Each extra weekly set adds less

Four syntheses (Ralston 2017, Androulakis-Korakakis 2020, Currier 2023 and Pelland 2026) show that more sets give somewhat more strength, with strongly diminishing returns.

In the Schoenfeld 2019 randomised trial, 34 trained men did 1, 3 or 5 sets per exercise three times a week for eight weeks. Strength rose alike in all groups, while muscle size rose with volume.

For strength, a small number of hard sets already gives most of the gain. When you add sets, expect a smaller gain from each one.

The figure of roughly 10 to 20 sets per muscle per week, past which extra sets add little, comes from practice, not research. The research confirms diminishing returns, not an exact cut-off.