Module 2: CHO Recommendations for Athletes Flashcards
Consuming CHO wil?
- Maintain high rates of carbohydrate oxidation
- Reduce ratings of perceived exertion
- Increase endurance capacity
- Delay the onset of fatigue
- Prevent hypoglycemia
What is the goal for blood glucose levels during sport?
To keep BG levels as stable and as close to the normal range as
possible during exercise (~4-6mmol/L)
* Less variation = constant availability of CHO to fuel activity = stable performance
* Some variation will occur BUT adequate nutrition during training and before, during and after activity can help to limit the magnitude of BG fluctuations
* To prevent hypoglycemia
* To spare glycogen
How are glycogen stores utilized?
The body will do everything it can to keep blood glucose at the 4 grams so
1. muscle glycogen
2. liver glycogen
3. blood glucose
What influences the size of glycogen stores?
diet
Abnormally low levels of glucose in blood <3.3 mmol/L
hypoglycemia
Triggers the release of counter-regulatory hormones to prevent further declines in BG levels and promote gluconeogenesis
hypoglycemia
What hormones does hypoglycemia trigger?
Counter-regulatory hormones
* Epinephrine/norepinephrine
* Glucagon
* Cortisol
Adrenergic manifestations with hypoglycemia
- Shakiness, anxiety, nervousness
- Palpitations, tachycardia
- Pallor, coldness, clamminess
- Dilated pupils (mydriasis), blurred vision
- Feeling of numbness “pins and needles” (paresthesia)
- Fatigue, weakness, incoordination
- Impaired judgement
Glucagon/Cortisol manifestations with hypoglycemia
- Hunger
- Nausea, vomiting, abdominal discomfort
- Headache
Stimulus and action of glucagon
- Stimulus: Decrease in blood glucose; Exercise stress
- Action: Promotes gluconeogenesis in liver; helps increase blood glucose levels.
Stimulus and action of cortisol
- Stimulus: Exercise stress; decrease in blood glucose
- Action: Promotes breakdown of protein and resultant gluconeogenesis; helps increase blood glucose levels
Stimulus and action of epinephrine
- Stimulus: Exercise stress; decrease in blood glucose
- Action: Promotes glycogen breakdown and glucose release from the liver: helps increase blood glucose levels
How to prevent hypoglycemia in athletes
- Adequate CHO intake on a daily basis - promote euglycemia
- CHO rich, pre-training or pre-event meal or snack before activity - good BG at onset of activity
- CHO feeding during prolonged activity - “top up”
- CHO rich re-feeding after activity - repletion of glycogen stores
Reactive hypoglycemia
A condition in which low BG levels are induced by a combination of:
1. The timing of an athlete’s intake of CHO-rich foods/beverages
2. The time of the start of activity.
How does reactive hypoglycemia happen?
Excessive glucose intake by an athlete whose BG levels are marginally acceptable in the hour before activity can trigger an excessive release of insulin before exercise promotes skeletal muscle glucose uptake.
* Exercise (muscle contractions) also stimulate glucose uptake.
* results in hypoglycemia
preventing reactive hypoglycemia before activity
CHO rich, pre-training or pre-event meal or snack before activity
* Ensures the athlete’s BG levels are within the normal range at the onset of activity
preventing reactive hypoglycemia during activity
CHO feeding during prolonged activity
* “Tops up,” blood glucose levels quickly and spares glycogen
preventing reactive hypoglycemia after activity
CHO rich re-feeding after activity
* Promotes repletion of glycogen stores used to fuel activity
Difference between regular CHO intake and immediate sport performance
- To support immediate sport performance, (pre/during/post exercise) the focus should be on quickly oxidized CHO
- Throughout the rest of the day, athletes should focus on nutrient- rich sources of CHO, regardless of oxidation rate, including fruits, vegetables, whole grains and legumes
recommended fiber intake from food
25-30 g/d
Why are CHO recommendations higher for athletes?
Meant to support CHO availability for the muscle and central nervous system based on the demands of the sport.
How are recommendations for CHO given to athletes?
based on bodyweight
* And sport, intensity and duration
Daily CHO intake for strength training
4-7 g/kg/day
* CHO may increase the total amount of work an athlete is able to complete during longer duration, high volume training sessions
* Athletes should consume an amount of CHO that they can tolerate and makes them feel energized during their workout
Daily CHO intake for endurance athletes
6-10 g/kg/day - moderate training
8-12 g/g/day - heavy training
* Fatigue in an endurance athlete is often due to depleted muscle glycogen and low levels of blood glucose