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Planning to do a marathon? A new way of analysing data from a smartwatch could help forecast how you will perform.

鈥淢arathon prediction is very difficult,鈥� says at the French National Centre for Scientific Research (CNRS), but he and his colleagues have developed a more accurate mathematical model to do the job.

Currently, most smartwatches estimate the wearer鈥檚 VO₂ max 鈥� the maximum rate at which they consume oxygen during exercise 鈥� via heart rate measurements and use this estimate to predict their race times. But using a single parameter to do this isn鈥檛 very accurate, says Emig, and can result in errors of up to 20 per cent.

鈥淭hese errors are very large,鈥� says Emig. A 20 per cent faster marathon time could be the difference between a pace of 4 minutes per kilometre versus 5 minutes, he says. 鈥淭his is a lot.鈥�

The team鈥檚 mathematical model instead uses smartwatch data to calculate two physiological parameters 鈥� the speed a runner has at maximum oxygen uptake and the rate at which they lose power during a race. The former is directly related to a person鈥檚 VO₂ max, whereas the latter is linked to their endurance.

The researchers tested their theoretical model using smartwatch data from about 14,000 runners, ranging from recreational runners to elite athletes. Using their calculations of the two physiological parameters, they were able to predict people鈥檚 marathon times to within 10 per cent of their actual time, on average, and to within less than 5 per cent of the actual time for elite athletes.

鈥淭his is a very good prediction of such a complex end-point of marathon racing time, which is also influenced by numerous data not taken into account by the smartwatch, such as changes in elevation, type of terrain the marathon is run on [and] environmental conditions,鈥� says 艁ukasz Ma艂ek at the National Institute of Cardiology in Warsaw, Poland.

Ma艂ek says more realistic predictions of race time could also help runners to better plan their training and potentially reduce the risk of overtraining. 鈥淚t may limit the risk of potentially life-threatening incidents, which are more likely to occur during supramaximal efforts, especially in athletes trying to meet unrealistic expectations,鈥� he says.