Marathon fueling: get it right, before, during and after

Over the past 30 years or so, a large body of research has accumulated showing that consuming carbohydrate while on the move (eg gels, carbohydrate drinks etc) can significantly enhance performance over longer-duration (90+ minutes) events. The explanation is simple and twofold:

1.      Carbohydrate is the muscles’ premium fuel during exercise because carbohydrate can be absorbed and broken down to release energy efficiently and rapidly.

2.      Due to the biochemistry of carbohydrate oxidation, more energy can be liberated per litre of oxygen consumed compared to fat. That makes carbohydrate the best fuel for meeting the energy demands of muscles when exercise intensity becomes very high and when oxygen is scarce (because you are at or near your maximum oxygen uptake limit  - also known as ‘VO2max’).

Much of the carbohydrate oxidized for fuel during exercise is derived from stored carbohydrate in the muscles (muscle glycogen). Research shows that even a modest drop in the levels of muscle glycogen can produce feelings of fatigue and tiredness, which is why a large body of research has demonstrated that keeping topped up with carbohydrate during prolonged exercise can help stave off fatigue^(1-9). It’s for this same reason (to top up your muscle glycogen) that sports scientists recommend a triple-whammy approach to fueling for an endurance event and for superior recovery after an event. This approach is as follows:

·        Pre-event fueling - Ensure that you consume plenty of carbohydrate in the days leading up to a big event such as a distance ride, running marathon or longer-distance triathlon (sometimes referred to as ‘carbohydrate loading’, which you can read more about the theory and practice of carbohydrate loading in this article). Additionally, researchers have suggested that in the hours prior to an event, athletes consume pre-exercise protein intake at around 0.3 grams per kilo of bodyweight (depending on gastrointestinal tolerance) in order to help offset the significant muscle breakdown that can occur during a race, particularly in running events⁽¹⁰⁾. Regarding pre-race fat intake, athletes should limit high-fat foods to avoid GI discomfort.

·        In-race fueling - a large body of research has established that in-race carbohydrate fueling can prolong endurance performance. Recent data suggests that a good rule of thumb is as follows (see figure 1)⁽¹⁰⁾: for events lasting less than 60 minutes, no carbohydrate ingestion is required; for activities lasting over 60 minutes, an active fueling strategy is recommended to maximize performance and that when events last 60-150 minutes, athletes should consume 30–60 grams of carbohydrate per hour, using a 6–8% solution (concentrations typically found in commercial sports drinks); for events lasting over 150 minutes, higher carbohydrate intakes of 60–70 grams per hour up to 90 grams per hour (if tolerable) can give improved performance, ideally consumed every 10–15 min to maximally spare glycogen stores; at the highest levels of intake, multiple transport carbohydrates – ie glucose/fructose drinks and gels – are recommended for easier absorption (see this article for a more in-depth look at carbohydrate type).

·        Post-race fueling - Post-exercise carbohydrate consumption continues to be a very important nutritional strategy, as it is essential to speed recovery. Research shows that consuming 0.8–1.0 grams of carbohydrate per kilo of bodyweight per hour following exercise results in higher replenishment of glycogen stores⁽¹¹⁾. Additional research indicates that the addition of 0.3 or more grams protein per kilo of bodyweight per hour can also be beneficial for enhancing glycogen resynthesis and promoting muscle synthesis to compensate for muscle tissue loss during exercise⁽¹⁰⁾. Furthermore, it is recommended to replace fluid loss by consuming water or hydration drinks equivalent to 150% of the pre-post bodyweight lost⁽¹⁰⁾. For example, if you lose 1kg of bodyweight as a result of exercise, the recommendation is to consume 1.5kgs (ie 1.5 litres) of fluid in the hours after exercise.

Figure 1: Summary of carbohydrate intake recommendations by event duration