Specific Adaptation to Imposed Demand
The SAID principle, short for Specific Adaptation to Imposed Demand, states that the body adapts precisely to the kind of stress you repeatedly apply. Train heavy low-rep work and you build maximal strength. Train fast light work and you build speed. The adaptation tracks the demand closely, which is why a marathon runner and a sprinter develop very different qualities despite both running.
Specificity applies across several dimensions at once: the load used, the range of motion trained, the contraction speed, and the joint positions emphasized.
Why carryover is narrower than it feels
Strength gains tend to be most expressed near the angles, speeds, and patterns you practiced. Improving force at one joint angle does not guarantee equal improvement at distant angles, and getting stronger in a partial range gives the most reliable benefit within that range. This is the rationale behind training movements that resemble the target task, a concept coaches call transfer of training.
Specificity is a useful planning lens, not an absolute rule, since some general strength carries over broadly. This is general educational information rather than individualized programming advice.