length has adequate binding sites and space to shorten.
• Force-Velocity Relationship: Velocity restricts achievable force.
• Parallel arrangement allows direct summation of forces, leading to much higher overall force production and is restricted to an absolute length change equal to that of a single unit.
• Fibre Pennation: The degree to which muscle fbres are oriented obliquely relative to the line of pull of the muscle. Increased pennation force potential, limiting the increase in muscle thickness.

Dynamic Correspondence

• Dynamic Correspondence: Similarity between training activities and sport skills.
• Criterion 1: The Amplitude and Direction of Joint Movements
• Criterion 2: The Most Important Region of Force Production
• Criterion 3: The Applied Effort
• Criterion 4: The Time Available
• Criterion 5: The Type of Muscular Work
• Criterion 6: The Multi-Joint Movement Strategy (Includes Limb Steering/Control and Energy Transfer Issues)