New lifters get stronger at a movement by doing similar big exercises, even if they don’t do the exact movement, because their brain learns to move better.

In untrained individuals, compound movements can improve performance on isolation movements due to enhanced neuromuscular coordination, overriding the specificity principle; however, in trained individuals, strength gains are highly movement-specific.

Whether you train with one joint (like leg extensions) or multiple joints (like squats), you get just as strong at the movement you train — but if you train a simple movement, you get a bit stronger at holding still too, compared to complex movements.

Lifting lighter weights many times until you can't do more builds muscle strength just as well as lifting heavy weights a few times until you can't do more, for people who already work out.

Lifting heavy weights for just a few reps makes you stronger in exercises that work one muscle at a time, more than lifting lighter weights for many reps, especially if you already work out regularly.

Strength expression is highly movement-specific, but in untrained individuals, neuromuscular adaptation from compound movements can produce greater strength gains in target movements than direct practice due to enhanced motor unit recruitment and coordination.