Hi there -- this question has been asked here before a few times. Not discouraging further answers, but I present one of our favorite question/answer combos of all time:
A bit late to the party and this is not such as an extensive answer as was given in the other thread, but I wanted to mention that there is a work called Gymnasticus by Philostratus which is seen as the only surviving manual on athlete training in the ancient world. Philostratus offers an extensive catalogue of athletic body types, which is meant to reveal their suitability for particular events. A good trainer must recognise the natural abilities of an athlete and train him accordingly. He for instance mentions a Tetrad training technique, a four days cycle, where the first first day is for preparatory exercises, the second is a strenuous day of intense grueling training, the third is the day of recreation and rest, the fourth is a day of moderate training. Something that is not too dissimilar from some modern training practises. However, the text very likely has other aims than to provide training advise and is strongly influenced by philosophy. You can watch a talk on it here, if it interests you.
Additionally there's also a papyrus ( Papyrus Oxyrhynchus III 466) that is containing instructions for wresting, including the description of various grips and holds, but that again doesn't really mention nutrition as far as I know.