More reps or more weight: which builds muscle?

Both. Adding reps grew muscle about as well as adding weight in an 8-week trial, so add reps first, then weight. Here is how Orion Coach does it.

By Orion Coach team·Published September 28, 2026·Last updated October 3, 2026

Add both, in order: reps first, then weight. A 2022 trial in trained lifters found that adding reps at the same load built about as much quad muscle as adding load, while adding load gave a little more squat strength. So neither lever is the "real" one, and a plan that uses both keeps you moving longer.

Should you add reps or weight to build muscle?

For muscle size, the evidence says it barely matters which one you push, as long as the sets are hard. For maximal strength, adding load has a small edge. Most lifters want both, which is why double progression (add reps until the top of a range, then add weight) is the default in good programs, and the rule Orion Coach runs. The full rule is in what double progression is.

The study

Plotkin and colleagues (2022, PeerJ) randomized 43 men and women aged 18 to 35, each with at least a year of lower-body training, into two groups for 8 weeks. Both did 4 sets each of back squat, leg extension and two calf raises, twice a week, with every set pushed to failure. One group added load each session. The other kept the load and added reps. Thirty-eight finished. The researchers measured muscle thickness by ultrasound at six thigh sites and three calf sites, plus Smith machine squat strength.

What they found

• Both groups grew. Across the six thigh sites, total quad thickness rose about 9.2% with added weight and 9.1% with added reps (our calculation from the paper's Table 1). The authors' adjusted analysis leaned slightly toward reps at the front of the thigh (rectus femoris, 2.8 mm, with an interval running from minus 0.5 to 5.8 mm).
• Squat 1RM rose a little more with added weight (about 21.8 kg vs 19.3 kg). Adjusted, the gap was 2.0 kg with an interval that included zero, which the authors describe as of questionable practical significance.

Why reps work: effort, not the number on the bar

A meta-analysis of sets taken to failure found similar muscle growth with light loads (60% of max or less) and heavy ones, while heavy loads built more 1RM strength (Schoenfeld et al., 2017). That is consistent with the usual explanation: as a set gets hard, your body recruits its high-threshold motor units at most loads. There is a floor, though. In a volume-matched trial, training at 20% of max grew the outer thigh (vastus lateralis) about 9% versus about 20% at 40, 60 and 80% of max, though only the gap with 80% was statistically clear (Lasevicius et al., 2018).

Coach Orion's call

I use both levers, in a fixed order: reps first, then weight. Your lift has a rep range and a target of about 2 reps in reserve. While your effort is on target, every set asks for one more rep next time at the same weight. Once your working sets average the top of the range, I add one weight step, 5 lb per hand on dumbbells, and reset you to the bottom.

That's the only way weight goes up. I never progress by a percentage, and a very easy session still earns one step, not two. I don't program sets to failure the way the study did. Going to failure is your choice, not my prescription. The full rule, including when weight comes down, is in double progression. More on how I progress you.

How fast the climb goes

Worked example: a walkthrough of how Orion applies this rule, not a real user's data.

• Dumbbell flat bench press in Orion Coach's 4-day Hypertrophy Intermediate program: 8 to 12 reps, about 2 reps in reserve, starting at 40 lb dumbbells for 10.
• In that program bench is on one day a week, so going from 10 reps to 12 and then up to 45 lb takes at least three weeks.
• On a program that trains a lift twice a week, the same climb takes half as long. Progress is counted per session of the lift, not per calendar week.

What the evidence doesn't tell us

The trial was 8 weeks, lower body only, in young trained adults, and every set went to failure. Orion leaves about 2 reps in reserve, so the effort is a little lower than the study's. Whether reps-first progression matches load progression over a year, or for upper-body lifts, hasn't been tested.

Watch the 20-second version on Instagram: @orioncoachapp.