Hypertrophy vs Hyperplasia in Muscle Growth

Hypertrophy vs Hyperplasia

• Hypertrophy: existing muscle cells get larger, increasing muscle cross-sectional size
• Hyperplasia: increase in overall muscle fibers
• Difference: hypertrophy involves muscle cell growth, while hyperplasia involves an increase in the number of muscle fibers

Role of Satellite Cells

• Myogenic stem cells that mediate hypertrophy and hyperplasia
• Migrate to damaged cells and donate nucleus to help repair and grow
• Become active due to skeletal muscle stimulus

Components of Hypertrophy

• Increase in myofibrils (actin and myosin filaments)
• Increased sarcoplasm
• More connective tissue

Types of Hypertrophy

• Transient: short-term "muscle pump", muscle swelling due to blood flow to tissue
• Chronic: long-term changes that withstand over time, generally contribute to strength training

General Mechanisms of Hypertrophy

• Exercise causes muscle tension, sarcomere disruption, and metabolic stress (increase in H+ ions)
• Stimulus serves as a trigger for muscle growth due to overcompensation of protein synthesis

Delayed Onset Muscle Soreness (DOMS)

• Caused by eccentric activities
• Occurs 12-48 hours after strenuous exercise

Skeletal Muscle Adaptations to Aerobic Training

• Mitochondrial density: creates more energy (ATP) for the cell
• Mitochondria size: more efficient, with more ETC along the membrane, increasing ATP production
• Increased oxidative enzymes: more enzymes in the Krebs Cycle and ETC used earlier, allowing the body to rely on oxidative pathways and fully metabolize carbs and fats
• Increased MCT transporters: training increases lactate production, requiring more transporters to manage blood lactate levels via the Carnitine Shuttle
• Increased myoglobin: more oxygen carried to the muscle and made available to mitochondria for oxidative metabolism
• Increased capillary density: greater surface area for gas exchange, decreasing diffusion distance
• Increased blood volume: improved delivery of oxygen, lipids, and glucose around the body
• Lower lactate levels: lactate threshold reached at a higher VO2 max due to being better at using oxidative energy systems to metabolize lactate
• Reduced glycogen depletion: glycogen used when we can’t rely on lipids for energy, with more glycogen available for anaerobic energy production