Several years before canon a meteor almost fell to earth but was sucked into a black hole and taken to another universe.
(currently)
see you god
He was doing things like if you practice race-limited body control the human body can only contract and retract to a limited extent the god has been stretching every single day throwing 800 punches in the air every single day throwing 800 kicks in the air every single day he too he had been doing an 80 km run every single day everything so that his body had the best physical condition on this planet soon after dio created his own stone mask using instant mastery to master the creation of a stone mask it exists at joestar mansion but the god doesn't want to steal it
He has been training his senses his strength his speed and flexibility not only that but he also lives eating lots of tomatoes and various other foods that can be used to resist solar radiation
He has also been training his regeneration every single day flexibility prevents injuries prevents back pain improves athletic performance prevents balance problems and increases blood circulation in the body in addition to relieving tension
And all this helps when becoming a vampire as it increases the potential of the human body.
Timeskip ???
Dio has developed the maximum flexibility that a human can achieve, has a basically perfect physique in addition to having well-defined phantom blood-style muscles.