Cellular respiration is the process of converting the biochemical energy contained within nutrients into a more readily available form of energy known as ATP. Sugar, or glucose, is a common nutrient broken down in the process; however, you may also obtain energy from fatty acids and amino acids in your diet. Exercise is a high-energy state which requires changes in cellular respiration at the cellular level of skeletal muscle.
Glycolysis
Cellular respiration begins with a series of reactions, known collectively as glycolysis, which breaks glucose down into two molecules of pyruvate. During exercise, glucose transport into cells is increased in order to keep up with accelerating rates of glycolysis. Hormones released during exercise, including insulin and adrenaline, will increase the number of open glucose transporters in the cell membrane. Combined with increased blood flow to muscles, glucose absorption by contracting skeletal muscle will increase in order to provide enough energy to fuel exercise.
Aerobic or Anaerobic
Depending on the availability of oxygen, the pyruvate molecules produced by glycolysis will either enter the mitochondria to complete aerobic respiration, or will be converted into lactic acid through the process of anaerobic respiration. Aerobic respiration is by far more effective at powering the cell than anaerobic, providing 19 times more energy per molecule of glucose. Your body will do everything it can to maintain aerobic respiration during exercise, including changing some of the most basic properties of your muscle cells.
Mitochondrial changes during exercise
According to a 2006 article from York University, with each period of exercise you perform, there are changes in the expression of genes important in the formation and function of mitochondria. Through a process known as mitochondrial biogenesis, exercise has been shown to increase the production of these energy producing cellular structures, thus enabling cells to withstand longer periods of energy expenditure without fatiguing. By increasing mitochondrial volume in skeletal muscle, the cells' ability to perform aerobic respiration is significantly improved with exercise training
Blood Flow
In order to provide enough oxygen to support aerobic respiration, skeletal muscle has been shown to increase blood flow to exercising tissue up to 100 times baseline values. Increasing temperatures, production of lactic acid, and production of carbon dioxide by exercising muscle all contribute to blood vessel dilation and increased oxygen delivery to tissues that need it most. Oxygen is required for aerobic respiration, specifically for the process known as electron transport, which takes place inside the mitochondria. With regular physical training, increased oxygen delivery and biogenesis of mitochondria prepare the muscles for extended periods of exercise.
References
- PubMed.gov: Control of gene expression and mitochondrial biogenesis in the muscular adaptation to endurance exercise; Joseph AM, et.al; 2006
- PubMed.gov: Coordination of metabolic plasticity in skeletal muscle; Hood DA, et.al; June 2006
- PubMed.gov: An overview of muscle glucose uptake during exercise. Sites of regulation; Wasserman DH and Halseth AE; 1998
- PubMed.gov: The physiological regulation of glucose flux into muscle in vivo; Wasserman DH, et.al; Jan 2011
- PubMed.gov: Plasticity of skeletal muscle mitochondria in response to contractile activity; Jan 2003
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