The Physiology of Training: Effects of Aerobic and Anaerobic Training

The Physiology of Training: Effects of Aerobic and Anaerobic Training

Overview

• Presentation prepared by:

  • Scott K. Powers, Ph.D., Ed.D.

  • Edward T. Howley, Ph.D.

  • John Quindry, PhD.

• Source: Exercise Physiology: Theory and Application to Fitness and Performance, 11th Edition.

• Copyrights: 2021 McGraw-Hill Education, all rights reserved.

Lecture Outline

• Principles of Training

• Endurance Training and VO2 Max

• Why Does Exercise Training Improve VO2 Max?

• Endurance Training: Effects on Performance and Homeostasis

• Molecular Bases of Exercise Training Adaptation

• Signaling Events Leading to Endurance Training-Induced Muscle Adaptation

• Endurance Training: Links Between Muscle and Systemic Physiology

• Detraining Following Endurance Training

• Muscle Adaptations to Anaerobic Exercise Training

Principles of Training

Overload (FITT Principle)

• Training effect occurs when a physiological system is exercised at a level beyond which it is normally accustomed.

Specificity

• Training effect is specific to:

  • Muscle fibers recruited during exercise.

  • Energy systems involved (aerobic vs. anaerobic).

  • Velocity of contraction.

  • Type of contraction (eccentric, concentric, isometric).

Reversibility

• Gains are lost when training ceases.

Principle of Specificity

• Example study referenced (not in the book):

  • Swam 3 days/week for 1 hour over 10 weeks.

  • VO2max was assessed on treadmill running and tethered swimming.

Endurance Training and VO2 Max

Training to Increase VO2 Max

• Requires engagement of large muscle groups and dynamic activity for a duration of 20–60 minutes, at least 3 times per week, at an intensity of ≥50% VO2 max.

Increases in VO2 Max with Endurance Training

• Average increase: 15–20%.

• Smaller increases for individuals with a high initial VO2 max; may require higher intensities (>70% VO2 max) for improvements.

• Up to 50% improvement in those with a low initial VO2 max.

Heritability (Genetics)

• Determines approximately 50% of VO2 max in sedentary adults.

• Genetics significantly influences the training response.

  • Average improvement in VO2 max: 15-20%.

  • Low responders improve by only 2-3%.

  • High responders can improve VO2 max by approximately 50% with rigorous training.

Variability in Muscle Size and Strength Gains

• Study assessed variability in muscle size and strength changes after unilateral resistance training among men and women.

Data Summaries

• Changes in muscle size and strength recorded:

  • Men experienced a muscle size change from 22.2 ± 0.4 cm to 22.4 ± 0.3 cm (difference: 0.2).

  • Women experienced changes from 14.0 ± 0.2 cm to 14.2 ± 0.2 cm (difference: 0.2).

  • 1RM strength average before training: 8.5 ± 0.2 vs. post-training: 12.4 ± 0.2.

  • For men: pre-training: 11.7 ± 0.2 vs. post-training: 15.9 ± 0.2 (difference: 4.3).

  • For women: pre-training: 6.2 ± 0.1 vs. post-training: 9.9 ± 0.1 (difference: 3.6).

VO2 Max

Defined by the Fick Equation

• $VO2_{max} = maximal ext{ cardiac output} imes a-vO2 ext{ diff}$

Differences in VO2 Max Between Individuals

• Primarily due to differences in stroke volume (SV) max.

Exercise-Induced Improvements in VO2 Max

• Short duration training (approx. 4 months): Increases SV is a dominant factor for improving VO2 max.

• Longer duration training (~28 months): Both SV and a-vO2 contribute to VO2 max enhancements.

Training Increases Maximal Stroke Volume

• Filling of the ventricles increases ( EDV), which leads to:

  • Increased plasma volume.

  • Enhanced venous return.

  • Increased ventricular volume.

  • Decreased total peripheral resistance.

  • Decreased arterial constriction.

  • Maximal muscle blood flow without changes in mean arterial pressure.

  • Increased contractility of the heart.

Training-Induced Changes

• Changes can occur rapidly (about 6 days) with the following initial increases:

  • 11% increase in plasma volume.

  • 7% increase in VO2 max.

  • 10% increase in stroke volume.

Muscle Blood Flow and Utilization of Oxygen

• Improved ability of muscle fibers to extract and utilize O2 from the blood involves:

  • Increased capillary density (angiogenesis).

  • Slower blood flow through muscle increases the time for O2 diffusion.

  • Increased mitochondrial number and density improves capacity for oxidative phosphorylation.

• More ADP transporters enhance ATP production at mitochondria, leading to decreased lactate and H+ formation, and less phosphocreatine (PC) depletion.

Endurance Training Increases Arteriovenous O2 Difference

• As a result of enhanced oxygen extraction capabilities.

Endurance Training and Mitochondrial Dynamics

• Increased mitochondrial volume positively correlates with cytosolic ADP concentration during submaximal exercise.

• Endurance exercise training reduces the O2 deficit at the onset of physical activity.

Exercise Effects on Metabolism

Fat and Glucose Metabolism

• Endurance exercise training increases fat metabolism while decreasing glucose metabolism during submaximal exercise.

• This shift is known as the crossover point, which moves to the right, indicating an increased fat utilization relative to carbohydrates.

Antioxidant Capacity

• Endurance training improves the antioxidant capacity of muscles.

  • Contracting skeletal muscles produce free radicals, contributing to oxidative damage and muscle fatigue.

  • Training enhances the activity of endogenous antioxidant enzymes, facilitating the removal of free radicals and protecting against exercise-induced oxidative damage.

Acid-Base Balance Improvement

• Endurance training enhances acid-base balance during exercise.

Training Adaptation: The Big Picture

Protein Synthesis

• Endurance and resistance training promotes protein synthesis in muscle fibers.

  • “Stress” from exercise activates gene transcription.

  • mRNA levels typically peak within 4–8 hours post-exercise and return to baseline within 24 hours.

• A single exercise bout does not lead to significant protein changes within muscle fibers; adaptation requires repeated training over time.

Time Course of Changes in Muscle Following Training

• 36 weeks of structured endurance training shows progression of VO2 max and anaerobic threshold changes.

• Data illustrates regular adaptations:

  • Before training VO2 max: 32.2 ± 2.2 ml min kg,

  • After 12 weeks: 51.3 ± 2.5 ml min kg,

  • After 24 weeks: 40.3 ± 2.4 ml min kg,

  • After 36 weeks: 42.3 ± 2.9 ml min kg.

MicroRNAs (miRNAs)

• Small molecules that inhibit protein synthesis by blocking mRNA action.

• There are over 700 miRNAs in humans; endurance and resistance training can reduce levels of various miRNAs.

• Decreases in specific miRNAs may contribute to exercise-induced training responses.

Signaling Pathways in Exercise-Induced Adaptation

Primary and Secondary Pathways

• Primary signals that lead to muscle adaptations include:

  • Mechanical stretch (from resistance training).

  • Calcium (from endurance training).

  • AMP/ATP ratio (from endurance training).

  • Free radicals (from endurance training).

Adaptations Influence Physiological Responses to Exercise

• Effects on the sympathetic nervous system (decreased E/NE levels) and cardiorespiratory responses (lower heart rate and ventilation).

• One-leg training studies indicate that training effects do not transfer between legs, indicating muscle-specific adaptation.

Detraining Effects on VO2 Max

• Rapid decline in VO2 max:

  • Decrease of about 8% within 12 days and up to 20% after 84 days.

  • Initial drop attributed to reduced stroke volume, later decreases in a-vO2 max.

Mitochondrial Adaptations and Detraining

• Muscle mitochondria can double within the first 5 weeks of endurance training.

• Adaptations can be quickly lost with detraining, with 50% of training gains lost within one week.

• Requires 3-4 weeks of retraining to regain mitochondrial levels.

Anaerobic Exercise Characteristics

• Refers to high-intensity, short-duration exercise (10-30 seconds).

• Engages both type I and II muscle fibers.

• Energy sources:

  • For <10 seconds: ATP-PC system primarily.

  • For 20-30 seconds: 80% anaerobic, 20% aerobic.

Muscle Adaptations to Anaerobic Training

• Sprint training for 4-10 weeks can increase peak anaerobic power by 3-28%.

• Enhancements in muscle buffering capacity, including intracellular buffers and hydrogen ion transporters.

• Hypertrophy of type II muscle fibers and elevation of enzymes linked to ATP-PC system and glycolysis.

• High-intensity interval training promotes mitochondrial biogenesis, particularly for sessions exceeding 30 seconds at near or above VO2 max.

Lecture Summary

• The lecture covered the principles of training, effects of endurance training on VO2 max, improvements in performance due to exercise training, underlying molecular mechanisms of adaptation, signaling pathways involved, systemic physiology links, effects of detraining, and adaptations to anaerobic exercise training.

• These findings reflect on the interconnectedness of physiological responses to structured training regimens, enhancing fitness and performance.