Carbohydrate Flashcards
History of carbohydrate and exercise? (Levine et al. 1924)
Low blood glucose at the end of a marathon was associated with fatigue and an inability to concentrate
History of carbohydrate and exercise? (Gordon et al. 1925)
Exhaustion, weakness, shock, and other symptoms of hypoglycemia following prolonged effort may be prevented by adequate and timely ingestion of CHO
History of carbohydrate and exercise? (Christensen & Hansen 1939)
A high-CHO diet for 3-7days enabled subjects to exercise for 210min, whereas a high-fat diet reduced performance to 88min
Name different sources of substrate?
CHO
Fat
Amino acids
How to get energy for muscular effort?
Substates are feed into oxidative metabolism to produce ATP
Define glycolysis?
Generation of ATP from glucose to produce pyruvate
What substrate is the most efficient way to produce ATP from the Krebs cycle?
CHO
Why is carbohydrate the most efficient way to produce ATP from the Krebs cycle?
Requires less oxygen to form the same amount of ATP
Effect of exercise on muscle glycogen concentration and stores? (Areta & Hopkines 2018)
Increase in muscle glycogen stores
Exercise might be linked to muscle glycogen stores
Exercise might enable the process of taking in glucose from muscle glycogen storage to be more developed
Name the three processes carbohydrates undergo in the body?
Ingestion
Absorption
Utilisation
How is glucose absorbed?
Na-glucose linked transported 1 (SGLT1) - intestinal lumen to cell microvilli (rate-limited step)
GLUT2 - cell -> capillaries
What rate is glucose absorbed?
60g/hr
What rate is fructose absorbed?
30g/hr
How is fructose absorbed?
GLUT5 -> intenstinal lumen to cell
GLUT2 -> cell to capillaries
Glucose metabolism in the fasted state?
The liver produces glucose through glycogenolysis
Small uptake of glucose through GLUT2 in the liver
Glucose is transferred into circulation where it is delivered to other tissues
Glucose is transferred from the circulation into the muscle, adipose tissue, and the brain
Define glycogenolysis?
The process of producing glucose from liver glycogen
Which transporter transfers glucose and fructose from the cell into the capillaries?
GLUT2
Which transporter transfers glucose from the intestinal lumen to the cell?
Na-glucose linked transported 1 (SGLT1)
Which transporter transfers fructose from the intestinal lumen to the cell?
GLUT5
Which transporter transfers glucose from the circulation into muscle and adipose tissue?
GLUT4
Which transporter transfers glucose from the circulation into the brain?
GLUT2
Name types of monosaccharides?
Glucose
Fructose
Galactose
Name types of disaccharides?
Sucrose
Maltose
Lactose
What makes up sucrose?
Glucose and fructose
What makes up maltose?
Glucose and glucose
What makes up lactose?
Galactose and lactose
Name types of oligosaccharides?
Maltodextrin
Name types of polysaccharides?
Amylopectin
Amylose
Glucose metabolism in the fed state?
Contribution of CHO from the small intestine
Increases glucose concentration in circulation
Pancreas increases insulin concentration on circulation
Reduced glucose production in the liver
Increased uptake in the liver
Increased uptake in the muscle
Increased uptake in the adipose tissue
What is the process of glucose metabolism in the liver? (Gonzalez & Belts 2019)
Glucose is phosphorylated into glucose-6-phosphate by glucokinase (rate-limiting step)
Glucose can be metabolised into liver glycogen
- glucose-6-phosphate -> glucose-1-phosphate -> UPD-phosphate -> liver glycogen
Glucose can be metabolised into trioses
Fructose metabolism in the liver? (Gonzalez & Belts 2019)
Metabolised into trioses
Fructose -> fructose-1-phosphate -> trioses
In what processes are trioses metabolised in the liver? (Gonzalez & Belts 2019)
Gluconeogenesis = glucose Glycolysis = pyruvate (ATP)
The role of glucose kinase receptor protein (GKRP) in glucose metabolism?
In a normal state has a greater affinity to glucokinase
- inhibit phosphorylation of glucose to glucose-6-phosphate
- reduces glucose uptake in the liver
Fructose binds to GKRP and causes an increase in glucokinase
- increases glucose uptake and downstream glycogen
Glucose uptake in the muscle? (Rose & Richter 2005)
Glucose -> glucose-6-phosphate by hexokinase
Glucose-6-phosphate used for glycolysis or glycogenolysis
Which will increase GLUT4 translocation more, exercise or insulin?
Exercise
Recommended carbohydrate intake for light training load (low-intensity or skill-based activities)?
3-5g/kg/day
Recommended carbohydrate intake for moderate training load (moderate exercise, 1hr/day)?
5-7 g/kg/day
Recommended carbohydrate intake for high training load (endurance program, 1-3hr/day)?
7-10 g/kg/day
Recommended carbohydrate intake for very high training load (extreme commitment, 4-5hr/day)?
10-12 g/kg/day
Do carbohydrate diets improve performance? (Reviewed by Burke et al. 2004)
The majority of articles shows that high CHO consumption results in improved exercise performance
When to consider CHO loading?
The activity places a heavy demand on glycogen stores
The activity >90min of continuous activity
Habitual diet produces less than 7-9g/kg BM/day
There are no medical reasons contradicting a high CHO intake for 3-5days
How many grams of water are there per grams of glycogen?
3g
When not to consider CHO loading?
The exercise is not an endurance activity (<60-80min)
The activity would be adversely affected by weight gain associated with loading
Habitual diet is already >8-9g/kg BM/day
The athlete has unstable diabetes, meaning a high CHO diet would put them at risk
The metabolic/molecular effects of exercising in the fasted state? (Barlett et al. 2015)
Relying on fatty acid
Increase in PPARd
Increase in P38MAPK -> increase PGC-1a -> increased translocation
The metabolic/molecular effects of exercising in the fed state (Barlett et al. 2015)
Increase in glucose
Increase in GLUT4 translocation
Blunting of AMPK and P38MAPK -> reduces activation of PGC-1a
6 methods to train low (glycogen)
Low CHO diet Training after an overnight fast No CHO during recovery Sleep low Long training without CHO intake Training twice a day
What supplementation methods can be used to overcome a reduction in exercise intensity?
Caffeine
Mouth rinse
Hydration
Creatine
What is the goal of pre-exercise feeding?
To replenish liver glycogen and encourage some muscle glycogen synthesis so there is enough blood glucose available late in exercise
What is the effect of pre-exercise feeding on substrate oxidation during exercise?
Increase CHO oxidation during exercise at the expense of fat metabolism
What carbohydrate intake is recommended before exercise? (Burke et al. 2011)
> 60min 1-4g/kg consumed 1-4hr before exercise
If Naharudin et al. 2020 was conducted for a longer duration, what do you think the results could be?
CHO had a better performance than placebo and water
The effect of carbohydrate ingestion before exercise on performance? (Reviewed by Jenkendrup & Killer 2011)
Consuming CHO immediately before exercise has no detrimental effect on performance
Hypoglycemia appears to be very individual
How many grams of carbohydrates are in a 500mL of a 6% drink?
= 500ml x 0.06
= 30g
An athlete consumes a 15% drink during a 3hr race. What volume should they consume, assuming they are exercising at a high intensity?
Require 90g/h = 270g
= 270g / 0.15
= 1800ml
Effect of increasing carbohydrate intake on exogenous carbohydrate oxidation during exercise and what is the idea amount? (Jeukendrup & Jentijens 2000)
When the ingestion rate is 60g/hr it shows an exogenous CHO oxidation of around 0.4-1g/min
When the ingestion rate is further increases there is no further increase in CHO oxidation (rate-limiting)
What limits exogenous carbohydrate oxidation?
Intestinal CHO oxidation appears to be the rate-limiting step
Effects of different carbohydrate mixtures on exogenous carbohydrate oxidation? (Jeukendrup 2010)
Maximising ingestion rate doesn’t have an additional benefit on exogenous CHO oxidation
Combining glucose and fructose increases exogenous CHO oxidation compared to glucose alone
4 ways to assess exogenous carbohydrate oxidation during exercise?
Ingestion of a 13C-labelled CHI
Digestion, absorption, oxidation
Body CHO stores
CO2
What’s the equation to determine carbohydrate oxidation?
4.55 x VCO2 - 3.21 x VO2
What’s the equation to determine fat oxidation?
1.67 x VCO2 - 1.67x VO2
What is hydrogel technology?
New sports drink (maltodextrin and fructose) include the addition of pectin and sodium alginate to encapsulate the CHO
The formation of a hydrogel when in the acidic conditions of the stomach
Potential to increase gastric emptying leading to an increased CHO delivery to the muscle and subsequently improved performance
The effect of hydrogel technology and gastric emptying at rest? (Sutehall et al. 2020)
Increased gastric emptying at rest
What further research is needed for hydrogel technology (Barber et al. 2020)
Further work is needed at higher intensities (>70% VO2max) when gastric emptying is reduced
Further work needed at greater ingestion rate
The effect of hydrogel technology on moderate-intensity exercise? (Reviewed by King et al. 2020)
There was no additional effect on moderate-intensity cycling and running performance with hydrogel technology
The effect of the amount of carbohydrate intake on glycogen resynthesis? (Jentiens & Jeukendrup 2003)
Levelling off of the rate of muscle glycogen synthesis after ingestion rate of 1-1.2g/kg BW/hr of CHO
A diet low in CHO may benefit from the addition of protein
What amount of carbohydrate intake results in a levelling off of glycogen resynthesis? (Burke et al. 2004)
In the general diet, there is a levelling off of muscle glycogen storage (muscle glycogen synthesis) at around 10-12g/kg/ BM of CHO
What effects GLUT4 translocation? (Huang & Czech 2007)
Nutrient pathway - increase in insulin to upregulate GLUT4 translocation to the plasma membrane which increases glucose uptake
Energy demand - increase in AMPK and calcium turnover, which increases GLUT4 translocation
The effect of co-ingestion of carbohydrate on performance and liver glycogen? (Gray et al. 2019)
There was an 18% increase in endurance capacity with the co-ingestion of glucose and fructose
Increases in performance were primarily due to increases in liver glycogen storage
The effect of carbohydrate and protein ingestion on the short-term recovery of muscle glycogen? (Betts & Williams 2010)
When CHO intake is optimal the addition of protein has no additive effect on muscle glycogen synthesis
When CHO intake in sub-optimal the addition of protein has an additive effect on muscle glycogen synthesis
Define the carbohydrate recommendation during a cycling event
DAY 1 = light/medium day over a 4hr flat
DAY 2 = 5hr mountain stage with 3 climbs taking 1hr, 30min and 30min and two descents
DAY 1 - 5-6g/kg BM/day overall - 60g/h during cycling - high CHO evening meal to prepare for day 2 DAY 2 - 10-12g/kg BM/day overall - 90g/h during cycling - pre-exercise meal = 1-4g/kg - recovery = 1-1.2g/kg/h for 2-4hrs - evening meal = 2-3g/kg
Assuming the cyclist is riding for 5hr how much fluid is required over the duration of the ride?
Mass = 70kg
Sweat rate = 1.5l/h
Total sweat = 1.5 x 5 = 7.5L
2% BM loss = 70 x 0.02 = 1.4g (1.4L)
Required fluid intake = 7.5 - 1.4 = 6.1L
What carbohydrate intake is recommended during a high-intensity, long-duration workout?
90g/h
What carbohydrate intake is recommended in the first 2-4hr after exercise?
1-1.2g/kg BW/hr
What is the role of glucokinase?
To convert glucose to glucose-6-phosphate in the liver
What is the role of hexokinase?
To convert glucose to glucose-6-phosphate in the muscle
What is the effect of increasing p38MAPK?
Increase PGC-1a -> increased GLUT4 translocation
What is the rate-limiting step in glucose metabolism in the liver?
Glucose -> glucose-6-phosphate via glucokinase
What can increase the translocation of GLUT4 to the muscular membrane?
Exercise
Insulin
What is the relationship between muscle glycogen concentration and VO2max? (Areta & Hopkines 2018)
Muscle glycogen concentration increases as VO2max increases
What doesn’t limit exogenous carbohydrate oxidation?
Gastric emptying does not limit exogenous CHO oxidation
Muscle glucose uptake does not limit exogenous CHO oxidation
What carbohydrate intake is recommended during a low/medium-intensity, long-duration workout?
60g/h
What ingestion rate of carbohydrates causes a levelling off of muscle glycogen synthesis? (Jentiens & Jeukendrup 2003
1-1.2g/kg BM/hr
A successful male 5 and 10km runner (1.65m 58kg) plans to change their training focus with a view completing the first marathon in 6 months time, describe how training volume and intensity might change?
Increase volume
Decrease intensity
A successful male 5 and 10km runner (1.65m 58kg) plans to change their training focus with a view completing the first marathon in 6 months time, what would be the general recommendation for dietary CHO intake?
7-10g/kg BM/day
A successful male 5 and 10km runner (1.65m 58kg) plans to change their training focus with a view completing the first marathon in 6 months time, describe the recommended CHO intake in the days before the morning of and during the race?
Days before - CHO loading
Morning of race - 1-4kg/BM 1-4hrs before
During race - 60g/hr of CHO with multiple transporters
How do maximal rate of fructose oxidation during exercise compare with that of glucose?
- 25%
- 50%
- 100%
- 150%
50%
PGC-1a is a transcriptional factor primarily implicated in?
Promoting mitochondrial biogenesis
