Endurance athletes can lose up to 3-4% of their body weight during a race, this means getting your nutritional intake and hydration strategies right is paramount, if not it can result in dehydration, increased fatigue, cognition dysfunction and poor performance. However, many runners especially at the recreational level often overlook the importance of refuelling and in many cases have suboptimal carbohydrate intake levels. This creates an environment for “hitting the wall” which occurs in over 40% of runners.
This catastrophic failure resulting in severely impaired performance occurs because runners have failed to maintain sufficient carbohydrate (CHO) intakes levels, resulting in a depletion of their CHO stores (glycogen). Runners try to overcome this through “carb loading” however, glycogen stores in the muscles and liver are relatively small compared to fat stores. These glycogen stores are rapidly depleted primarily by aerobic capacity (VO2Max), especially in the untrained runner, as aerobic capacity involves energy rich physiological functions such as cardiac output and ventilation. As such, the role of CHO intake during running is to improve performance by preventing low blood sugar levels (hypoglycaemia), maintaining high levels of CHO’s for energy production (CHO oxidation) and increasing endurance capacity.
The actual CHO intake levels a runner requires for optimal performance is individualised and determined by multiple factors such as level of fitness, terrain, heat, altitude etc with distance or time spent running being the primary factor. A marathon can take anywhere from 2 to 6 hours to complete with nutritional intake varying depending on the length of time one is running for. The current CHO intake recommendations for those running for 2-3 hours is 60g/hr, while those who are running for longer than 2.5 hours need to be ingesting 90g/hr.
These may seem like high and unachievable numbers especially to those who might only take on one or two gels (20-40g) over a 3-4 hour race. Additionally, if one were to rapidly increase their CHO intake from such low levels to 60-90g/hr they would most likely experience stomach irritation. As with training load, increasing CHO intake load must be trained and increased incrementally to tolerate the higher levels. This is best achieved during training where one can manipulate different combinations of fluids and gels to find the strategy that works best for them. It is also important to set realistic goals, if the current intake is 20g/hr yet it should be 60g/hr and the marathon is in 6-7 weeks achieving 60g/hr in that time frame without experiencing stomach irritation is unrealistic, a more realistic target might be 30-35g/hr.
However, not everyone can achieve the recommended levels of CHO intake no matter how much they train, while other runners will have intolerances to certain types of glucose (sugars), usually fructose. In these cases there is research that shows CHO mouth-rinsing (rinsing but not ingesting) improves endurance performance and can provide an alternative or help supplement ones achievable CHO intake levels. CHO intake during prolonged exercise is important to prevent CHO and glycogen depletion and to maximise performance, so to avoid hitting the wall on your next marathon run make sure you consider the importance of CHO intake in your marathon preparation and race.