Anything 3 and up is in the realm of normal function.
The range for PC strength is 3-18. Thus a character with a strength of 3 might be a weakling who cannot effectively wield a weapon or move with any speed in armor, but they are capable of normal human function. In other words, dressed in normal clothing, such a character can move around without difficulty and manipulate lightweight objects without any trouble. Such a character might even be incredibly healthy (high Constitution). Imagine a very short, very petite person who does no strength training. They might struggle to lift a 10 pound barbel off the ground (10 pounds is severe encumbrance for strength 3 in AD&D 2e), but still might be capable of running a marathon. The strength stat means brute muscle power only--there are simply things that the character cannot lift, push, wield, or wear. They can try, but they'll fail. The narrative ramifications don't really go beyond that.
Someone who was wearing armor and got reduced to a Strength score that would not permit them to bear a load as heavy as the armor itself would probably collapse and then have to struggle out of the armor. If they had a heavy sack over their shoulder, they'd likely drop it or it might even pull them backwards off balance and cause them to fall. Someone who had a natural strength so low would never have put the amor on or hefted the sack to begin with. Regardless, once the sword or sack was dropped and the armor was shed, the character would be able to move and act normally, but they'd just be less capable of lifting, pushing, dragging, etc. Since Constitution covers stamina and Dexterity covers agility, the narrative implications end at these simple limitations on brute strength.
2 and lower gets into the realm of abnormally weak and not being able to function.
Barring magical or other such effects, strength scores below 3 are indicative of some kind of physical abnormality--not possible in a Player Character. Once a strength score drops this low, you, as the DM, need to start considering more severe implications, like the character's legs no longer being able to support their weight or the character being unable to effectively use even light weapons or tools. As DM it's up to you exactly how the character is impacted, but the AD&D 2e Encumbrance Tables should be your guide. A character with a strength of 2 cannot carry more than 6 pounds and the rules assume that clothes weigh 5 pounds. Clothes alone put a character with a strength of 2 into the severe encumbrance category--movement reduced to 1, To Hit penalized at -4 (stacking with low strength penalty) and AC penalized at +3... basically helpless. A character with a strength of 1 is not even accounted for on the encumbrance tables, which could mean they can barely function at all beyond lying in a bed.