It really worked well. USUALLY, I can go three to four times longer than I could before. Boxing is a sport which requires plenty of stamina. But unlike other athletes, boxers are always watchful krygen xl of their weight. A good diet is an important aspect of a good training regime. Poor diet can strain off the energy in the ring and drain off the muscle strength. A nutritious diet is required to provide the stamina needed for high levels of energy that the ring demands.