What kind of changes occurred in the Roman military to armor and training techniques?

Most important changes occured during reforms of gaius Marius mostly in organization of army making it fully professional force changing in training was based on gladiator way of fighting but modified to formation, main change in armour was adding the lorica segmentata armour made from thick iron and lether plates

The Romans were well known for their ever-adapting military machine. They would adapt the useful things from certain nations they conquered and would take out the ones they didn't consider to be useful from their own military structure. This enabled the Roman conquesting force a good portion of flexibility through time.