A cyclist spends a lot of time on a bike and the way he sits and pedals on the bike is very important.
Having the right position and choosing a bike that suits the athlete have a big impact on performance. The position kept could be wrong, the saddle could be too high, the handlebar could be too far or the bike could just be too big or small.
For this reason there are several tools and applications to determine bike fit and an entire research area covers this topic that is biomechanics.
One of the tool used by pro cyclists is Retul. Another is Guru.
But there are other applications that provide bike fit information. Kinovea provides video analysis and it is a free open source application. An an iOS application, compatible with iPhones and iPads, is Bike Fast Fit
You are going to spend a lot of time sitting on a bike, better doing it correctly and comfortably. The tools exists and are also affordable.