Muscle Adaptations and General Adaptation Syndrome

Neuromuscular Adaptations

• Resistance training (3-6 months) leads to enhanced force production and maximal movement.
• Strength gains range from 25% to 100%.
• Neural control changes.
• Muscle hypertrophy occurs.
• Young males exhibit greater strength gain potential.
• Muscle plasticity is higher.

Selye's General Adaptation Syndrome (GAS)

• Explains responses to training stress.
• Individuals adapt or experience exhaustion depending on training stress levels.
• GAS stages: alarm, resistance, adaptation/exhaustion.

General Adaptation Syndrome (GAS) (Detailed)

• Alarm phase: Initial training, performance decreases due to fatigue.
• Resistance phase: Adaptation; system returns to baseline or surpasses it.
• Supercompensation phase: Increased capacity for performance.
• Overtraining phase: Excessive stressors lead to performance suppression or overtraining syndrome.

Muscle Damage & Adaptations

• Unaccustomed exercise (eccentric muscle actions) cause muscle damage.
• High muscle force damages sarcolemma, releasing cytosolic enzymes and myoglobin.
• Damaged myofibrils and noncontractile structures lead to metabolite accumulation.
• Reduced force capacity.
• Delayed-onset muscle soreness results from inflammation.

Glycogen Supercompensation

• Glycogen levels increase after exercise and recovery.
• Low glycogen levels to normal glycogen increased glycogen levels.
• High carbohydrate intake during recovery boosts glycogen stores.

Adaptations to Resistance Training

• Key changes with resistance training include altered muscle fiber size and type, strength improvements, increased mitochondria, and shifts toward a faster muscle fiber type.
• Neural changes include increases in motor unit recruitment rate and synchronization of firing, as well as activation of the stretch reflex.

Adaptations in Force Gradation

• Force generated in a single muscle fiber depends on the number of cross-bridges.
• Five key factors affecting force production include: motor unit recruitment, motor unit discharge frequency, motor unit type, stretch reflex activation, and contraction speed.
• Neuromuscular adaptations increase force output by changing these factors.

Neural Adaptations

• Anaerobic training affects the neuromuscular chain, starting from higher brain centers and influencing individual muscle fiber levels.
• Greater adaptations occur with high-intensity training and show up early in the program.
• Significant neural adaptations lead to strength improvements.
• Motor cortex activity increases with increasing force levels and new exercises/movements.
• Maximal strength and power increase due to factors such as motor unit recruitment, firing rate, and synchronization.

Neural Adaptations (Neuromuscular Junction)

• Anaerobic training changes the neuromuscular junction (NMJ).
• Increased surface area and irregularly shaped synapses.
• Increased nerve terminal length and area and dispersed acetylcholine receptors.

Neural Adaptations (Proprioceptors)

• Anaerobic training improves stretch reflex response, enhancing force development and muscle spindle/elasticity properties, shortening amortization phase and increasing golgi tendon organ (GTO) threshold and, decreasing inhibitory impulses.

Size Principle Adaptations

• Heavy resistance training recruits more muscle fibers in consecutive order based on size (size principle).
• In advanced lifters, the nervous system might allow for recruiting motor units out of order.
• This allows for greater power and speed production.

Muscular Adaptations

• Anaerobic training leads to hypertophy(growth of muscles).
• Connective tissue strength, and glycogen levels, increase.
• Changes in muscle substrate and glycolytic enzyme activity.
• Possible increased mitochondria and capillary density.
• Shifts in fiber type.

Muscular Adaptations (Detailed)

• Muscle growth (hypertrophy) is primarily due to increased size of existing muscle fibers (not the actual number of fibers)
• An increase in muscle strength/power.
• Hyperplasia is a rare event and is not a prominent factor in muscle adaptation.

Satellite Cells & Hypertrophy

• Satellite cells are myogenic stem cells vital in muscle regeneration.
• Acute damage and stretching trigger satellite cell activation and proliferation..
• Satellite cells migrate to injured regions, repair damaged myofibers, and become new myonuclei.
• This is essential to maintain an adequate myonuclear domain which helps with muscle hypertrophy.

Muscular Adaptations (Structural & Architectural Changes)

• Resistance training increases myofibrillar volume, sarcoplasmic density, and sarcoplasmic reticulum and T-tubule density.
• Sodium-potassium ATPase activity increases.
• Sprint training enhances calcium release.
• Resistance training has an impact on the angle of pennation.

Other Muscular Adaptations

• Reduced mitochondrial density.
• Reduced capillary density.
• Enhanced buffering capacity (acid-base balance).
• Muscle substrate and enzyme activity changes.

Connective Tissue Adaptations (Tendons, Ligaments, and Fascia)

• Mechanical forces (exercise) drive connective tissue adaptation.
• Consistent anaerobic exercise modifies the threshold for connective tissue changes.
• Fibroblasts build connective tissue, primarily collagen.
• Type I collagen is found in bone, tendons, and ligaments.
• Types of collagen fibers have similar arrangements to muscle fibers.

Connective Tissue Adaptations (Detailed)

• Tendon changes include increased collagen fibril diameter, more covalent cross-links, an increase in the collagen fibrils, and increased collagen fibril density.
• High load-bearing regions of tissue, including junctions between tendons/ligaments and bone, and the fascia network of skeletal muscle, are impacted by strength.

Connective Tissue Adaptations (Bone)

• Trabecular bone adapts quickly to stimuli, compared to cortical bone, which takes longer.
• The minimal essential strain (MES) threshold is the minimum force needed for new bone formation.
• MES is about one-tenth the force needed to fracture a bone.
• Muscle strength and hypertrophy increase bone load and can lead to increased bone density.

Bone Remodeling

• Weight-bearing forces cause bending, stimulating new bone formation where bending is greatest.
• Osteoblasts actively build new collagen fibers along the bone's periosteum.
• Osteoblasts migrate to deformed areas.
• Collagen fibers mineralize, enhancing bone diameter.

Why Specific Adaptations Occur

• The type of stress (overload) triggers specific adaptive responses.
• High load resistance training prioritizes mechanical stress responses.
• High volume/short rest prioritizes metabolic stress and damage responses.

Review Questions

• Explanation of GAS.
• Significance of neural adaptations to strength changes.
• Impact of reps and load on resistance training adaptations.
• Seven explained neural adaptations.
• Muscular adaptations to anaerobic training.
• Understanding the underlying reasons for muscle fiber hypertrophy.

Explore the intricacies of neuromuscular adaptations due to resistance training, including strength gains and neural control changes. Understand Selye's General Adaptation Syndrome, its stages, and how individuals adapt to training stress. This quiz delves into muscle damage and the phases of adaptation, including alarm and overtraining.