Exercise nutrition Flashcards
What are the four sources of energy?
First two are vast but produce ATP slowly
1. Oxidation of fat
2. Oxidation of carbohydrate
Anaerobic glycolysis and phosphocreatinine are smaller stores but produce ATP more quickly
3. Anaerobic glycolysis
4. Phosphocreatinine
What does phosphocreatine fuel?
Any intense movement performed over a few seconds
What is phosphocreatine metabolism like?
Phosphate is liberated from PCr and used to make ATP in the following reaction:
PCr + ADP -> Cr + ATP, ATP is energy required for movement
What is glycolysis?
Conversion of a 6C molecule into 2x £c fragments of pyruvic acid and 2 ATP- very fast
Where does glucose in glycolysis come from?
Glycogen stored in muscle
What else does glycolysis produce?
Lactic acid as a by-product which makes the muscle acidic (6.5 pH) after about 20s of maximal exercise, this in turn inhibits the enzymes of the pathway
How long does the action of phosphocreatinine and glycolysis last?
Both the anaerobic processes only provide enough energy to keep muscles working maximally for about 3-40 seconds
How is energy mainly stored?
Much more stored as fat than carbohydrate
How are carbohydrates stored?
As liver glycogen, muscle glycogen and glucose in bodily fluids
How are fats stored?
Subcutaneously and intramuscularly
What are fats metabolised into?
Glycerol and fatty acids. Fatty acids undergo beta oxidation and glycerol can be used to form glucose/glycogen in glycolysis
What are carbohydrates metabolised into?
From glycogen/glucose into pyruvate via glycolysis, a by-product of which is lactic acid. Pyruvate also forms acetyl-coA and enters TCA cycle to produce ATP, CO2, NADH and FADH2. NADH and FADH2 then enter the electron transport chain which produces ATP and H2O with the addition of oxygen
During light exercise what is the majority of energy from?
Burning of fat
What happens as energy intensity increases?
Use of CHO as an energy source increases.
When does CHO become the dominant fuel source?
At 60% VO2 max
What is hitting the wall?
Limit of fat oxidation- carbohydrate reserves have run out, maximal fat oxidation is only 0.7g/min which is much slower
What percentage of dietary calories should be from CHO in a normal diet and athletes diet?
50% in normal
70% in adults
Recommended amount is 6-10g CHO/kg body weight
How much carbohydrate should be consumed during exercise?
Carb drinks shown to be effective but there is maximum ingested carbohydrate oxidation rate of about 1g/min which is reached at ingestion rate of 2g/min. If higher, GI issues can occur with excess CHO in intestine due to limited number of CHO transporters
How is the rate of protein synthesis measured?
Patient drinks a radiolabelled drink with 13C labelled phenylalanine so that there is a known circulating amount of this circulating amino acid. Muscle biopsies can be taken to determine how much of the labelled amino acids have been incorporated into the muscle fibre. The more that has been incorporated, the more synthesis that has taken place.
When do muscle protein levels increase?
When there is net muscle protein synthesis
What influences synthesis and breakdown of muscle?
It changes diurnally and is highly influenced by feeding. After a meal, there are more amino acids in the pool and therefore higher synthesis
What are the guidelines for an appreciable increase in muscle mass?
8-12 reps at 70-80% of 1-RM, 3 days per week
How can the anabolic response be maximised?
Ingest more protein so that more amino acids are in the muscle pool.
What is the maximal effective dose of protein for stimulating post-exercise MPS rates?
20g- increasing above this to 40g didn’t show any further increase in muscle fractional synthetic rate, just an energy source for liver
How does muscle mass change with age?
20-30 year male- 50% of body weight is muscle mass
75-80 year male- 25% of body weight is muscle mass
How does muscle synthetic response change with age?
Elderly have anabolic resistance to dietary protein- their muscle synthetic response is attenuated.
Give summary of the lecture?
Resistance exercise and protein feeding increase muscle protein synthesis
Maximal effective dose of protein for stimulating post-exercise muscle protein synthesis rates is 20g
Elderly individuals have anabolic resistance to both exercise and protein intake compared to the young
Protein supplements don’t further increase muscle mass after resistance training in adults unlike young adults
