Exercise Physiology - carbohydrates

Examples of Monosaccharides

are the simplest form of carbohydrates, consisting of single sugar molecules such as glucose, fructose, and galactose. They serve as the building blocks for more complex carbohydrates.

Examples of Dissacharides

are carbohydrates made up of two monosaccharide molecules linked together, such as sucrose, lactose, and maltose. They play various roles in energy provision and storage.

Example of Polysaccharides

are complex carbohydrates composed of long chains of monosaccharide units, such as starch, glycogen, and cellulose. They are important for energy storage and structural components in plants and animals.

Monosaccharides - Glucose (C6H12O6) - what are the three pathways after glucose is absorbed?

1. Used as an energy source for cellular metabolism

2. Forms glycogen for storage in liver and muscles

3. Converts to lipid (triclyglycerol) for later energy use (fat)

Monosaccharides - fructose

• fruit sugar/ levulose: found in fruit and honey

• same formula as glucose but slightly different in C-H-O linkages

• can be converted to glucose for energy use

• primarily metabolized in the liver for glycogen and triaclyglycerol synthesis

Galactose

• combines with glucose in mammary glands of lactating animals to make lactose (polysaccharide)

• body converts to glucose for energy use

Oligosaccharides (disaccharides) - sucrose

• glucose + fructose = sucrose (table sugar)

• found in beet and cane sugar, brown sugar, sorghum, maple syrup, honey

• most common dietary sugar

Oligossacharides - lactose

• glucose + galactose = lactose (milk sugar)

• found only in milk and milk products, not in plants

Oligosaccharides - maltose

• glucose + glucose (malt sugar)

• found in breakfast cereals, beer, and germinating seeds

Polysaccharides - starch

• storage form of carbohydrate in plants

• seeds, corn, grains, pastas, cereal

• amylose and amylopectin

• starches with high levels of amylopectin are digested and absorbed rapidly (apple)

• starches with high levels of amylose content break down at a slower rate (bread)olup

Polysaccharides - fiber

• occurs exclusively in plants

• non starch structural polysaccharides

• resist breakdown by digestive enzymes

Glucogenisis

Glycogen synthesis from glucose (glucose - glycogen)(storing glucose)

Gluconeogenisis

Glucose synthesis largely from structural components of noncarbohydrate nutrients (i.e., protein) (protein - glucose) (ex: Body breaking down muscle for energy)

Glycogenolysis

Glucose formation from glycogen (glycogen - glucose) (using glucose)

Glycogen’s storage capacity

• storage carbohydrates in muscle and liver

• muscle stores about 400g of glycogen (1600kcal)(local supply for energy during exercise)

• liver stores about 90-100g of glycogen (400kcal)(maintain blood sugar)

• intramuscular glycogen is major carbohydrate energy source for muscles during activity

Carbohydates role in the body

• energy fuel during intense exercises - quick source of energy (energy derived from breakdown of blood borne glucose and muscle glycogen)

• protein sparer - helps preserve tissue protein

• metabolic primer/ketosis preventer - “primer” for lipid oxidation (needs carbs to efficiently burn fat)

• central nervous system fuel - primary fuel for the brain and other nerve tissue

Carbohydates dynamics during physical activity

• carbohydrates generate 6% more energy than lipid per liter of O2 uptake

• intense short duration: 1 hour decreases liver glycogen by 55%, 2 hour almost depletes liver and muscle glycogen

• moderate and prolonged exercise: transition from rest to moderate activity uses muscle glycogen, lipid is major energy substrate during low intensity and long duration activity

VO2 max

how efficiently your body can use O2 during exercise

Nutrient Metabolic Dynamics during exercise for 2hr

• plasma glucose levels fall into CHO-depleted conditions

• serum fatty acids FFAs increase as exercise duration increases and glucose decreases

• protein’s contribution to energy expenditure increases

• exercise workload decreases under CHO depleted conditions

Effects of diet on glycogen reserves and performance

A carbohydrate-deficent diet rapidly depletes muscle and liver glycogen and negatively affects performance in short term anaerobic activity and prolonged intense aerobic actives.