Week 9 Lecture - applied nutrition Flashcards
Main nutritional considerations for endurance sports
1) Fuel during exercise: CHO/fat/protein
2) Fluid requirements during/ post-exercise (due to prolonged sweating)
3) Post-exercise recovery: CHO/protein (due to daily training/ twice daily training)
Fatigue during prolonged exercise:
- Textbook views of fatigue have focused on the depletion of substrates or accumulation of metabolic by-products
- Widely cited causes of fatigue include substrate depletion, loss of body fluids, hyperthermia (cold drinks help modulate body temperature)
carbohydrate (CHO) intake recommendations for endurance athletes:
Light activity: 3–5 g/kg/day
Moderate activity (~1 hour/day): 5–7 g/kg/day
High activity (1–3 hours/day): 6–10 g/kg/day
Very high activity (>4–5 hours/day): 8–12 g/kg/day
Recovery after exercise (up to 4 hours): 1.0–1.2 g/kg/hour
CHO supplementation:
Providing CHO before exercise won’t meaningfully change muscle glycogen stores. However it does supply the liver with fuel.
- CHO ingestion before and during exercise has been consistently demonstrated to enhance performance in events lasting >60mins. Or events that rely almost entirely on muscle glycogen.
- Peripheral effects: glycogen sparing (liver or muscle), Maintenance of blood glucose, maintenance of CHO oxidation (more efficient to use CHO as a fuel than fat- using 100% CHO uses less o2 to than fat, so they will work at a lower vo2 max)
- Central effects: effects in the brain that are derived from CHO ingestion
CHO supplementation: before exercise:
- Ingestion of CHO <60min before the start of exercise has been discouraged
- Concern about consuming CHO very close to exercise due to rebound hypoglycaemia (slight drop in glucose) – this may have a negative effect on performance
- Rebound hypoglycaemia is not relevant to most athletes as the liver will release more
- If you are looking to optimise performance – there is no difference in the performance time achieved – therefore not necessary to consume glucose immediately prior
Placebo effect of CHOs?
- Water, placebo and CHO trials: cycle TT performance – 3hr TT performance
- 11% difference in performance
- No placebo effect when applying CHO during exercise – led to an improvement in performance
- In short duration exercise there may be psychological effects
CHO mouth rinse: This is a mechanism but not a strategy
- Placebo or CHO rinsed in the mouth (not swallowed) – cyclists TT trial
- 2.9% difference between CHO rinse and placebo
- This demonstrates a mechanistic way that CHO can influence performance
- Theory? Receptors in the mouth where the CHO interacts and send a message to the brain to say CHO is coming, so work harder/ faster (even if CHO is not delivered)
- Not a practical strategy? No reason to spit the CHO out – when you swallow it, there is greater performance effects
- Scenarios where it may be better to spit it out: if extra weight caused by drinking the CHO will affect performance e.g., an extra 50g could influence a high jumpers performance
- Or if you don’t want/ need the extra Kcals
- GI upset? However, 25-50ml of CHO will not cause GI upset. Putting calories into the stomach alleviates GI discomfort.
Train the gut?
- 28 day training with either high CHO or moderate CHO diet
- The ability to utilise glucose in drinks is increased when a high CHO diet is delivered
Recommendations for CHO intake during events:
< 30 minutes: No CHO required.
30–75 minutes: Very small amounts; possibly a mouth rinse.
1–2 hours: Small amounts, up to 30g CHO/hour.
2–3 hours: Moderate amounts, up to 60g CHO/hour.
>2.5 hours: Large amounts, up to 90g CHO/hour.
Post-exercise recovery: CHO intake guidelines
- Highest rates are achieved in the 2hr following exercise with the ingestion of high GI foods
Strength sports nutritional requirements:
- Training characterised by large amounts of resistance exercise and maximal strength exercise
- Aim to maximise muscle/ power-to-mass ratio
- Main nutritional considerations: energy balance, daily protein intake, protein timing around training
- CHO will still be important
Energy for strength sports
- Absolute energy requirements usually greater in strength than endurance athletes, but relative energy requirements are usually lower
- Due to greater body mass
Protein requirements for strength sports
- 20-25g sufficient for most meals to maximise responses
- Post exercises – 40g may be more beneficial
Source: whey>soy>casein
Timing: not important for protein response. sooner allows for more feeding opportunities
Common athlete focused goals:
- Achieve and maintain correct physique
- Meet the energy and fuel demands of training and competition
- Promote adequate hydration
- Promote recovery
