Physiology of Training Part 1

Physiology of Training Part 1

Learning Objectives

• Explain the basic principles of training.
• Discuss the role genetics plays in determining \dot{V}O_{2max}.
• Describe the typical change in \dot{V}O_{2max} with endurance training.
• Describe the training-induced physiological adaptations that lead to an increased \dot{V}O_{2max}.
• List and discuss the primary changes that occur in skeletal muscle as a result of endurance training.

Principles of Training

• Regular exercise leads to adaptations that reduce the disruption of the internal environment during exercise.
• Endurance training and resistance training are two types of exercise.
• The principles of training include:
  • Progressive Overload
  • Specificity
  • Reversibility
  • An organ system (cardiovascular) or tissue (skeletal muscle) must be exercised at a level beyond which it is accustomed to achieve a training adaptation.

Principle of Progressive Overload Training (Overload)

• Adaptations occur in three main areas:
  • Morphological
  • Metabolic
  • Neuromuscular

Principles of Specificity

• Training adaptations are highly specific to the type of activity being performed and the volume and intensity of the exercise.
• The training program must stress the physiological systems that are critical for optimal performance in a given activity to achieve specific training adaptations and goals.
• Training may be specific to:
  • Muscles involved
  • Fiber types recruited
  • Principal energy system involved
  • Velocity of contraction
  • Type of muscle contraction

Principles of Reversibility

• Fitness gains from exercising are quickly lost when training stops (detraining).
• Physiological adaptations will be reversed.

Training Programs and Changes in \dot{V}O_{2max}

• Endurance training programs:
  • 20 to 60 min at >50% \dot{V}O_{2max}, 3+ sessions per week
  • HIT training (30 s all-out efforts)
• Typical \dot{V}O_{2max} increases with training:
  • 2 to 3 month program = 15–20% increase in \dot{V}O_{2max}
  • Initial level may influence required training intensity
    • Low initial \dot{V}O{2max} intensity 40% \dot{V}O{2max}
    • High initial \dot{V}O{2max} intensity >70% \dot{V}O{2max}

Impact of Genetics on \dot{V}O_{2max} and Individual Responses

• Genetics plays an important role in determining \dot{V}O_{2max}.
  • Heritability determines 50% of \dot{V}O_{2max} in untrained subjects.
• Genetics plays a key role in determining how individuals respond to training.
  • Average improvement is 15-20%.
  • Low responders to training achieve only 2-3% improvement.
  • High responders to training achieve up to 50% improvement.
  • Heritability of training-induced change in \dot{V}O_{2max} is 47%.
  • 21 different genes play a role in changes in \dot{V}O_{2max} with training.

Why Does Exercise Training Improve \dot{V}O_{2max}?

• \dot{V}O2 \text{ mL} \cdot \text{min}^{-1} = \dot{Q} \times a-vO2 \text{ difference}
• \dot{V}O{2max} \text{ mL} \cdot \text{min}^{-1} = \text{Maximal } \dot{Q} \times \text{maximal } a-vO2 \text{ difference}
• \dot{Q} = HR \times SV

Stroke Volume

• Can occur rapidly

• Can occur with prolonged training

• \dot{Q} \text{ (L} \cdot \text{min}^{-1}) = SV \text{ (mL} \cdot \text{beat}) \times HR \text{ (bpm)}
  Untrained male: 72 \times 70 = 5.00
  Trained male: 50 \times 100 = 5.00
  Untrained female: 75 \times 60 = 4.50
  Trained female: 55 \times 80 = 4.50

• Cardiac contractility – Strength of cardiac muscle contraction when EDV, afterload and HR remain constant

  • HIT increases cardiac pumping by increasing the force of ventricular contraction (animal studies)
  • Endurance training can increase ventricular “twist mechanics” and increase SV (human studies)

• Endurance training results in a decrease in afterload

• Increase in maximal muscle blood flow

• Increase in maximal \dot{Q} results in unchanged MAP

Factors Contributing to Training-induced Increases in VO2max

• Increased \dot{V}O_{2max} is influenced by:
  • Maximal cardiac output
    • Stroke volume
      • Preload
      • Afterload
      • Sympathetic nervous system activity to working muscle
  • a-v O2 difference
    • Muscle blood flow
    • Capillaries
    • Mitochondria