Exercise and Carbohydrates
Types
of CHO
n
Monosaccharides
Basic unit of carbohydrates
Glucose (C6H12O6)
n
Produced in body through digestion
Uses:
n
Energy for the cell
n
Stored as glycogen in muscles and
liver
n
Converted to fats for energy storage
Fructose- sweetest of monosac.;
some absorbed directly into blood
Galactose- forms lactose in mammary glands; can convert to glucose
Disaccharides
n
Monosaccharide + Monosaccharide
n
Examples:
Sucrose glucose + fructose
Lactose glucose + galactose
Maltose glucose + glucose
n
Dietary examples:
Brown sugar, corn syrup, honey
Polysaccharides
n
Plant polysaccharides
Starch complex CHO
Fiber cellulose is most abundent; resists digestive breakdown
n
20-35 grams recommended daily
n
Animal polysaccharides
Glycogen storage form of CHO in the
body
n
Muscle glycogen is major source of
CHO energy for active muscles during exercise
n
Liver glycogen contributes to glucose
needs during exercise
Carbohydrate
Conversions
n
Glycogenolysis breakdown
of glycogen for energy use by muscle and liver
n
Glucogenesis making
glycogen from glucose
n
Gluconeogenesis making
glucose from non-CHO sources, such as protein
Depletion of Muscle/Liver Glycogen
n
Occurs through:
Dietary restriction
Heavy exercise
n
Upon completion of exercise, glucose rebuilding processes
(gluconeogenesis) in muscle and liver will take place
How are glucose levels regulated?
n
Efforts of 2 primary hormones (originating from
pancreas):
Insulin prompts muscle to take up glucose
when blood sugar (glucose) levels get too high
Glucagon prompts
liver to break down glycogen and put glucose into bloodstream
CHO
Role in Body
n
Energy Source
Needed for exercise but excess may be
converted to fat
n
Protein Sparer
If there is enough CHO around,
protein does not have to be used as much as an energy source
n
Metabolic Primer
With decreasing amount of CHO for
energy, fat becomes more important
n
Fuel for CNS
Brain/nervous system use glucose
almost exclusively
Takes brain approx. 8 hrs to use fat
effectively
Systems of low glucose (hypoglycemia)
weakness, hunger, dizziness
Recommended
CHO Intake
n
Regular exercisers
60% of total calories
n
Heavy exercise training
70% of total calories
n
*Interesting notes:
CHO account for 40-50% of current
American diet
Current annual sugar intake approx.
60 lbs of table sugar per person compared to 4 lbs per person 100 years ago
Using
CHO During Exercise
n
As exercise intensity increases,
the amount of glucose use will increase. It is preferred (compared to fat and
protein) at higher intensities because it can be supplied twice as fast
n
Moderate and Prolonged Exercise
Rest to submax
exercise most of CHO energy comes from active muscles
Longer than 20 min CHO from both
muscle and liver
When CHO in muscle and liver run low
from prolonged exercise, fatigue will occur and endurance athletes tend to
experience hitting the wall phenomenon