I got the 23andme health test results and there was a report about muscle composition. It said that there were 3 gene variants that affect power generation capability and that I had a variant that was common in elite power athletes (sprinters, jumpers, and throwers). I got all excited until I looked more closely at the data and discovered that 2 of the 3 variants are common in elite power athletes and that 80% of European heritage 23andme customers have genes with this variant. So, that, in combination with not data about endurance genetics, means, in the end, these kinds of sites are not very useful for predicting performance.
Steve