When it comes to hard training, the importance of adequate carbohydrate to keep your muscle stores topped up cannot be overstated. But how much, when and what types are best? Andrew Hamilton looks at what the science says MORE
Race fueling: start early, fuel little, fuel often
Andrew Hamilton looks at new research on race fueling and explains why endurance athletes might need to rethink their fueling strategy
Over the past 25 years or so, there’s been a bucket load of research showing that consuming carbohydrate while on the move (eg gels, carbohydrate drinks etc) in the saddle can significantly enhance performance over longer-duration (90+ minutes) events. The reason is simple: carbohydrate is your muscles’ premium fuel during exercise because carbohydrate can be absorbed and broken down to release energy efficiently and rapidly. And due to the biochemistry of carbohydrate oxidation, more energy can be liberated per litre of oxygen consumed. That makes carbohydrate the best fuel for meeting the energy demands of your muscles when your 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’).
Muscle glycogen and fueling on the move
Much of the carbohydrate oxidized for fuel during exercise is derived from stored carbohydrate in the muscles (muscle glycogen). It just so happens that even a relatively 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 also recommend 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. This approach is commonly referred to as ‘carbohydrate loading’ (you can read more about the theory and practice of carbohydrate loading in this article).
Fueling on the move strategy
As mentioned above, a large body of research has been conducted on carbohydrate fueling during exercise to prolong endurance. But what is the ideal strategy for you to use? A comprehensive review study (one that pulls together data from a number of other studies on the same topic) published last year concluded the following(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.
- For events lasting 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).
Figure 1 summarizes these recommendations visually.
Figure 1: Summary of carbohydrate intake recommendations by event duration
Carbohydrate intake frequency
From the data above, you might conclude that consuming carbohydrate for the first hour is unlikely to produce any performance benefits, but that once exercise extends into the second hour, carbohydrate at the recommended level should be consumed four or five times per hour. Ask many endurance athletes how they fuel their events and this is likely to the kind of thing they often report. However, the timing and frequency of carbohydrate ingestion during exercise is not a very well researched topic, and the few studies that have been carried out have been mainly confined to cycling. But now new research suggests that this approach may not be optimum, especially for events lasting over 75 minutes or so.
Very little, very often
In this study, British scientists set out to establish whether feeding carbohydrate early, and in very frequent but small doses, was more effective at prolonging endurance in runners than feeding same amount of carbohydrate later during an exercise bout, in a larger dose(11). Six well-trained runners underwent two trials in which they were fueled with carbohydrate during the first 75 minutes and then went on running until the point of exhaustion was reached. The two trials were identical except in the way the carbohydrate drink was consumed in each trial:
- *Trial 1: No carbohydrate for the first 75 minutes; 75g of carbohydrate ingested at the 75th minute into exercise.
- *Trial 2: Carbohydrate (75g in total) consumed from the start with runners consumed 5 grams at 5-minute intervals.
There were three key findings:
- When the runners underwent trial 2 (consuming carbs every five minutes from the word go), they used less muscle glycogen during the first 75 minutes than in trial 1.
- Consuming 5g every 5 minutes enabled the runners to extend their endurance – ie they were able to run for longer before becoming exhausted.
- There was a modest correlation in the amount of glycogen sparing and the delay in exhaustion; runners with the lowest use of muscle glycogen during the first 75 minutes tended to have to longest times to exhaustion.
The study authors were clear about their take-home message for runners. They concluded thus: ‘This study indicates that failure to ingest carbohydrates from the outset of prolonged running increases reliance on limited endogenous muscle glycogen stores – the effects of which cannot be rectified by subsequent carbohydrate ingestion late in exercise’. In other words, athletes should start consuming carbohydrate during exercise IMMEDIATELY and regularly (possibly as frequently as every five minutes) to maximize endurance later in the race. Consuming more carbohydrate later on in your event will NOT compensate for not consuming any early on because some muscle glycogen depletion has already occurred.
Implications for endurance athletes
This study suggests that delaying feeding carbohydrate from the very outset might harm your performance later on in the race. It also suggests that no amount of ‘extra’ carbohydrate can compensate for the extra muscle glycogen used earlier in a race due to not feeding. It also suggests that very little and very often is an appropriate strategy for these early stages – the part of the race when most athletes won’t particularly feel the need to consume carbohydrate. Another important implication is that (because muscle glycogen stores are critical) all athletes MUST come to the race fully fueled and topped up with muscle glycogen(12). This means ensuring that you not only taper properly before an event, but you also ensure your carbohydrate intake in the days leading up to the race is ample. That’s another story of course, and one you can read about here!
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