At the Heart of the Abyss
Shields are similar to Health, in that they are a pool of points that absorb damage. Shields regenerate in combat slowly, and always fully snap back to full after combat unless the character’s armor was somehow damaged. Well equipped soldiers in the Mass Effect universe don’t start worrying too much about being hit until that damage breaks through their shields.
Shields are also useful for keeping things at arm’s length. Darts laced with toxins, biotics that attack the neural system, and other things that require the attack to actually hit the character are ineffective if they can’t break past the shields. This makes them an excellent defense in combat, just as abilities that break down shields are prized.
While it’s true that shields are designed to activate in response to fast moving impacts, this includes melee attacks in addition to firearms. Any attack that can hurt a trained soldier wearing armor is moving fast enough to trigger a shield.
Shields do not block attempts to grapple the wearer, however, as they cannot stop a slow or determined attempt to grab the person they are protecting. They also cannot stop especially broad impacts like contact with the ground at the end of a fall. Damage inflicted by throws, falling, and environmental conditions like fire and radiation go straight to Health, bypassing Shields.
Shields that can recover in combat need some time to get going. The device starts diverting power to a capacitor, but it can only do that if the shields aren’t under attack. Otherwise, all power goes to keeping up the defense. Taking cover is essential to having one’s shields recover. If possible, it’s best to stay in Full Defense behind cover so there’s no possible way to get hit.
If the character can manage to go an entire round without suffering a hit, his shields recover at the end of the following round. It takes two full turns for the generator to build up the capacitor and boost the shields. The recovery is dramatic though. 50% of the shield’s total protection is recovered, rounded up. If the character wants to stay behind cover for one more round (or is just lucky and isn’t hit), going three full rounds without being hit, then the rest of the shields recover, bringing him up to full.
Of course, if his shields were at 50% or better when he took the time to regenerate them, then the first big boost will fill the shields up entirely.