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Basic Exercise Physiology: Gastrointestinal (GI) tract

Icon of calendar18/11/2022

To understand the mechanism behind the effects of our intra-activity drink mix, basic exercise physiology needs some clarification. Gastrointestinal (GI) tract, energy provision, muscle force and fibre types will be discussed upon the following articles. 
We start with Gastrointestinal (GI) tract.

The gastrointestinal (GI) tract is responsible for the metabolism and absorption of nutrients and fluids from food consumption. Starting from the mouth, the food travels via the oesophagus to the stomach and via the intestines to the colon to the anus where all unmetabolized food is secreted as faeces (Greenwood-Van Meerveld et al., 2017). When the food arrives in the stomach, the time it takes to enter the duodenum differs. Factors that can influence gastric emptying rate are volume, energy density, osmolality and exercise. Increased volume in the stomach speeds up the rate of emptying to its maximum emptying capacity. Next to volume, energy density also plays an important role on the gastric emptying rate of the stomach. Consumption of high energy dense foods reduces the gastric emptying rate and similar effects were seen with beverages high in osmolality. Gastric emptying also slows down when exercising.
After gastric emptying the food enters in the duodenum where it is metabolised and absorbed into the bloodstream. Factors that influence gastric emptying rates also influence intestinal absorption, like osmolality and exercise. Other factors are carbohydrate content, other actively transported compounds, and sodium concentration. Fast gastric emptying increases the intestinal absorption. Water absorption depends on the osmolality of drink. Hypotonic beverages are being faster absorbed than hypertonic and isotonic beverages, but isotonic beverages are still being better absorbed than plain water. Carbohydrates are co-transported with sodium to create a gradient to absorb water. Exercise does not directly influence absorption rates; however, a leaky gut can occur during exercise causing nutrient being absorbed directly in the bloodstream causing irritation (Leiper, 2015). After all nutrients are being metabolised and absorbed, the unabsorbed compounds travel to the colon where the last fluids are being absorbed before it is secreted as faeces (Greenwood-Van Meerveld et al., 2017).
Next up is the energy provision in the human body.