Just as today most participants of international contests in Antiquity were professional sportsmen. To enhance their chances of victory, they trained intensively in the gymnasion, under supervision of a professional trainer. Hard training and considerable self-discipline were the key to success in the international circuit.

The athletes trained to strengthen their muscles and to improve their technique. To exercise their muscles they used halters, the weights developed for the long jump, which could also be held in each hand while doing other exercises to develop arms and shoulders. For weightlifting they used heavier weights. According to an inscription, the weightlifter Bubon held a stone of 143 kg above his head with one hand and threw it away.

Also the technique of the sports had to be practised. Boxers did shadowboxing or punched a punching bag. Pankatiasts used a heavier punching bag, which they also kicked with their feet. Wrestlers looked for sparring-partners in the gymnasia. In Egypt, they even found a fragment of a wrestling manual on papyrus.

Professional athletes followed a strict training schedule, which was subject to fashion changes. About AD 200, several trainers worked according to the tetrad-method: a rigid schedule of four days in which the athlete did preparatory exercises on the first day, did a very heavy training on the second day, rested on the third day and exercised modestly on the fourth day. In Olympia the hellanodikai were apprensive of strange training methods. Therefore, they determined how the athletes had to train during the month of obligatory preparation.

One-sided and intensive training produced characteristic athletes like runners with muscular legs, but narrow shoulders, or fighters with a broad thorax but skinny legs. The doctor Galenus critizises this one-sided training and prefers the many-sided and more healthy exercise of the ball-game.