How Hard Should Each Set Be?

Two questions decide how much a set is worth: how close to failure you take it, and how heavy the weight is. The research on both is reassuring, because it means you have a lot of flexibility as long as your effort is genuine.

How close to failure

You do not need to grind every set to absolute failure to grow. The evidence suggests that training within roughly one to three reps of failure captures most of the muscle building stimulus, while taking every set to failure adds a great deal of fatigue for a small extra return (Refalo et al., 2023).

A useful mental model is "reps in reserve" (RIR): if you could have done two more good reps when you stopped, that set was at 2 RIR. Keeping most working sets around 1 to 3 RIR lets you accumulate quality volume across a session without frying your recovery. Save true failure for the last set of isolation exercises, where the fatigue cost is lower.

Light weights vs heavy weights

For building muscle, load matters less than most lifters assume. A meta analysis by Schoenfeld and colleagues (2017) found that lighter and heavier loads produced similar muscle growth when sets were taken close to failure. In other words, effort, not the number on the plate, is what drives hypertrophy.

Heavier loads do have one clear advantage: they are better for building maximal strength, because strength is partly a skill of moving heavy weight. So use heavier loads and lower reps when strength is the goal, and feel free to use moderate or lighter loads for higher reps when the goal is size, both work.

Putting it together

Take most working sets to about 1 to 3 reps from failure, choose loads you can control through a full range of motion, and let your training log tell you when to add weight. That combination gives you the growth stimulus without the wreckage.