CARBOHYDRATES (CHO) CONSUMPTION DURING ULTRA-MARATHONS: 60, 90 OR 120 GRAMS/HOUR?

Ultra-endurance events (> 4h), especially in mountainous terrains, have become very popular in recent years. Runners in these events are exposed to various topographic, climatic, altitude and temperature conditions.

The demanding racing conditions carries extreme physiological demands. Among them we could highlight negative energy balance, dehydration, decrease in blood glucose levels, glycogen depletion, exercise-induced muscle damage (EIMD) and inflammation.

Carbohydrates (CHO), as the main substrate of muscles, plays a key role in preventing fatigue, being it peripheral (muscles) or central (central nervous system).

After exhaustive exercise bouts with glycogen depletion high CHO diets are required for periods up to 48h to replenish glycogen depots (liver and muscles). If there is also EIMD, as in most ultra-endurance events, this recovery period may extend up to 10 days.

During endurance exercise CHO intake is known to delay neuromuscular fatigue and improve exercise performance. Current recommendations for ultra-events lasting more than 2.5h is 90 g/h, although the usual intake of athletes is around 60 g/h.

A recent study has compared the results of different levels of CHO ingestion (60, 90, or an over-recommended dosage of 120 g/h) on the performance and post-race muscular function and recovery.

 

The study

Twenty-six elite trail-runners participating in a mountain marathon (Oiartzun Marathon, Spain, 4000 metres of cumulative slope) were randomly distributed in three groups with different CHO intakes: LOW (60 g/h), MED (90 g/h) and HIGH (120 g/h) with a 2:1 glucose/fructose ratio. Runners had no injury, disease or were taking any medication.

Neuromuscular function was evaluated using an Abalakov Jump test (x3 vertical jumps with 30s breaks) and a half-squat test (one repetition at maximal weight, followed 5 minutes later by 3 repetitions at maximal speed and 70% of maximal capacity).

Aerobic power capacity was evaluated through a VO2max test, performed on an ergometric tape (constant speed of 20 km/h and 1% slope) measuring time until exhaustion.

Measurements were done at baseline (T1) and 24h after completing the race (T2). Athletes followed a personalized diet (9 g CHO, 1.5 g protein and 0.5 g fat per kilogram of body weight and day) from 48h before the race until 24h after completion.

 

The results

There were found changes in Abalakov jump height and half-squat maximum between T1 and T2 in groups consuming 60 and 90 g CHO/h, but not in the group consuming 120 g CH/h.

In the Abalakov jump test the group consuming 120 g CHO/h had a better response 24 h following the mountain marathon race than the runners consuming 60 g/h or 90 g CHO/h.

Regarding high intensity run capacity, runners that consumed 120 g CHO/h during the mountain marathon showed higher lactate production and better performance in the aerobic power-capacity test carried out 24 h after the race.

No significant improvements in overall race performance, although runners ingesting 120 g CHO/h tended to faster times.

 

Conclusions

  • Consumption of 120 g CHO/h is possible without serious gastrointestinal problems.
  • Endurance athletes can train the gut to improve CHO intake, digestion, absorption and utilization during exercise.
  • Higher CHO intake during exercise could be an enhancing performance strategy, but also a tool to optimize long-term recovery and help in multi-stage competitions.

 

Bibliography

Effects of 120 vs. 60 and 90 g/h Carbohydrate Intake during a Trail Marathon on Neuromuscular Function and High Intensity Run Capacity Recovery. Urdampilleta A, Arribalzaga S, Viribay A, Castañeda-Babarro A, Seco-Calvo J, Mielgo-Ayuso J. Nutrients. 2020; 12(7):2094.

Pre and post-race tests (from Urdanpilleta et al. 2020)
Race fueling protocol and timing (from Urdanpilleta et al. 2020)

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