Pushing an immovable load versus holding one in place
An overcoming isometric is an effort exerted against a fixed, immovable resistance: pushing or pulling on pins, a strap, or a wall that will not move no matter how hard you drive. Because nothing yields, the muscle works at a near-constant length while you ramp intensity up toward a voluntary maximum. A yielding isometric is the opposite intent: you support an external load (your bodyweight, a barbell, a dumbbell) and resist it from moving, holding a fixed joint angle for time until fatigue.
The practical cue is direction of intent. Overcoming means trying to move something that cannot move. Yielding means trying not to be moved by something that is pulling on you.
Why the two styles tend to drive different adaptations
Overcoming isometrics let you reach high voluntary force quickly and are often used to train rate of force development and to push force output at a specific sticking-point joint angle. Yielding isometrics emphasize time under tension and positional endurance, and they appear in tendon-loading and rehabilitation contexts where a controlled hold is tolerated when dynamic work is not.
Strength gains from isometric training are most reliable near the trained joint angle, with limited carryover to angles far from it. Treat this as general educational information rather than a prescription; loading, joint position, and progression should be set with a qualified coach or clinician, especially during injury rehabilitation.