Chapter 5: responses and adaptations to resistance training
Key concepts of this chapter
1. Resistance training sessions result in a stress response; summation of these stress responses
leads to positive adaptations if a program is designed properly
2. Progressive overload ensures adequate stress
3. Chronic training adaptations occur in phases: strength -> mass/tone -> bone density
4. Individuals responds differently to training; sex, age, genetics or environment.
Acute & Chronic Physiological Adaptations
• Acute responses: These are immediate changes that occur in the body during and shortly after an
exercise session. An example is the depletion of fuel substrates like creatine phosphate in muscles.
• Chronic adaptations: These are enduring changes that take place in the body after repeated training
sessions and persist long after the workout is finished. For instance, an increase in muscle mass.
• The accumulation of acute responses from each training session contributes to lasting adaptations
across major organ systems like musculoskeletal, cardiovascular, nervous, endocrine, and immune
systems.
• The key to enhancing muscle size and strength is to subject the neuromuscular system to overload,
meaning it should experience a training stress it's not accustomed to. Progressive overload enables
the muscle to handle heavier loads, indicating various physiological adaptations.
Adaptations during Resistance Training:
• Adaptations to resistance overload: The swift increase in the capacity for muscles to handle heavier
loads at the beginning of a training program suggests heightened activation of motor units in initial
resistance training phases.
• Hypertrophy: Resistance training leads to muscle growth, primarily influenced by genetic factors.
• Early resistance training stages: Research indicates that strength improvements in these stages stem
from neurological adaptations. Muscle protein quality also changes to allow for quicker and more
forceful contractions.
• Cellular adaptations: These involve changes in anaerobic enzyme levels, energy substrate stores,
myofibrillar protein content, and noncontractile muscle proteins.
Acute Training Responses; Neurological Alterations:
• Electromyography (EMG): This method records electrical events, like action potentials manifested as
voltage changes on the sarcolemma, measured via electrodes. EMG amplitude increases.
• Motor unit recruitment: Muscle force control relies on motor unit recruitment and rate coding. More
force-requiring tasks engage more motor units. Higher firing rates result in greater force. Over time,
motor unit recruitment rises compensating for fatigue-related force loss.
• Fast-twitch and slow-twitch motor units: Fast-twitch units require high threshold and serve high-
force actions, while slow-twitch units have a low threshold and are suited for low-force activities.
• Motor unit recruitment follows the size principle, where low-threshold units are activated at low
force levels, and both low- and high-threshold units are engaged at higher force levels.
, Muscular Alterations:
• Accumulated metabolites include lactate, hydrogen ions, inorganic phosphate (Pi), and ammonia.
• Depletion of creatine phosphate during resistance training leads to reduced power.
• Complete glycogen depletion is unlikely but levels decrease after intense resistance training,
emphasizing the importance of carbohydrate-rich diet.
Endocrine Changes: Many hormones influence tissue growth and degradation, including muscle
tissue.
• Anabolic hormones (testosterone, growth hormone, insulin) stimulate muscle growth, while
catabolic hormones (cortisol) aid in maintaining homeostasis.
• Initial training phases (3-4 weeks) show similar synthesis and breakdown rates of muscle protein.
Later phases exhibit increased net protein balance (elevated muscle protein synthesis).
• Exercise raises epinephrine, enhancing fat and carbohydrate breakdown for increased ATP
production. It also affects the central nervous system (motor unit activation).
• Testosterone and GH levels rise during exercise, stimulating protein synthesis.
Chronic adaptations
