resistance training

Physiology of Resistance Training

Authors and Context

  • Authors: Scott K. Powers, Ph.D., Ed.D., Edward T. Howley, Ph.D., John Quindry, Ph.D.
  • Textbook: EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 11th Edition
  • Copyright: © 2021 McGraw-Hill Education. All rights reserved.

Lecture Outline

  • Physiological Effects of Strength Training
  • Resistance Training Changes in the Nervous System
  • Time Course and Signaling Events of Muscle Growth
  • Muscle Protein Synthesis Timing
  • Satellite Cells Role in Hypertrophy
  • Detraining Effects
  • Concurrent Strength and Endurance Training

Physiological Effects of Strength Training

  • Muscular Strength:

    • Definition: Maximal force that a muscle group can generate.
    • Measurement: 1 repetition maximum (1-RM).

  • Muscular Endurance:

    • Definition: Ability to make repeated contractions against a submaximal load.

  • Strength Training:

    • High-resistance training: 6–10 reps till fatigue, leads to strength increases.
    • Low-resistance training: 35-40 reps till fatigue, leads to increases in endurance.

Neural Adaptations Responsible for Early Gains in Strength

  • Initial strength gains: Primarily from nervous system adaptations during the first 8 weeks of training.
  • Evidence for neural adaptations:
    • Increase in muscular strength within the first two weeks without an increase in muscle fiber size.
    • The phenomenon of cross-education: Training in one limb improves strength in the untrained limb.
    • Removing the central nervous system results in reduced strength gains.

Changes in the Nervous System Due to Resistance Training

  • Notable adaptations include:
    • Increased Neural Drive: Enhanced signal transmission from the brain to muscles.
    • GTO Desensitization: Decreased sensitivity of the Golgi tendon organs (GTO), reducing inhibitory effects on muscle contraction.
    • Motor Unit Recruitment: Increased number of motor units activated during contractions.
    • Motor Unit Firing Rate: Enhanced synchronization and frequency of motor unit firing.
    • Neural Transmission: Improved conduction across the neuromuscular junction, characterized by more synaptic vesicles and receptors.

Changes in Peripheral Skeletal Muscle and Force Production

  • Modifications include:
    • Increased specific force production due to enhanced calcium sensitivity, increasing actin and myosin binding (fiber strength up by 17.5%, fiber size up by 6.7%).
    • Muscle Hypertrophy: Increase in fiber size is considered the primary factor.
    • Muscle Hyperplasia: Increase in fiber number, though its occurrence in humans is unclear.

Time Course of Resistance Training-Induced Muscle Protein Synthesis

  • Diminishing Returns:
    • Protein synthesis and resistance exercise can only stimulate protein synthesis to a certain extent, requiring a refractory period before restimulation.
    • Amino acids: Maximum stimulation occurs around 4 hours post-intake.
    • Resistance exercise: Duration required for maximum stimulation remains unknown.

Anabolic Resistance in Aging Individuals

  • Anabolic Resistance: Reduced capacity of older individuals to gain muscle hypertrophy and strength compared to younger individuals following resistance training.
    • Characterized by lower sensitivities to protein intake and resistance exercise.

Key Factors in Resistance Training-Induced Muscle Protein Synthesis

  • mRNA Increases: Lead to protein synthesis at the ribosome level after resistance training.
    • Increased Ribosomes: Number increases, enhancing muscle protein synthesis capacity (translational efficiency).
    • mTOR Activation: The protein kinase mechanistic target of rapamycin (mTOR) is critical for accelerating protein synthesis post-resistance training.

Role of Satellite Cells in Hypertrophy

  • Satellite Cells: Stem cells that lie between the sarcolemma and basal lamina of muscle fibers.
    • Resistance training activates these cells, leading to division and fusion with adjacent muscle fibers, increasing myonuclei.
    • Increased myonuclei ratio is essential for accommodating larger muscle fiber sizes, sustaining protein synthesis for maximal hypertrophy.
    • Activation of these cells can be diminished in older individuals, limiting hypertrophy potential.

Detraining Following Strength Training

  • Cessation of Training: Leads to muscle atrophy and strength loss; the recovery of dynamic strength can occur rapidly (within 6 weeks) during retraining.
  • Compared to endurance training, the detraining rate (strength loss) is slower.

Concurrent Strength and Endurance Training

  • Interference Potential: Performing endurance training concurrently may impair strength adaptations primarily due to fatigue from high exercise volumes.
    • It is recommended that the more critical exercise modality be performed first in a workout session.

Notes on Periodization of Training

  • Periodization: Refers to planned variations in training intensity and volume, considered superior by many strength coaches to traditional progressive overload methods.
    • Based on Hans Selye’s General Adaptation Syndrome theory.

Conclusion and Summary

  • Key topics covered include: physiological effects of strength training, neural adaptations, muscle protein synthesis, satellite cells' role in muscle growth, and the consequences of concurrent training.