Exercise-Induced Muscle Damage (EIMD)

• EIMD stands for Exercise-Induced Muscle Damage, and recovery is an important consideration.
• Periodization is a training strategy that recognizes exercise as a form of stress.
• A single bout of exercise results in a relatively small but long-lasting improvement in fitness, along with a shorter-term increase in muscle fatigue.
• Exercise-induced muscle damage (EIMD) occurs when the intensity of an activity is high relative to an individual's capacity.
• Exercise featuring eccentric contractions tends to cause EIMD.
• Understanding EIMD is crucial in training programs, and ignoring it may result in injury, dropout, or stalled progress.

EIMD Stages

• There are four initial stages of EIMD.

Initial Stage

• Mechanical factors, such as high tension, contribute to structural damage from force bearing and force generating.
• Damage occurs to the sarcolemma, which involves mechanical disruption and entry for Phospholipase A2, and Calcium via stretch activated channels
• Damage to the sarcoplasmic reticulum (SR) and myofibrillar structures is part of the initial stage.

Intial Events in EIMD

• High temperature, insufficient ATP production, increased free radical production, and reduced pH are components of metabolic events.

Autogenic Factors

• Calcium-activated proteases cause damage.
• Phospholipase A2 causes damage including:
• Leukotrienes and prostaglandins synthesis from Arachidonic acid.
• Lysophospholipids involvement
• Mitochondrial calcium accumulation, lysosomal protease activity, and free radicals.
• Phagocytic and regenerative processes

Exercise and Stress

• Exercise induces stress which can negatively impact fitness if there is insufficient recovery leading to increased fatigue.

Understanding EIMD

• Understanding EIMD is important so as to avoid increased risk of injury, player dropout, or halted progression.

Anaerobic Exercise

• Anaerobic exercise can cause greater muscle damage due to it causing bigger muscle tears in tissue.

Anatomy of Skeletal Muscle

• Entire muscles contain many bundles, all of which are surrounded by epimysium.
• Bundles (Fasciculi) contain individual muscle cells (fibers), which are surrounded by perimysium.
• Muscle fibers contain myofibrils divided into sarcomeres, and are surrounded by endomysium.
• They fuse with tendons, conduct action potentials, and regulate pH and nutrient transport..
• Satellite cells aid muscle growth/development and its response to injury, immobilization, and training.
• Sarcoplasm serves as cytoplasm of muscle cell
• Transverse tubules (T-tubules) are extensions of the plasmalemma that carry action potentials.
• Sarcoplasmic Reticulum (SR) is responsible for Calcium storage.

Myofibrils

• Myofibrils go from muscle -> fasciculi -> muscle fiber.

Sarcomeres

• There are hundreds to thousands per muscle fiber.
• They are the basis of contractile elements with an end to end full length structure
• They have distinctive stripes.
• A bands are dark stripes
• I bands are light stripes
• The H zone is the middle of the A band
• The M line is the middle of the H zone
• The Z Disk provides the common boundary structure.

Sarcomere Protein Filaments

• These are essential for muscle contraction
• Actin are thin filaments that show up lighter under a microscope and contain only actin filaments.
• They are composed of Actin (myosin-binding site), Tropomyosin (covers active site at rest), Troponin (moves tropomyosin).
• They are anchored to the Z disk, Equally spaced out by titan, and Nebulin acts as an anchoring protein.
• Myosin are thick filaments and show up darker under a microscope
• The A band contains both actin and myosin.
• The H zone contains only myosin filaments.
• They are composed of two intertwined filaments with Globular heads that protrude 360 degrees with the ability to interact with actin filaments for contraction.
• Titan stabilizes the sarcomere and centers myosin, and prevents overstretching, and acts like a spring.
• It extends from Z disk to M band, in addition to binding to titan, increasing muscle force when stretched.

Motor Units

• A motor unit comprises a single α-motor neuron and all the muscle fibers it innervates.
• A greater number of operating motor units results in increased contractile force.
• The neuromuscular junction consists of a synapse between an α-motor neuron and muscle fibers.
• It is the site between the neuron and muscle

Generation of Force

• Type 2 motor units exert more force, and Type 1 motor units exert less force.
• Fewer small fibers generate less force than more large fibers
• Twitch, Summation, and Tetanus are aspects of the frequency of stimulation (rate coding).
• Length-tension relation is optimal when sarcomere length equals optimal overlap and the opposite when there is too little overlap.
• Concentric maximal force development decreases as higher speed and eccentric maximal force development increases at higher speed. This describes the speed-force relation

Resistance Training

• Resistance training causes substantial strength gains via neuromuscular adaptations.
• It is important for overall fitness, health, and athletic training programs
• Gains in muscular fitness such as 25-100% strength gain, better force production, and ability to produce maximal movement occur after 3-6 months of resistance training.
• Similar strength gains occur for both young and old.
• Incredible muscle placticity helps produce those gains

Mechanisms of Strength

• Hypertrophy equates to an increase in muscle size and causes increased muscle strength, while atrophy equates to reduced muscle size and decreased muscle strength
• Sources of strength gains and size and altered neural control.
• Strength gain can occur without neural adaptations via plasticity
• Strength gain can occur without hypertrophy, because strength is the property of the motor system.
• Essential elements for this include motor unit recruitment, stimulation frequency, and other neutral factors.

Motor Units

• Motor units are normally recruited asynchronously.
• Synchronous recruitment improves contraction, force development, and capability to exert steady forces.
• Resistance training causes synchronous recruitment and potentially greater motor unit recruitment.
• Likely that a combination of improved motor unit synchronization and motor unit recruitment leads to strength gains

Motor Unit Rate Coding

• Limited evidence suggests that rate coding increases with resistance training, especially rapid-movement, ballistic type training.

Autogenic Inhibition

• Autogenic Inhibition is useful for the prevention of damage to bones and tendons.
• Inhibitory impulses can decrease by training.
• This allows muscles to generate more force
• This may also result in higher feats of strength

Nueral Factors

• Reduced coactivation contributes to strength gain.
• Morphology of neuromuscular junction

Muscle Hypertrophy

• Hypertrophy is an increase in muscle sixe
• Transient hypertrophy (after exercise bout)
• There is edema formation from plasma fluid.
• Gone within hours
• Chronic Muscle Hypertrophy involves structural change in muscle (Fiber hypertrophy, fiber hyperplasia, or both).

Strength Training Adaptations

• High velocity eccentric training maximizes, which disrupts sarcomere Z-line.
• Concentric training may limit muscle hypertrophy, strength gains.
• Intensities as low as 30% 1RM and as high as 90% contribute to Muscle Hypertrophy
• Causes both highs reps (low load) and low reps (high load)

Fiber Hypertrophy Involves

• More connective tissue, myofibrils, actin, myosin filaments, and sarcoplasm
• Resistance training causes increased protein synthesis
• Muscle content is always changing, and in synthesis there is increased degradation and vice versa, the inverse occurs after exercise.

Hormones and Hypertrophy

• Fiber hypertrophy is facilitated by testosterone and growth hormone
• Elevated post exercise levels not required for anabolism and strength.
• Anabolic steroids -> are synthetic and cause large increases in muscle mass

Fiber Hyperplasia

• Is intense strength increase in fiber splitting
• There is also significant Myogenic stem activity

Human Hypertrophy

• Most Hypertrophy is due to fiber hypertrophy
• Higher intensity causes (type II) fiber hypertrophy
• Fiber hyperplasia may occur only with certain exercise in certain individuals.

Neural Activation

• Short-term and long-term increases contribute to muscle strenght.
• They are substantial and are due to voluntary neural activation.
• They are associated with hypertrophy and increased net increases
• Neural factors typically last for the first 8-10 weeks and after that, hypertrophy major factor after first 10 weeks

Atrophy

• Reduction/cessation of activity -> major changes in muscle structure and function.
• Lack of muscle use causes reduced protein synthesis and initiates process of muscle atrophy
• Strength loss is 3-4% a day and continues to detrain
• Immobilization results in reversible effects within the I and II fibers

Detraining

• Detraining leads to decreases in 1RM
• Loss of strenght can be regained (about 6 weeks)
• Once training the goal goal is met, the training needs to be maintained. (Reduce or maintain)

Fiber Types

• Fiber type conversation is possible under certain conditions with cross-innervation, or chronically low frequency stimulation.
• Common transition is Type IIx to Type IIa through 20- week heavy resistance training resulting in increase in static strength and area of muscle.

Protein Synthesis (Increases protein over time)

• Resistance training increases over time
• Eat 20-25g after resistance training
• Eat 1.6 to 1.7g everyday
• Can increase muscle through mRNA, transcription, and synthesis.
• Is stimulated by insulin and translation
• Is safe with proper safeguards in adolescents and elderly people with restored agility.
• Decreases mTOR

E-Coupling

• Depolarization occurs in plasma membrane and gets transmitted.

Sliding Filament Theory

• Nerve impulses are transmitted to neuromuscular junction, leading to calcium release, which shift troponin and cause a power stroke. ATP binds to myosin, and cycle repeats

Explore exercise-induced muscle damage (EIMD) and its importance in training. EIMD occurs when exercise intensity exceeds an individual's capacity, especially with eccentric contractions. Understanding EIMD is crucial for effective training programs to prevent injury and stalled progress.