Exercise Physiology: Antioxidants, Fatigue, and Body Composition

Antioxidants and Exercise

Key antioxidants include Vitamin C, Vitamin E, Carotenoids, Glutathione (GSH), and Coenzyme Q10 (Q10).

Enzymatic Antioxidant Systems

• Superoxide Dismutase (SOD)
• Catalase
• Glutathione Peroxidase

Functions of Antioxidants

• Neutralize free radicals by donating electrons (e-) and hydrogen ions (H+).
• Decrease lipid peroxidation both at rest and after exercise.
• Note: Supplementation may not necessarily decrease overall oxidative stress markers.
• Note: Vitamin E supplementation does not appear to decrease neutrophil count after exercise.

Benefits and Roles of Oxidative Species

• Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS) are important for cellular development, function, and as stimuli (cellular messaging) – involved in signaling, enzyme modulation, and gene activation.
• Neutrophils produce superoxide (O2-) via NADPH Oxidase as a defense mechanism within the innate immune system.

Antioxidants and Exercise Adaptation

Antioxidant supplementation might interfere with the induction of molecular mediators crucial for insulin sensitivity and defense mechanisms stimulated by exercise.

Specifically, Vitamin C and Vitamin E may hinder cellular adaptation processes related to developing resistance and strength.

Epigenetics and Exercise

Epigenetic mechanisms include:

• DNA methylation
• Histone modification
• RNA interference

Methylation involves the grouping of genes. If these groups separate (hypomethylation), the gene is expressed. Exercise induces hypomethylation of PGC-1α, PDK4, and PPAR-γ, which is considered a beneficial stress response.

Increased levels of L3MBTL1 are associated with decreased tumor incidence and better survival outcomes.

Exercise-Induced Fatigue

Central Fatigue

• Characterized by a reduction in the number of motor units activated and their firing frequency.
• Can be altered by factors like excitement, motivation, and diversion.
• Endurance exercise leads to the release of Serotonin, which may contribute to reduced performance and increased fatigue perception.
• Nutritional strategies involving water, amino acids (aa), carbohydrates (CHO), and caffeine (which influences dopamine) can impact central fatigue.

Peripheral Fatigue

• Involves the inability of the Na+/K+ pump to maintain ion gradients and alterations in Ca2+ release and uptake within muscle cells.

Potential Causes of Fatigue

Accumulation of metabolites and byproducts, including:

• ADP (Adenosine diphosphate)
• IMP (Inosine monophosphate)
• Mg2+ (Magnesium ions)
• Lactate
• H+ (Hydrogen ions)
• Certain amino acids
• ROS (Reactive Oxygen Species)
• Heat

Metabolic Factors in Fatigue

• Phosphocreatine (PCr) breakdown and depletion.
• Inhibition or limitation of key enzymes like Phosphofructokinase (PFK) and Pyruvate Dehydrogenase (PDH).
• Limitations within the TCA (Tricarboxylic Acid) cycle.
• Limitations in Free Fatty Acid (FFA) oxidation.
• Limitations in Beta-oxidation.
• "Hitting the wall": Severe glycogen depletion.
• "Acid Bath": Significant accumulation of H+ ions, leading to acidosis.

Muscle Physiology Fundamentals

Oxygen Carriers

Myoglobin contains one heme group, while Hemoglobin contains four heme groups, allowing hemoglobin to transport significantly more O2.

Muscle Fiber Types

Type 1 Muscle Fibers (Slow-Twitch)

Optimized for endurance activities.

• Slow Ca2+ release and uptake.
• Low myosin ATPase activity.
• Low glycolytic capacity.
• High levels of myoglobin (giving them a red appearance).
• Large and numerous mitochondria.
• High oxidative capacity.

Type 2 Muscle Fibers (Fast-Twitch)

Optimized for speed and power.

• High capability for electrochemical transmission of action potentials.
• Rapid Ca2+ release and uptake.
• High myosin ATPase activity.
• High rate of cross-bridge turnover.
• Low levels of myoglobin (giving them a white appearance).
• High glycolytic capacity.
• Low oxidative capacity.

Muscle Tissue Adaptations

• Hypertrophy: Increase in muscle fiber size, involving increased DNA content (via satellite cells) and increased protein synthesis.
• Hyperplasia: Increase in the number of muscle fibers (less common in humans).
• Atrophy: Decrease in muscle fiber size, resulting from an increased rate of protein degradation and potentially decreased DNA content.

Protein Turnover in Muscle

Protein turnover refers to the balance between protein synthesis and protein degradation rates.

Functions of Protein Turnover

• Maintenance of Functional Proteins: Compensating for the loss of functional properties or the physical loss of proteins from the body (e.g., replacing damaged Protein A with new Protein A).
• Modification of Functional Proteins: Adapting to internal (endogenous) or external (exogenous) triggers by changing the type of protein present (e.g., replacing Protein A with Protein B).
• Gain of Functional Proteins: Increasing the total amount of functional proteins or synthesizing proteins intended for excretion (e.g., producing more Protein A).

Kinanthropometry: Body Composition Assessment

Heath-Carter Somatotype

A method to classify physique based on three components: Endomorphy (relative fatness), Mesomorphy (relative musculoskeletal development), and Ectomorphy (relative linearity). Average ratings:

• Men: Approximately 3 (Endo) - 5 (Meso) - 3 (Ecto)
• Women: Approximately 5 (Endo) - 4 (Meso) - 3 (Ecto)

Body Scaling Principles

• If Area increases, it scales with Height squared (Height^2). This relates to transversal area and body surface area relative to height.
• If Volume increases, it scales with Height cubed (Height^3). This relates to body volume and mass relative to height or surface area. Body mass depends on volume.
• Typically, gains in body mass are proportionally greater than gains in VO2max.
• Typically, gains in body mass are proportionally greater than gains in muscle transversal area.

Levels of Body Composition Analysis

• Atomic: Basic elements (e.g., Oxygen, Hydrogen, Carbon).
• Molecular: Molecules (e.g., amino acids, fatty acids, water).
• Cellular: Cell components and products (e.g., enzymes, adipokines).
• Tissue-Organ: Tissues and organs (e.g., bone, adipose tissue).
• Whole Body: Body segments (e.g., head, trunk, appendages).

Typical body fat percentages for elite athletes:

• Male: ~15%
• Female: <25%

Body Composition Models and Methods

Two-Component (2C) Model

Divides the body into Fat Mass (FM) and Fat-Free Mass (FFM) based on body volume and body weight.

• Assumed densities: FFM ≈ 1.1 g/ml, FM ≈ 0.9 g/ml.
• Limitation: Can overestimate body fat in individuals with high bone density or muscle mass.

Four-Component (4C) Model

Uses body volume, osseous mineral content, total body water, and body weight for a more accurate assessment.

Common Measurement Techniques

• DEXA (Dual-energy X-ray Absorptiometry) Scan: Measures bone mineral content, fat tissue mass, fat-free soft tissue mass, estimates body water, and assesses appendicular lean soft tissue.
• CT (Computed Tomography) Scan: Differentiates various tissue types based on X-ray attenuation.
• MRI (Magnetic Resonance Imaging): Uses magnetic fields to create detailed images based on the behavior of water molecules in different tissues.
• Bioelectrical Impedance Analysis (BIA): Estimates body composition based on the different electrical conductivity properties of tissues, measuring extracellular and cellular resistance.