Importance of Carbohydrates
Carbohydrates are a main source of energy in the human diet, and as such research suggests increasing dietary carbohydrate intake can improve high intensity exercise performance.
Muscle glycogen and blood glucose are important substrates for contracting skeletal muscle during intense exercise yet fatigue often occurs from a depletion of carbohydrate stores. During cycling, glycogen depletion is seen in the Vastus Lateralis, from fatigue causing insufficient ATP Resynthesise, impairing blood glucose production and oxidative metabolism
Carbohydrates for fuelling an Ultra endurance event
Case studies investigating Ironman Triathlon events highlight carbohydrates are the most ingested source of energy during the event (75%). The cycling discipline composes 54% of the total race time for competitors, and therefore provides an essential opportunity to re-fuel and hydrate in the lead up to the marathon run to finish.
Athletes consuming optimal carbohydrates, relative to their body mass during the event can optimally conserve muscle and liver glycogen stores for later stages of the race in addition to endogenous sources, such as CHO gels.
Nevertheless, one issue proposed is the athlete’s inability to consume sufficient energy from carbohydrates, to sustain large energy requirements during the event, to prevent performance decrements.
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Carbohydrate intakes during cycling events
Carbohydrate intake 1-4 hours prior to a cycling event is recommended at 1-4 g.kg, in the form of low GI carbohydrate sources to provide maximal sustained fuel sources for later stages of the event where carbohydrates cannot be consumed.
During the event, up to 90.g.h of carbohydrate is advocated for improved performance. One explanation infers, higher carbohydrate oxidation will be achieved from products with multiple transporter CHO (glucose: fructose) during events.
Post event, 1-1.2 g.kg.h is advised immediately following the event, to maximise the replenishment of glycogen stores, as such carbohydrate rich meals. Recent research has shown there are no significant differences between male and females CHO intakes post event, as long as intakes are relative to body mass.
Additional nutritional considerations
Protein and fat intakes are ingested at smaller quantities during events to ensure CHO intake is not compromised and impairing performance.
Female and male protein and fat intake data reported over the duration of an Ironman triathlon event from Kimber et al., (2002) reported the following intake values;
Protein intakes were 55g for females and 45g for males
Fat intakes were reported at a mean of 9.7g for females and 8.2g for males during the race.
Fluid balance strategies
Additionally, during events CHO energy gels, and sodium rehydration fluids are commonly used to maintain fluid balance and minimise heat stress and dehydration symptoms.
Sports electrolyte drinks and highly concentrated CHO drinks are commonly used to offset sweat loss and prevent dehydration during events.
Consumption of 1.5 g/kg/BW/H CHO during the cycle discipline of the Ironman triathlon event is suggested optimal for maintaining fluid balance.
Rehydration fluids containing 1 g.h sodium is recommended for endurance events >4 hours.
Take away messages
- Optimal nutritional intervention & hydration for fuelling an endurance event is essential for maintaining sufficient muscle glycogen resynthesis, recovery & enhanced performance.
- Pre event, athletes may choose compact carbohydrate-rich sources that are low in fibre and easily consumed to ensure that fuel targets the gut and GI comfort are met.
- During event, higher carbohydrate intakes are associated with improved performance, as such sports drinks and CHO gels.
- Post event, there are no significant differences between male and female CHO intakes when relative to body mass, 1.0-1.2 g/kg is recommended for replenishment of glycogen stores.