REF-1480 · Chaves et al., 2024 · International Journal of Sports Medicine · Paper · PubMed

Does it matter if I add weight or reps?

In 39 untrained adults over 10 weeks, legs progressed by either gained leg-extension 1RM and thigh size with no significant difference; equivalence not shown. Abstract only; no increment rule.

Main caveat: Abstract only. The training exercise, progression rule, sets, reps, effort, adherence, blinding and the size of any between-leg difference with its interval…
moderate evidenceMeasured on non-athletes and recreational people

Chaves and colleagues asked whether progressing resistance training by load (LOADprog) or by reps (REPSprog) changes strength and muscle size. They used a within-subject design: 39 previously untrained young people had their legs randomised to the two protocols, and trained for 10 weeks.

Leg-extension 1RM rose in both, from 52.90 ± 16.32 to 69.05 ± 18.55 kg with load and from 51.67 ± 15.84 to 66.82 ± 17.95 kg with reps. Vastus lateralis cross-sectional area by ultrasound rose from 21.34 ± 4.71 to 23.53 ± 5.41 cm² and from 21.08 ± 4.62 to 23.39 ± 5.19 cm².

The abstract reports no difference between protocols (P > 0.05) and concludes either can be used in the early stages of training. Our reading: with the same people as their own controls this is a useful second trial alongside REF-1479, in the other population. A non-significant P is not proof they are the same, and the abstract gives no interval for the difference.

It does not state the increment rule the guide wants; that is not available from the abstract.

Protocol

Design: within-subject; each participant's legs randomised to LOADprog or REPSprog; assessed before and after 10 weeks.
Who: n = 39 previously untrained young persons: 20 men, 19 women.
Increment rule: not given in the abstract. The training exercise, starting load, rep targets, sets, weekly frequency, effort and how much was added are not stated. The publisher's copy could not be fetched.
Outcomes: leg-extension 1RM; vastus lateralis cross-sectional area by ultrasonography.
Funding and interests: "The authors declare that they have no conflict of interest." Funding is not in the abstract; Crossref and Europe PMC list FAPESP and CNPq (Brazilian public research funders).

Key Results

OutcomeProtocolPrePostChange (our arithmetic)
Leg-extension 1RM (kg)LOADprog52.90 ± 16.3269.05 ± 18.55+16.15
Leg-extension 1RM (kg)REPSprog51.67 ± 15.8466.82 ± 17.95+15.15
Vastus lateralis CSA (cm²)LOADprog21.34 ± 4.7123.53 ± 5.41+2.19
Vastus lateralis CSA (cm²)REPSprog21.08 ± 4.6223.39 ± 5.19+2.31
Between protocols: reported only as no difference, P > 0.05, for both outcomes. No effect size or confidence interval for the difference in the abstract.

Mechanisms

Measured: 1RM and muscle area only; no neural or fibre data in the abstract.
Authors' interpretation: either approach can be used to promote gains in young people in the early stages of training.
Inference: in beginners much early strength gain is commonly attributed to neural learning (PHYS-20), and training at different rep numbers still improves it. Not tested here. Training one leg may also influence the other in a within-subject design (REF-1476 lists cross-education); this could narrow a true gap.

Practical Application

Does it matter if I add weight or reps? In 39 untrained adults over 10 weeks, legs progressed by either gained leg-extension 1RM and thigh size with no significant difference; equivalence not shown. Abstract only; no increment rule.
For a beginner: pick whichever the gym and log allow (inference; the abstract does not name the trained exercise). No rule comes from this paper, and "the same" isn't shown.
Not from this paper; the base's own practice: one axis at a time, and a heavy-strength phase later for those who need it (SYNTH-43, SYNTH-44).
Does not extend to: trained lifters (REF-1479 covers those, with its own limits), heavy barbell work, bodyweight moves, carries or stations.

Limitations

Abstract only. The training exercise, progression rule, sets, reps, effort, adherence, blinding and the size of any between-leg difference with its interval were not available.
A null, not equivalence. No equivalence test is in the abstract; the point changes are close, and the interval is unknown.
One test, one muscle. 1RM on leg extension and the size of one muscle; the abstract does not say whether the exercise tested was the one trained.
Within-subject design. Each leg is its own control, which helps power; effects spilling between legs can't be ruled out from the abstract.
Who. Untrained young men and women; not endurance athletes; no training-status transfer.
How this entry was checked and changed
Why this level

rubric's controlled crossover-type comparison with ≥15, each person their own control; randomised limbs, n = 39. Untrained people, and an abstract that omits the training exercise, the increment rule, adherence and any interval