When total training volume is held constant, muscle hypertrophy is equivalent between low-load resistance training (8–12 repetitions per set) and high-load resistance training (3–5 repetitions per set).

Study: Muscle Hypertrophy, Strength, and Salivary Hormone Changes Following 9 Weeks of High- or Low-Load Resistance Training

People who lifted light weights for more reps grew their muscles just as much as those who lifted heavy weights for fewer reps—as long as they did the same total amount of work. So, whether you go light or heavy, your muscles grow similarly if you push to fatigue the same number of times.

Study: Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men

The study found that whether people lifted light weights for many reps or heavy weights for fewer reps — as long as they worked until exhaustion and did the same total amount of work — their muscles grew the same amount. This supports the idea that how heavy the weight is doesn’t matter as much as how much you do overall.

Study: Effects of rest intervals and training loads on metabolic stress and muscle hypertrophy

The study found that lifting lighter weights with more reps and less rest built muscle just as well—and even better—than lifting heavy weights with fewer reps, as long as the total work done was the same.

Study: Muscle hypertrophy and strength gains after resistance training with different volume matched loads: a systematic review and meta-analysis.

When people lift light weights for more reps or heavy weights for fewer reps but do the same total amount of work, their muscles grow just as much either way — and this study proves it.