Morrowind:Encumbrance

Encumbrance is the total amount of weight you are currently carrying, which applies to all items in your inventory, regardless of whether or not they're equipped. If you carry more than your maximum Encumbrance, you will be unable to move although you can still fight, cast spells and use items. Your maximum Encumbrance is equal to your Strength × 5. Once you have maxed out your Strength attribute, your maximum Encumbrance will be 100 × 5 = 500.

Encumbrance negatively affects the rate at which your Fatigue drains while running, the distance and height of your jumps, and your movement speed. The severity of these effects are based on the ratio between your current and your maximum Encumbrance. You can use Fortify Strength to increase your maximum Encumbrance or Feather to lower your current Encumbrance.

However, although both effects have the same base cost, a single point in Strength is equivalent to 5 points in Feather. Considering that increasing your Strength also also results in higher damage with weapons, Fortify Strength is usually the more favorable of the two. On the other hand, only Feather can bring your Encumbrance to zero, which allows you to move considerably faster and run further before you are completely fatigued as well as jump much higher and much further. Fortify Strength can only lower, but never zero out your current-to-maximum Encumbrance ratio.

Encumbrance can be increased by the Burden spell effect. Enemy spellcasters may use this on you and, if you are carrying a lot of items, you may find yourself stuck in place. This is especially dangerous if your combat abilities are limited to melee weapons. You may also use Burden on your foes, however, most enemies in the game are not carrying anywhere near their maximum Encumbrance; it would take a high-magnitude Burden effect to disable them to the same degree.

Likewise, maximum Encumbrance can be lowered by either damaging or draining Strength. The former has the advantage of being permanent, in addition to lowering their melee attack damage, however, the latter has a lower base cost in exchange for being a temporary effect. These effects may not be of much help against enemies who cast spells or fight using ranged weapons. The Paralyze spell effect disables attack, movement and spellcasting but at a much higher cost.