Heavy weights win for strength, but any load builds muscle

Anyone who lifts weights faces the same three decisions: how heavy, how many sets and how often each week. Advice on these variables is famously contradictory, with some camps insisting heavy loads are essential and others arguing lighter work does just as much. Individual trials are usually too small to compare more than two approaches at once. This review set out to compare twelve distinct training prescriptions against each other and against doing nothing, to see which combinations actually maximise strength and muscle growth in healthy adults.

Researchers searched six databases up to February 2022 for randomised trials in healthy adults that compared at least two predefined conditions, differentiated by load, sets and weekly frequency, or a non-exercise control. They used a Bayesian network meta-analysis, a technique that lets every prescription be compared with every other even when no trial tested them head to head. The strength analysis drew on 178 studies with 5097 participants, 45% of them women. The muscle growth analysis included 119 studies with 3364 participants, 47% women, and the robustness of the rankings was checked with threshold analysis.

Every training prescription beat no exercise for both strength and muscle size. For strength, prescriptions using loads above 80% of one repetition maximum ranked highest, and the single top-ranked recipe was higher load, multiple sets, three times a week. For muscle growth, all prescriptions performed comparably, with higher load, multiple sets, twice a week ranked first. Many prescriptions produced similar calculated effects, and the threshold analysis showed the overall rankings were extremely robust.

This is one of the largest attempts yet to rank training prescriptions rather than simply compare lifting with not lifting. It supports the long-standing view that heavier loads are the most efficient route to strength, while extending the evidence that muscle size responds to a wide range of loads. It also suggests the differences between sensible programmes are smaller than gym folklore implies. What it cannot settle is how these averages play out for a specific individual, or how prescriptions interact with years of training experience.

The encouraging message is that there is no single magic programme: essentially any structured resistance training builds strength and muscle compared with doing nothing. If strength is the priority, this is a reason to think heavier loads, above 80% of one repetition maximum, are the more efficient choice. If muscle size is the goal, the load appears to matter far less than accumulating multiple sets. Showing up consistently looks more important than perfecting any one variable.