Restoration magic and healing potions can be used to restore any damage taken (thus one can also level up the Restoration skill simultaneously). If you have a shield of the appropriate armor type, one can also upgrade the block skill as well during this process. Mudcrabs are useful in this regard, as they have low health yet can do enough damage, especially the larger varieties.

One can rapidly level up the skill simply by finding an enemy (or group of enemies) which uses physical attacks and allowing them to attack without attacking back. Conversely increasing armor rating does not decrease the rate at which the skill advances. Being the victim of power attacks likewise grants more experience than a standard attack. Thus, taking multiple attacks from a skeever or wolf levels heavy armor at a significantly slower rate than blows from Giants or Mammoths would. Leveling up armor skills is relatively simple: take physical damage in combat while wearing armor pieces of that type. To level up the Heavy Armor skill most efficiently, wear a full set of Heavy Armor (head, hands, feet, chest). The rate of skill gain is based on the total amount of damage incoming before armor is applied.

Max armor rating skyrim