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2992 Lecture 6_Muscle Adaptation_Student.pdf
- 1. School of Kinesiology MuscleAdaptation KIN2992: Fitness Assessment and Strength Training
- 2. • Learners willhave the opportunity to • Review muscle function • Learn about muscle metabolism: • Muscle protein synthesis • Muscle protein breakdown • Learn about muscle adaptation: • Stimulus (training) • Response (growth/adaptation) 1 Learning Outcomes Muscle Adaptation
- 3. Muscle Function 2 Muscle Adaptation MusclePerformance • Muscular strength: force a muscle or muscle group can exert in one maximal effort. • Muscular power: The ability of a muscle or muscle group to generate force while shortening. • Muscular endurance: Ability of muscles or muscle groups to perform repeated or sustained contractions.
- 4. Muscle Function 3 Muscle Adaptation MusclePerformance • Muscular strength: force a muscle or muscle group can exert in one maximal effort. • Muscle size, contractile density, neural drive • Muscular power: The ability of a muscle or muscle group to generate force while shortening. • Strength, crossbridge cycling rates • Muscular endurance: Ability of muscles or muscle groups to perform repeated or sustained contractions. • Metabolic supply: capillary and mitochondria density, myoglobin content, oxidative enzymes
- 5. 4 Muscle Adaptation Muscle FibreTypes Type I (slow) Type IIa Type IIx Twitch Duration Long Short Shorter Myofibrillar density Low(er) High High(est) Force output Low Medium High Crossbridge cycling rates Low High High(er) Contraction speed Slow Moderately fast Fast Mitochondria density High High Moderate Capillary density High Moderate Low Myoglobin High Moderate Low Fatigue resistance High Fairly High Moderate Strength Power Endurance
- 6. 5 Muscle Adaptation Muscle FibreTypes Type I (slow) Type IIa Type IIx Twitch Duration Long Short Shorter Myofibrillar density Low(er) High High(est) Force output Low Medium High Crossbridge cycling rates Low High High(er) Contraction speed Slow Moderately fast Fast Mitochondria density High High Moderate Capillary density High Moderate Low Myoglobin High Moderate Low Fatigue resistance High Fairly High Moderate Both Slow and fast fibres can adapt to have characteristics of faster or slower fibres Preferentially hypertrophy slow fibres or fast (or both) based on how they are challenged (specificity/overload)
- 7. School of Kinesiology MuscleMetabolism KIN2992: Fitness Assessment and Strength Training
- 8. Muscle Protein Balance 7 MuscleAdaptation Muscle Metabolism • Muscle is great! • …But it is “expensive” (McNab, 2019) Muscle costs ~6x as much as stored fat to maintain (Nelson et al., 1992)
- 9. Net Muscle ProteinBalance (NBAL) 8 Muscle Adaptation Muscle Metabolism • Muscles constantly undergoing adaptative and reparative processes: • Muscle protein breakdown (MPB): • Muscle protein synthesis (MPS): Amino acids delivered to muscle are used to form muscle proteins that comprise new myofibrils Muscle proteins broken down into constituent amino acids, that are used for energy or to synthesize other body proteins
- 10. Net Muscle ProteinBalance (NBAL) 9 Muscle Adaptation Muscle Metabolism • Muscles constantly undergoing adaptative and reparative processes: • Muscle protein breakdown (MPB): • Muscle protein synthesis (MPS): MPB > MPS = negative NBAL = muscle atrophy MPS > MPB = positive NBAL = muscle growth
- 11. Net Muscle ProteinBalance (NBAL) 10 Muscle Adaptation Muscle Metabolism • Muscles constantly undergoing adaptative and reparative processes: • Muscle protein breakdown (MPB): • Muscle protein synthesis (MPS): Catabolic Factors • Caloric deficit • Stress hormones • Energy expenditure (exercise) Anabolic Factors • Resistance exercise • Food intake • Protein intake
- 12. Net Muscle ProteinBalance (NBAL) 11 Muscle Adaptation Muscle Metabolism • Muscles constantly undergoing adaptative and reparative processes: • Muscle protein breakdown (MPB): • Muscle protein synthesis (MPS): For example: following 8 sets of 8 reps of knee extension at 80% 1-RM (Phillips et al., 1997) Exercise stress leads to breakdown Exercise stimuli leads to subsequent synthesis
- 13. Net Muscle ProteinBalance (NBAL) 12 Muscle Adaptation Muscle Metabolism • Muscles constantly undergoing adaptative and reparative processes: • Muscle protein breakdown (MPB): • Muscle protein synthesis (MPS): (Glover et al., 2008) Unloading leads to decreased MPS (maintained MBP) and muscle atrophy For example, following 14 days in a leg cast
- 14. Net Muscle ProteinBalance (NBAL) 13 Muscle Adaptation Muscle Metabolism • Muscles constantly undergoing adaptative and reparative processes: • Muscle protein breakdown (MPB): • Muscle protein synthesis (MPS): Poor sleep: decreases testosterone and increases cortisol = impaired MPS For example, during 5 nights of sleep restriction (4h/night)
- 15. Net Muscle ProteinBalance (NBAL) 14 Muscle Adaptation Muscle Metabolism • Muscles constantly undergoing adaptative and reparative processes: • Muscle protein breakdown (MPB): • Muscle protein synthesis (MPS): Catabolic Factors • Caloric deficit • Stress hormones • Energy expenditure (exercise) Anabolic Factors • Resistance exercise • Food intake • Protein intake MPB > MPS = negative NBAL = muscle atrophy MPS > MPB = positive NBAL = muscle growth
- 16. School of Kinesiology MuscleGrowth KIN2992: Fitness Assessment and Strength Training
- 17. Muscle Growth 16 Muscle Adaptation MuscleAdaptation • Tissues can grow through hypertrophy and/or hyperplasia • Hypertrophy: increase in the size of individual muscle fibres • Hyperplasia: increase in the number of muscle fibres • Only in rare cases, muscles grow through hyperplasia • Predominance (>95%) of muscle growth attributable to hypertrophy Accomplished with an increased number of myofibrils per fibre
- 18. Muscle Growth 17 Muscle Adaptation MuscleAdaptation • Muscle primarily grows through hypertrophy (increase in the size of individual muscle fibres) Strength: accomplished with an increased number of myofibrils per fibre Endurance: accomplished with an increased number of mitochondria and capillaries per fibre Myofibrils Capillaries Mitochondria
- 19. Muscle Growth 18 Muscle Adaptation MuscleAdaptation • Muscle primarily grows through hypertrophy (increase in the size of individual muscle fibres) Strength: accomplished with an increased number of myofibrils per fibre Endurance: accomplished with an increased number of mitochondria and capillaries per fibre Accomplished with an increased number of cellular components per fibre Amino acids delivered to muscle are used to form muscle proteins that comprise new myofibrils
- 20. Muscle Growth 19 Muscle Adaptation MuscleAdaptation • Myonuclear Domain Theory: Each nucleus of a muscle cell is responsible for a finite volume of cell space • In order for a muscle fibre to grow (hypertrophy), the number of nuclei needs to increase. Analogy Time!
- 21. Muscle Growth 20 Muscle Adaptation MuscleAdaptation • Myonuclear Domain Theory: Each nucleus of a muscle cell is responsible for a finite volume of cell space • In order for a muscle fibre to grow (hypertrophy), the number of nuclei needs to increase. • Satellite Cells: quiescent cells that activate and enter the fibre: • Aid in tissue repair and/or • Donate their nuclei
- 22. Muscle Growth 21 Muscle Adaptation MuscleAdaptation Muscle protein synthesis generates new myofibrils or metabolic components within existing fibres (muscle hypertrophy) Satellite cells proliferate and differentiate to form new nuclei to support cell processes of now bigger fibres Exercise Stimulus Adaptation
- 23. Muscle Adaptation Muscle GrowthStimulus 22 Muscle Adaptation • Muscle responds (in specific ways) in response to overload • During resistance exercise: • Muscle ion balance is disrupted (Ca+ influx) • Substrates (PCr and glycogen) are depleted • Metabolites (lactate, H+, ADP, Pi) accumulate • Force is generated • Inflammation cascades are triggered
- 24. Muscle Adaptation Muscle GrowthStimulus 23 Muscle Adaptation • Muscle responds (in specific ways) in response to overload • During resistance exercise: • Muscle ion balance is disrupted (Ca+ influx) • Substrates (PCr and glycogen) are depleted • Metabolites (lactate, H+, ADP, Pi) accumulate • Force is generated • Inflammation cascades are triggered Metabolic Accumulation Mechanical Forces Immune Signaling
- 25. Muscle Adaptation Muscle GrowthStimulus 24 Muscle Adaptation • Muscle responds (in specific ways) in response to overload Metabolic Accumulation Mechanical Forces Immune Signaling Ca2+ H+ Pi Inflammation IL, Testosterone, TGF Mechanical Forces AMPK PGC-1α Mitochondria Biogenesis Capillary Angiogenesis mTOR p70s6K Akt1 Muscle Protein Synthesis Satellite Cell Activation
- 26. Muscle Adaptation Muscle GrowthStimulus 25 Muscle Adaptation • Muscle responds (in specific ways) in response to overload Metabolic Accumulation Mechanical Forces Immune Signaling Ca2+ H+ Pi Inflammation IL, Testosterone, TGF Mechanical Forces AMPK PGC-1α Mitochondria Biogenesis Capillary Angiogenesis mTOR p70s6K Akt1 Muscle Protein Synthesis Satellite Cell Activation Muscle adaptation depends on stimulus. Stimulus depends on loading
- 27. Muscle Adaptation Muscle GrowthStimulus 26 Muscle Adaptation • Muscle responds (in specific ways) in response to overload • Responds to • Metabolite accumulation • Mechanical forces • Immune signaling (inflammation) Muscle adaptation depends on stimulus. Stimulus depends on loading
- 28. 27 Resistance Training Muscle Adaptation FinalThoughts • Muscle composition and size (CSA) dictates its functional performance • Muscle size (growth or atrophy) is dependent on muscle protein balance (MPS and MPB) • Muscles adapt to exercise stimuli by generation of myofibril muscle proteins, and mitochondria and capillaries, and satellite cell differentiation into nuclei • Muscle adaptation stimulated by accumulation of metabolites, detection of mechanical forces, and inflammation
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