It doesn’t take a sports scientist to observe that distance runners tend to be on the lean side. Excess body fat adds to the weight that has to be carried from foot to foot, and thus increases the energy cost of running – without contributing anything useful, in physiological terms. What’s more, research suggests that losing excess body fat aids performance, even in the absence of improvements in other physiological parameters. For example, I weighed 58kg when I ran my 1 hour 32 minute half marathon a few weeks back. Now (following interrupted training due to my troublesome plantar fascia and the
fact that I am now tapering for the marathon – oh, and a few too many cupcakes) I weigh 60kg, for which my predicted finish time for a half marathon would be 1.34.44 – 2 minutes and 44 seconds slower. If, on the other hand, I were to get down to 56kg, my predicted time woud be 1.29.15 – a useful 2.45 minutes faster than my PB. But of course, weight loss is only potentially performance-enhancing if it doesn’t take you beyond the realms of a healthy weight, in which case the negative effects of being underweight (increased fracture risk and inadequate energy supply, for example) will outweigh any benefits.
But there is another way you can shave off ounces and potentially improve performance – slim down your race kit! Heavy jogging bottoms and hoodies can add at least 0.5kg to your racing weight, while one study found that every 100g of shoe increased aerobic demand by 1 per cent – so opt for the lightest trainers you feel comfortable in. And go easy on the carbo loading!