Identify the most appropriate nutritional strategy in the lead up to a prolonged bout of PA and discuss mechs through which your recommendations may facilitate performance Flashcards
What are the main roles of nutrition before exercise?
maximise CHO availability
ensure adequate hydration
Describe a carb loading regimen 1 week out, with reference to changes in carb intake (% of total energy) and exercise duration.
1 week out: 90 mins PA and 50% CHO diet.
incrementally reduce PA and increase CHO % over the week until you’re at no PA and typical %CHO (~70%) on the day before comp
What is the carb loading regimen previously described called and what are its aims?
Super-compensation.
Aims to deplete THEN replete glycogen stores.
What are the 3 time points we can observe when considering “Pre-exercise” CHO?
- Several days (habitual)
- 3-4 hours prior
- < 1 hour prior
In exercise performance and capacity tests, which diet (3-7 days prior to test) results in improved performance and greater TTE? Mixed diet or high CHO diet?
- references
High CHO > Mixed diet
P<0.01
- Bergstrom et al (1967) and Karlsson et al (1971)
Both studies were prolonged activity (>2 hours for high CHO group)
Benefits of ingesting CHO 3-4 hours before comp?
- increased muscle and liver glycogen
- provides feelings of satiety and comfort
Benefits of ingesting CHO within and hour of competing?
- final boost to muscle/liver glycogen concentration
- provides exogenous source of CHO during exercise as it empties from the stomach
How may glucose ingestion too close to activity hinder performance?
glucose ingestion \+ plasma glucose \+ plasma insulin - plasma glucose and + CHO metabolism (+glycogen utilisation) - Performance?
> also, metabolic disturbances
What did Costill et al (1977) find may happen when ingesting CHO < 1 hour before activity?
Rebound hypoglycaemia.
Is the majority of the evidence in agreement with Costill’s findings on hypoglycaemia?
What sports/events may have to be more cautious?
- no
- events requiring skill or cognitive ability as rebound hypoglycaemia can impact thought clarity and speed.
What is glycaemic index?
the magnitude of the increase in blood glucose following feeding (compared to that of glucose)
What would ingestion of low GI CHO result in compared with high GI?
slower release of glucose, therefore, avoiding a surge of insulin.
Therefore, better maintenance of blood glucose and use of exogenous CHO during PA
How does the amount of CHO ingested before (1 hour) prolonged exercise affect…
a) Insulin conc.
b) extent of rebound hypoglycaemia
c) performance
-reference
- Jentjens et al (2003)
a) higher with greater glucose ingestion (200 g and 75 g vs 20g and placebo)
b) higher insulin conc. doesn’t result in greater blood glucose conc drop.
c) no impact on performance
The fall in blood glucose conc during sub-max exercise, following ingestion of a mod CHO (75 g) within the hour before exercise, cannot be prevented either by ingesting a smaller (22 g) or a larger (>155 g) amount of CHO.
How do the effects of ingesting low GI CHO vs. high GI differ between 1 hour before and 3-4 hours before?
Greater effect seen on TTE when close to PA rather than far away.
Does ingestion of low GI CHO have an impact on metabolic processes and/or performance?
-reference for performance effects
potentially yes to metabolic effects.
not overwhelming evidence for performance benefits, but do have example of Wu & Williams (2006). Low GI meal 3 hours before 70% vo2 max run TTE resulted in greater TTE and fat metabolism than high GI meal.
Outline the +ves of…
a) low CHO (e.g. fasted) training -reference
b) high CHO training
a) a greater level of training adaptations (i.e. mitochondrial biogenesis) - (Hawley & Burke, 2010)
b) better quality of training
Describe how caffeine ingestion (how much?) before prolonged exercise effects performance and metabolic usage.
- give a reference
- Costill et al (1978)
330 mg caffeine or placebo taken 1 hour before cycle TTE @80% vo2 max.
Caffeine = sig greater TTE and sig lower RER throughout (greater fat oxidation compared w/ CHO).
What are the mechanisms through which caffeine has an effect on the body?
> stimulatory effect on the CNS via its antagonistic effect on adenosine receptors (this reduces RPE and/or increases motor unit recruitment)
increases mobilisation of intracellular calcium, facilitating formation of actin-myosin complex.
influences substrate metabolism (inhibits glycogen phosphorylase, therefore, more fat oxidation), as a result of stimulation of adrenaline secretion. Glycogen sparing?
What is a limitation into the findings of ‘train low’?
-reference
- Burke et al (2011)
> reduced training intensity
> no convincing evidence that train low strategies enhance performance over conventional methods.
What is the theory as to why pre-exercise ingestion of solid CHO would be better for performance than liquid?
- reference
ingestion of solid food significantly slows GE rates, whereas liquid facilitates GE.
Slower GE = slower release of CHO in to blood. Therefore, solid food would provide a slower, more sustained release of glucose into the blood.
- Jeukendrup (2010)
How does ingestion of solid vs. liquid CHO pre-exercise affect blood glucose conc, CHO oxidation and performance?
- reference
no difference in blood glucose conc, CHO oxidation rates (Pfeiffer et al (2010) or performance (Neufer et al, 1987)
What did the Jeukendrup (2010) review conclude with regards to ingesting CHO before prolonged exercise?
based on current available evidence there doesn’t appear to be reason to avoid CHO before exercise as there are no detrimental effects to performance.
Those prone to rebound hypoglycaemia or symptoms can navigate this by choosing a low GI CHO or consuming CHO just before exercise.
How does CHO ingestion timing within (within the hour before) affect metabolic response?
-reference
- Moseley et al (2003)
75 g glucose either 15,45 or 75 mins before prolonged exercise. Plasma glucose and insulin conc higher immediately pre-ex with 15 min group, differences in plasma glucose disappeared after 10 mins of exercise.
What is the general consensus on whether ingestion of CHO during the hour before prolonged exercise benefits performance?
Research finds either no performance effect or a benefit (Sherman et al, 1991), despite elevated insulin levels and initial drop in blood glucose.
