You are staring at your program, counting exercises per muscle group. Leg press covers quads. Bench covers chest. If each muscle gets enough hard sets, the specific exercise delivering those sets should barely matter.
Total muscle growth from any single exercise matches growth from any other so closely that the difference disappears into noise. A review combining several direct comparisons confirmed it: the difference between exercise types was so small no measuring tool in a gym could pick it up. One exercise, done hard enough and long enough, grows the muscle.
That answers the size question. But the word in your search was not size. It was complete.
Do You Need Multiple Exercises per Muscle for Complete Development?
Complete development of a multi-headed muscle requires more than one exercise. A within-participant trial found that leg extensions grew the front quad nearly twice as fast as leg press, while leg press grew the outer quad three times faster than extensions. Total growth was identical — the difference was entirely in where the muscle grew.
— Burke et al. 2024 · Journal of Science in Sport and Exercise · n=28
A trial answered this with one of the cleanest designs in exercise science: each participant trained leg presses with one leg and leg extensions with the other. Same person, same effort, same training block. When the scans came back, the front of the quad had grown 8.9% with extensions but only 4.7% with leg press. The outer quad reversed: 8.7% growth from leg press, just 2.9% from extensions.
Same person. Same effort. Opposite regions.
The muscle you call "the quad" is four muscles in a group. Each exercise loaded different ones harder. The press hammered the outer territory. The extension hammered the front. Neither covered the full map.
That regional split appears wherever a muscle has more than one head. In the triceps, overhead extensions favored the long head while bench pressing favored the lateral head. In the calves, standing raises grew the deeper head with a probability above 99% compared to seated raises.
The reason is mechanical. A muscle crossing two joints partially shuts down during movements bending both joints at once. The front of the quad crosses the hip and the knee. During a leg press, both joints move simultaneously, and that muscle head contributes less. During an extension, only the knee moves, and the front quad fires fully. The exercise did not fail. It just could not reach every region equally.
The findings come from trained lifters using specific exercises, and whether identical splits hold for every muscle group is still an active research question. The regional principle, though, holds across every muscle tested: complete development of a multi-headed muscle requires exercises that load each head independently. Not because one exercise grows the muscle less, but because it grows certain parts of the muscle less.
The total-size question has an easy answer — any exercise works. The question of where that growth concentrates has a harder one, and it turns exercise selection from a counting problem into a mapping problem.
That reframes how many exercises you need entirely. The number was never the point. The coverage was.