#39 - Why muscle glycogen is important with Dr Niels Ørtenblad
Mar 25, 2023
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Dr Niels Ørtenblad, an expert on muscle glycogen from the University of Southern Denmark, discusses the history of muscle glycogen research, the effects of diet and exercise on glycogen levels, the correlation between glycogen and muscle fatigue, and the efficiency of carbohydrate use during exercise. The podcast also explores the relationship between exercise intensity and glycogen utilization, the impact of calcium levels on glycogen depletion, and the importance of collaboration in scientific research.
Maintaining optimal levels of muscle glycogen is crucial for sustaining high-intensity exercise and delaying fatigue.
Early researchers established the belief that carbohydrates, including glycogen, were the primary source of energy during exercise, laying the foundation for our understanding of glycogen's importance in exercise physiology.
The complex relationship between muscle glycogen, calcium release, and excitability highlights its crucial role in enabling muscle contraction and maintaining muscle function.
Deep dives
The importance of muscle glycogen for exercise intensity and fatigue
Muscle glycogen plays a crucial role in exercise intensity and fatigue. As exercise intensity increases, the reliance on carbohydrates, specifically glycogen, also increases. Higher intensity exercise requires more glycogen for energy. Additionally, during prolonged exercise, muscle glycogen can become depleted, leading to fatigue. This link between muscle glycogen and fatigue has been extensively studied, exploring factors such as different exercise intensities, durations, carbohydrate ingestion, and endurance training. Overall, maintaining optimal levels of muscle glycogen is essential for sustaining high-intensity exercise and delaying fatigue.
The historical background of glycogen and its importance for exercise
Glycogen was discovered in the mid-1800s, along with the observation that lactate levels were higher in active muscles. Early researchers established the general belief that carbohydrates, including glycogen, were the primary source of energy during exercise. It wasn't until the early 1900s that the use of fatty acids for energy during exercise was established. Further studies in the 20s and 30s demonstrated that glycogen levels affect exercise capacity, showing that high glycogen levels enable longer exercise duration. These pioneering studies laid the foundation for our understanding of glycogen's importance in exercise physiology.
The role of muscle glycogen in calcium release and excitability
Glycogen utilization in muscle affects calcium release and the excitability of muscle fibers. Adequate levels of ATP, produced locally via glycogen metabolism, are necessary for opening calcium release channels and supporting muscle contraction. Glycogen's proximity to the sarcoplasmic reticulum, where calcium is released, suggests that glycogen-derived ATP is crucial for enabling calcium release and subsequent muscle contraction. Additionally, glycogen metabolism fuels the sodium-potassium pump, which helps maintain muscle excitability. These factors highlight the complex relationship between muscle glycogen, calcium release, and excitability.
Importance of Glycogen in Muscle Function
Glycogen is important for muscle function and performance. While some studies suggest that glycogen sparing during exercise may not be significant, it is still essential for overall muscle function and performance. Prolonged exercise and high-intensity intermittent exercise can improve performance by utilizing glycogen. However, the exact localization and distribution of glycogen within muscle fibers is still being explored.
Different Compartments and Localization of Glycogen
Glycogen in muscle fibers is located in three main compartments: below the muscle membrane, around the myofibrils, and inside the myofibrils. Studies indicate that glycogen utilization and distribution vary between different fiber types and within fibers of the same type. The localization of glycogen within the muscle fiber may contribute to markers of fatigue and endurance. Further research is needed to better understand how different pools of glycogen affect muscle function and fatigue.
Dr Glenn McConell chats with Professor Niels Ørtenblad from the University of Southern Denmark. He is an expert on muscle glycogen. We discussed the history of muscle glycogen and exercise research, the effect of diet and exercise training on muscle glycogen levels and use, the distribution and use of muscle glycogen within different muscle fibre compartments, unusual to fully deplete muscle glycogen during exercise and the potential role of muscle glycogen depletion in muscle fatigue. Very interesting stuff. Niel’s Twitter: @nortenblad. 0:00. Introduction and Niels background 6:15. History of the study of muscle glycogen and exercise 9:15. Muscle glycogen and lactate 11:38. Correlation does not imply causation 12:10. Fat use during exercise is less efficient than CHO 14:12. Diet, muscle glycogen and exercise performance 16:00. 1920s and 1930s a golden age of exercise physiology 18:20. Bengt Saltin undertook 30,000 muscle biopsies 20:00. Effect of intensity and duration on muscle glycogen use 21:20. Diet and muscle glycogen use 23:15. High glycogen results in high glycogen use during ex 24:33. Exercise training results in higher muscle glycogen levels 25:51. Why “waste” muscle glycogen when it’s high 27:30. Energy faster from carbohydrate than from fat 28:40. Carbohydrate ingestion and muscle glycogen use 32:05. Glycogen particles / location within the muscle and fatigue 36:51. Calcium release, glycogen levels and fatigue 40:20. Unusual to fully deplete muscle glycogen during exercise 42:40. Muscle glycogen depletion in different muscle fibers 45:30. How muscle glycogen effects muscle calcium release 49:55. How muscle glycogen effects muscle calcium uptake 51:53. Muscle glycogen and excitation-contraction coupling 57:18. Diabetes and muscle glycogen use during exercise 58:17. Muscle glycogen use during exercise in male vs females 59:24. Need really high muscle glycogen?/increases body weight 1:04:16. Studies he’s excited to do 1:05:38. Should try to disprove your hypothesis 1:08:20. Takeaway messages 1:09:30. Glycogen particle size with glycogen use/diet 1:13:40. Outro (9 secs) Inside Exercise brings to you the who's who of research in exercise metabolism, exercise physiology and exercise’s effects on health. With scientific rigor, these researchers discuss popular exercise topics while providing practical strategies for all. The interviewer, Emeritus Professor Glenn McConell, has an international research profile following 30 years of Exercise Metabolism research experience while at The University of Melbourne, Ball State University, Monash University, the University of Copenhagen and Victoria University. He has published over 120 peer reviewed journal articles and recently edited an Exercise Metabolism eBook written by world experts on 17 different topics (https://link.springer.com/book/10.1007/978-3-030-94305-9). Connect with Inside Exercise and Glenn McConell at: Twitter: @Inside_exercise and @GlennMcConell1 Instagram: insideexercise Facebook: Glenn McConell LinkedIn: Glenn McConell https://www.linkedin.com/in/glenn-mcconell-83475460 ResearchGate: Glenn McConell Email: glenn.mcconell@gmail.com
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