Utilization of carbohydrates as fuels during exercise depends primarily on the intensity and duration of the activity. Generally, carbohydrate use increases with increasing intensity and falls with increasing duration of an exercise activity. Glucose is an important carbohydrate in human biology. Cells uses it as fuel-source of energy. The breakdown of food molecules in glucose and other simple sugars is what fuels the reactions which take place inside of our bodies.

Glucose breaks down during glycolysis; production of ATP (adenosine triphosphate) through the degradation of glucose in the absence of oxygen. The process of glycolysis yields a small amount of ATP. During glycolysis the three carbon compound pyruvate is produced. When oxygen is present more ATP is produced from further metabolism of pyruvate. During intense exercise, physical activity or when supply of oxygen in muscle is limited pyruvate produced from glycolysis accumulates in the muscle and is converted into lactate.

On glycolysis one glucose can yield 2 ATP and can re-supply depleted ATP in muscle activity. Most of the energy provided for exercise or physical activity, after it started, for about 30 seconds to 2 minutes derives from glycolysis. Fat utilization does not occur fast enough for ATP demands to be met. If the energy source for exercise or physical activity was only fat we wouldn’t be in a position to carry out activities more intense than a fast walk.

While the anaerobic pathway - glucose provide a major energy fuel for short term, high intensity exercise there are some major disadvantages: Only 5% of the available energy from glucose is released during glycolysis thus ATP production can not be sustained for long. Accumulation of lactate increases acidity of muscle cells that in turn inhibits the activity of key enzymes in glycolysis and production of ATP soon slows and muscle fatigue sets in.

glycolysis, exercise and glycolysis

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