Does this mean that you will get the most benefit from your marathon training if you never use a sports drink during workouts? It does not. In 2010, a team of Australian researchers compared the effects of habitually training with and without a sports drink on fitness gains over a period of 28 days in a group of 16 trained cyclists and triathletes. The researchers found that performance in a cycling time trial increased equally—roughly six percent—over four weeks regardless of whether an athlete used a sports drink in every workout or none.
This finding might seem to suggest that it doesn't matter whether you use a sports drink or not in your training—either way you'll gain the same amount of fitness. But I don't think that's the case, because the Australian researchers also found that training with and without a sports drink increased fitness in somewhat different ways. When the subjects trained with a sports drink, their muscles got better at burning carbs. But when they trained without a sports drink, their muscles got better at burning fat. This indicates that the benefits of training with and without a sports drink may be additive to some degree.
In other words, if your fitness is likely to improve by six percent in four weeks if you always train with or always train without a sports drink, your fitness may increase by eight or nine percent if you train with a sports drink in some workouts and without a sports drink in others.
So where does this leave us? I now recommend that runners use a sports drink in roughly half of their runs lasting between one and two hours, and drink only water in the rest. This way you get the best of both worlds: better performance resulting in bigger gains in carb-burning capacity in runs with a sports drink and a greater challenge resulting in bigger gains in mitochondria and fat-burning capacity in runs without a sports drink. When you run longer than two hours, I still think it's best that you use a sports drink every time in order to prevent glycogen depletion from becoming too severe. For additional guidelines on how to fuel your training runs, check out The New Rules of Marathon and Half-Marathon Nutrition.
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