How to Bend Strings Correctly
A bend looks like a single finger moving, but the strength actually comes from the whole hand and forearm - the finger just holds the string while the wrist does the pulling. That's exactly why a bend done with 'just one finger' tires the hand out fast and often falls short of the target pitch.
Where the strength comes from
The finger pulling the string shouldn't work alone - it's backed up by the neighboring fingers behind it on the same fret, and the motion itself comes from rotating the wrist, like turning a doorknob, not from bending a single joint. That's the only way to reach a full-step bend without excessive strain or risking snapping the string off the fret.
Which finger does the pulling
For a whole-step bend or bigger, the ring finger is the usual choice, backed up by the middle and index fingers behind it - the ring finger or pinky alone don't have enough strength for an accurate bend without over-straining the wrist. The pinky is usually left for smaller half-step bends, which need less force.
Which direction to pull
On the lower (thicker, bass-side) strings it's easier to pull the string down, toward the floor; on the higher strings, up toward the ceiling - in both cases the finger pushes the string toward the neighboring, narrower part of the neck, where it's easier to maintain pressure. Pulling the opposite way is physically possible but needs noticeably more force for the same result.
Thumb support
The thumb hooked over the top edge of the neck is the second anchor point, without which all the strength goes into just holding onto the guitar rather than into the bend itself. It's the same anchoring principle that matters for clean chords too (see the article on thumb position).
How to train it
Start on the lower frets (the string is physically stiffer there) with a half-step bend - only move to a whole step once the wrist motion feels natural. Pulling on the upper frets right away, trying to 'play it like the song', is a common reason a bend stays tense and imprecise.
Try it in practice
Open exercises