resistance training

Resistance Training

Principles of Training

• Overload

  • 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 system involved (aerobic vs. anaerobic)
  • Velocity of contraction
  • Type of contraction (eccentric, concentric, isometric)

• Reversibility

  • Gains are lost when overload is removed.

Physiological Effects of Strength Training

• Muscular strength

  • Definition: The maximal force a muscle or muscle group can generate.
  • Measured as 1 repetition maximum (1-RM).

• Muscular endurance

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

• Strength training types:

  • High-resistance training (2–10 RM):
  • Gains in strength.
  • Low-resistance training (20+ RM):
  • Gains in endurance.

Muscle Adaptations to Anaerobic Exercise Training

• Anaerobic exercise

  • Definition: Short-duration (i.e., 10-30 seconds) all-out effort.
  • Muscle fibers involved: Both type I and II muscle fibers.
  • Energy supply sources:
  • Exercise lasting 10 seconds or less mainly supplied by the ATP-PC system.
  • Exercise lasting 20-30 seconds: 80% of energy provided anaerobically and 20% aerobically.

• Performance increases

  • 4-10 weeks of anaerobic training can increase peak anaerobic power by 3-28% across individuals.

• Muscle buffering capacity improvements

  • Achieved by increasing both intracellular buffers and hydrogen ion transporters.

• Hypertrophy of type II muscle fibers

  • Increases in enzymes involved in both the ATP-PC system and glycolysis.
  • High-intensity interval training (>30 seconds) promotes mitochondrial biogenesis at or above VO2 max.

Resistance Training

• Neural adaptations responsible for early gains in strength occur within the first 8–20 weeks and include:

  • Increased ability to recruit motor units.
  • Altered motor neuron firing rates.
  • Enhanced motor unit synchronization.
  • Removal of neural inhibition.

• Hyperplasia

  • Definition: Increase in muscle fiber number.
  • Limited evidence in humans, with most studies indicating that 90–95% of muscle enlargement is due to hypertrophy.

• Hypertrophy specifics:

  • Both type I and II fibers experience hypertrophy, with a greater degree in type II fibers.
  • Increases in myofibrillar proteins lead to:
  • Increased number of cross-bridges.
  • Increased ability to generate force.

• mTOR (Mechanistic target of rapamycin):

  • A protein kinase that increases ribosome production and accelerates protein synthesis.
  • Leucine and BCAA supplementation provide a small increase in mTOR activation but are ineffective in untrained individuals.

Muscle Fiber Changes

• Fiber type shifts from type IIx to IIa:
  • Change of 5-11% following 20 weeks of resistance training.
  • Small increases in type I fibers occur; however, resistance training-induced fast-to-slow shifts in fiber type are less prominent compared to endurance training.

Concurrent Strength and Endurance Training

• Interference potential:

  • Strength training increases muscle fiber size, while endurance training does not.
  • Degree of interference depends on the intensity, volume, and frequency of the training.

• Impairment of strength gains through concurrent training:

  • Combining strength and endurance training can impair strength gains compared to strength training alone, with the extent of interference depending on workout specifics (intensity, volume, frequency).

• Neural factors affecting strength development:

  • Impaired motor unit recruitment.
  • Limited evidence supports this concept; low muscle glycogen content due to successive bouts of endurance exercise may result in impaired ability to perform subsequent resistance training bouts.

• Overtraining:

  • No direct evidence to prove that overtraining causes impairments in strength gains during concurrent training.
  • Depressed protein synthesis may occur due to endurance training adaptations that interfere (↓mTOR).

Detraining Effects

• Loss of muscle strength and fiber size:

  • A slow decrease in strength of 31% following 30 weeks of detraining, associated with small changes in fiber size:
  • Type I fiber size: -2%
  • Type IIa fiber size: -10%
  • Type IIx fiber size: -14%
  • Changes attributed primarily to nervous system changes.

• Retraining:

  • Rapid regain of strength and muscle size can occur within 6 weeks after resuming training.
  • Strength maintenance is possible with reduced training up to 12 weeks.

Aging, Strength, and Training

• Decline in strength after age 50 due to:

  • Loss of muscle mass (sarcopenia).
  • Loss of both type I and II fibers, including atrophy of type II fibers.
  • Loss of intramuscular fat and connective tissue.
  • Loss of motor units and reorganization of motor units.

• Progressive resistance training:

  • Important for causing muscle hypertrophy and strength gains, which are vital for activities of daily living, maintaining balance, and reducing the risk of falls.

Study Guide Questions

• How does concurrent training impact gains in strength and endurance?
• What is mTOR and why is it crucial in resistance training?
• How do muscle fibers adapt following resistance training?
• What is the difference between hypertrophy and hyperplasia, and which is more relied upon during resistance training?
• What physiological changes occur during the first 8 weeks of resistance training?
• How do strength and muscle size change after periods of detraining, and how do they respond to retraining?
• How is strength affected by aging?