Responses and Adaptations to Resistance Training

Chapter 5: Responses and Adaptations to Resistance Training

Objectives

  • Describe the acute responses and chronic adaptations to resistance exercise.
  • Identify factors that affect the magnitude or rate of adaptations to resistance training.
  • Identify how to design resistance training programs that maximize specific adaptations of interest.
  • Identify how to avoid overtraining with resistance training programs.
  • Describe the effects of detraining and identify how to reduce them.

General Adaptations to Resistance Training

Key Concepts
  • Resistance Training Sessions: Resistance training results in a stress response that, if managed properly, can lead to positive adaptations.
  • Progressive Overload: This is essential for ensuring adequate stress and optimization of training adaptations.
  • Chronic Training Adaptations: These adaptations occur in phases, generally moving from strength to mass and tone, then to bone density.
  • Individual Variability: Responses to resistance training vary significantly based on factors such as sex, age, genetics, and environmental influences.

Acute Responses and Chronic Adaptations

Acute Responses
  • These are changes that occur during and shortly after training sessions.
Chronic Adaptations
  • These adaptations take place after repeated training sessions and persist over time.
  • The accumulation of acute responses facilitates the onset of chronic adaptations.
  • Optimal adaptations necessitate a progressive overload scheme in the design of training programs.

Acute Responses to Training

Neurological Changes
  • Changes in the recruitment and firing rate of motor units during a set occur as a result of fatigue.
Muscular Changes
  • Metabolite Accumulation: Includes accumulation of substances such as lactate, H+, Pi, and ammonia.
  • Depletion of Fuel Substrates: Includes:
      - Decrease in creatine phosphate levels.
      - Reduction in glycogen levels.
Endocrine Changes
  • Initial Training Phase (3-4 weeks): Shows a balance between muscle protein synthesis and breakdown.
  • Later Training Phases: Exhibit an increase in net protein balance and elevation in muscle protein synthesis rates.
  • The hormonal response depends on training session characteristics, showing greater responses with:
      - Higher volume and shorter rest intervals.
      - Exercises involving large muscle masses.

Chronic Adaptations

Table 5.2: Chronic Adaptations to Resistance Training
MUSCLE PERFORMANCE
  • Muscular Strength: Increase
  • Muscular Endurance: Increase
  • Power: Increase
MUSCLE ENZYMES
  • Phosphagen System Enzyme Concentrations: May increase
  • Phosphagen System Enzyme Absolute Levels: Increase
  • Glycolytic Enzyme Concentrations: May increase
  • ATP Concentration: Increase
  • Creatine Phosphate (CP) Concentration: Likely increase
MUSCLE SUBSTRATES
  • Lactate Increase During Exercise: Increase
  • ATP and CP Changes During Exercise: Decrease
MUSCLE FIBER CHARACTERISTICS
  • Type I Cross-Sectional Area (CSA): Increase
  • Type II CSA: Increase
  • Percentage of Fiber Types:
      - % Type IIa: Increase
      - % Type IIx: Decrease
      - % Type I: No change
BODY COMPOSITION
  • Fat Mass: Likely decrease
  • Lean Mass: Increase
NEUROLOGICAL CHANGES
  • EMG Amplitude During Maximal Voluntary Contraction (MVC): Likely increase
  • Motor Unit Recruitment: Likely increase
  • Motor Unit Firing Rate: Increase
  • Cocontraction: Decrease
STRUCTURAL CHANGES
  • Connective Tissue Strength: Likely increase
  • Bone Mass and Density: Likely increase
Neurological Changes
  • Linked significantly to strength gains observed within the first 1-2 months of training.
  • Improvements include:
      - Better form and technique
      - Enhanced motor unit recruitment and firing rates
      - Increased synchronization of motor units
      - Decreased cocontraction
Muscle Tissue Changes
  • Hypertrophy: Increased cross-sectional area of muscles; more significant in type II fibers compared to type I.
  • Increase in the number of myofibrils (comprising actin and myosin) along with cytoskeletal and structural proteins.
  • Hyperplasia: No evidence supporting an increase in the number of muscle fibers in humans.
  • Fiber subtype transition from type IIx to type IIa due to resistance training.
  • Potential long-term shifts from type I to type II or vice versa depending on training duration and type.
Skeletal Changes
  • Bone Mineral Density: Influenced by the magnitude and rate of strain during training, potentially leading to reduced risk for osteoporosis.
  • Tendon and Ligament Changes: Tendons adapt to the loads imposed by training, possibly increasing cross-sectional area and altering mechanical properties. Limited data exists on ligament adaptations.
Cartilage Changes
  • Training shown as effective for osteoarthritis treatment, but effects on cartilage remain inconclusive.
Metabolic Changes
  • An observed decrease in mitochondrial density without changes in total mitochondrial numbers.
  • Variational impacts on absolute levels of anaerobic metabolic enzymes and substrates.
  • Endurance Capacity: Increased due to enhanced levels of creatine kinase and glycolytic enzymes.
Endocrine Changes
  • Notable minimal evidence regarding changes in resting hormone concentrations.
  • Enhanced sensitivity of tissues to hormones with acute responses following resistance training.
Cardiorespiratory Changes
  • Adaptations in aerobic fitness most likely influenced by age and pre-existing fitness levels.
  • Resistance training does not negatively impact maximal oxygen consumption development, instead may augment aerobic endurance performance through improved strength and power.
Body Composition Changes
  • Increased fat-free mass and potential decrease in fat mass over time.

Factors Influencing Adaptations

Specificity of Training
  • Adaptations are specific to the exercise stressor, enhancing performance when similar stressors are applied.
  • Adaptations are also specific to the velocity of muscle action during training.
Sex Differences
  • While males and females generally respond similarly to training, differences exist in strength gains, muscle mass, and acute hormone responses.
  • Notably larger strength differences in upper body versus lower body strength; regardless, relative strength remains comparable, with absolute strength greater in males.
Age Considerations
  • Sarcopenia: The loss of muscle mass due to aging after the age of 30, along with declines in force production and rapid force generation.
  • High-intensity resistance training can mitigate or reverse sarcopenia effects and positively affect bone mineral density.
Genetics
  • Genetic factors may influence the capacity to adapt to training stimuli.

Overtraining

Definition of Overtraining
  • Overtraining arises when training is excessive, often characterized by inappropriate levels of volume or intensity.
  • Overtraining is frequently a result of rapid progression that exceeds the body’s adaptation capacity, leading to:
      - Diminished strength and power capabilities
      - Decreased neuromuscular performance
Scenarios of Overtraining
  • Overuse Injury: Resulting from joint or muscle misuse.
  • General Overtraining: Leading to mood fluctuations, lethargy, and strength plateaus.
Symptoms of Overtraining
  • A plateau followed by a decline in strength gains.
  • Disturbances: Includes sleep issues and decreased appetite.
  • Possible significant lean body mass loss (when not dieting).
  • Persistent flu-like symptoms and lack of enthusiasm for training.
  • Increased muscle soreness.

Detraining

Definition of Detraining
  • Detraining refers to physiological and performance adaptations that decline after ceasing an exercise training program.
  • Changes induced by detraining are the opposite of those achieved through training:
      - Loss of muscle mass
      - Decreased strength and power
Short-Term Detraining Effects
  • Short-term detraining (up to 14 days) generally has minimal effects on muscular strength and explosive power for resistance-trained individuals.
Extended Detraining Effects
  • After prolonged periods of detraining (approximately 48 weeks), significant reductions in muscular strength occur.
  • The extent of strength loss correlates with the loads used during training prior to cessation.