Running speed during training and percent body fat predict race time in recreational male marathoners Marathon runners are always wondering if about long legs or much muscles are crucial for a fast marathon period.We have studied with 126 male marathon runners, whether the sizes of extremities, skin fold thickness, weight, size, BMI, muscle mass, or training influence the marathon time.If you consider all the variables, only the body fat and the running speed remain in training at the end. So if you have little body fat and running fast in training, a fast marathon time will be achieved accordingly. These two variables correlate with each other, whoever runs quickly will reduce body fat, but also a deep body fat can promote a fast running speed.
With the formula 326.3 + 2,394 x body fat in percent - 12.06 x running speed in km / h you can predict the marathon time relatively accurately. The whole article can be found in https://pubmed.ncbi.nlm.nih.gov/24198587/