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

Question 1

What are the main roles of nutrition before exercise?

Answer 1

maximise CHO availability

ensure adequate hydration

Question 2

Describe a carb loading regimen 1 week out, with reference to changes in carb intake (% of total energy) and exercise duration.

Answer 2

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

Question 3

What is the carb loading regimen previously described called and what are its aims?

Answer 3

Super-compensation.

Aims to deplete THEN replete glycogen stores.

Question 4

What are the 3 time points we can observe when considering “Pre-exercise” CHO?

Answer 4

• Several days (habitual)
• 3-4 hours prior
• < 1 hour prior

Question 5

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

Answer 5

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)

Question 6

Benefits of ingesting CHO 3-4 hours before comp?

Answer 6

• increased muscle and liver glycogen

- provides feelings of satiety and comfort

Question 7

Benefits of ingesting CHO within and hour of competing?

Answer 7

• final boost to muscle/liver glycogen concentration

- provides exogenous source of CHO during exercise as it empties from the stomach

Question 8

How may glucose ingestion too close to activity hinder performance?

Answer 8

glucose ingestion 
\+ plasma glucose 
\+ plasma insulin
- plasma glucose and + CHO metabolism (+glycogen utilisation)
- Performance?

> also, metabolic disturbances

Question 9

What did Costill et al (1977) find may happen when ingesting CHO < 1 hour before activity?

Answer 9

Rebound hypoglycaemia.

Question 10

Is the majority of the evidence in agreement with Costill’s findings on hypoglycaemia?
What sports/events may have to be more cautious?

Answer 10

• no

- events requiring skill or cognitive ability as rebound hypoglycaemia can impact thought clarity and speed.

Question 11

What is glycaemic index?

Answer 11

the magnitude of the increase in blood glucose following feeding (compared to that of glucose)

Question 12

What would ingestion of low GI CHO result in compared with high GI?

Answer 12

slower release of glucose, therefore, avoiding a surge of insulin.
Therefore, better maintenance of blood glucose and use of exogenous CHO during PA

Question 13

How does the amount of CHO ingested before (1 hour) prolonged exercise affect…

a) Insulin conc.
b) extent of rebound hypoglycaemia
c) performance

-reference

Answer 13

• 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.

Question 14

How do the effects of ingesting low GI CHO vs. high GI differ between 1 hour before and 3-4 hours before?

Answer 14

Greater effect seen on TTE when close to PA rather than far away.

Question 15

Does ingestion of low GI CHO have an impact on metabolic processes and/or performance?
-reference for performance effects

Answer 15

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.

Question 16

Outline the +ves of…

a) low CHO (e.g. fasted) training -reference
b) high CHO training

Answer 16

a) a greater level of training adaptations (i.e. mitochondrial biogenesis) - (Hawley & Burke, 2010)
b) better quality of training

Question 17

Describe how caffeine ingestion (how much?) before prolonged exercise effects performance and metabolic usage.
- give a reference

Answer 17

• 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).

Question 18

What are the mechanisms through which caffeine has an effect on the body?

Answer 18

> 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?

Question 19

What is a limitation into the findings of ‘train low’?

-reference

Answer 19

• Burke et al (2011)
  > reduced training intensity
  > no convincing evidence that train low strategies enhance performance over conventional methods.

Question 20

What is the theory as to why pre-exercise ingestion of solid CHO would be better for performance than liquid?
- reference

Answer 20

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)

Question 21

How does ingestion of solid vs. liquid CHO pre-exercise affect blood glucose conc, CHO oxidation and performance?
- reference

Answer 21

no difference in blood glucose conc, CHO oxidation rates (Pfeiffer et al (2010) or performance (Neufer et al, 1987)

Question 22

What did the Jeukendrup (2010) review conclude with regards to ingesting CHO before prolonged exercise?

Answer 22

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.

Question 23

How does CHO ingestion timing within (within the hour before) affect metabolic response?
-reference

Answer 23

• 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.

Question 24

What is the general consensus on whether ingestion of CHO during the hour before prolonged exercise benefits performance?

Answer 24

Research finds either no performance effect or a benefit (Sherman et al, 1991), despite elevated insulin levels and initial drop in blood glucose.

Question 25

How does CHO feeding just before warm up reduce some of the -ves of CHO before exercise?
-reference

Answer 25

Brouns et al (1989) found that giving ppts CHO drink during warm up followed by small break before exercise lead to no rebound hypoglycaemia, independent of amount of CHO ingested.
This is because exercise begins before insulin conc has increased.