Growth is similar across a wide rep range
Research comparing light and heavy loads has repeatedly shown that muscle growth is comparable across a broad span of repetitions, roughly five to thirty per set, provided each set is taken close to muscular failure. Whether someone lifts a heavy weight for five hard reps or a lighter weight for twenty-five hard reps, the hypertrophy stimulus ends up similar when effort is matched. The body appears to respond to high-effort tension across the loading spectrum rather than to one magic rep count.
The important qualifier is proximity to failure. Light loads only match heavy loads for growth when the set is genuinely difficult and the final reps are close to the limit.
Where heavier and lighter loads still differ
Although growth is similar, the trade-offs are not. Heavier loads in lower rep ranges develop maximal strength more efficiently and involve less time under tension per set. Lighter loads at high reps build more local discomfort and can be very fatiguing as the set drags on, but spare the joints from peak loads.
These are general patterns from training research, not individualized prescriptions. Load selection should account for experience, joint health, and goals, and is best guided by a qualified coach. This is educational information, not medical advice.