Study analysis · International Journal of Sports Medicine · 2016
Switching up your weights doesn't make you stronger—here's what actually does.
Both mixing up heavy, medium, and light weights and sticking to just one weight range made guys stronger and bigger, with no clear winner.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study tried two different ways of lifting weights and saw if they made people stronger or bigger. It found both ways worked about the same, but it didn't prove one causes better results than the other — just that they both helped.
What’s the bottom line?
Two groups of guys lifted weights for 8 weeks — one used the same weight every time, the other switched between heavy, medium, and light weights.
How strong is this study?
The study did a good job by randomly assigning people to groups, which helps make things fair. But it only had 19 guys, and no one made sure they didn't know who was doing what — so we can't be totally sure the results aren't skewed by who tried harder or who measured the muscles.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
59 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=19)+1.8/20
- Follow-up+10/10
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 554 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
This design can establish causation. Randomization was confirmed, but blinding was unknown, which introduces potential performance and detection bias. However, since randomization was clearly stated and the study compared two interventions in a controlled setting, it can still support causal inference, albeit with moderate confidence.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding disclosures were reported in the study. All authors appear to be affiliated with academic institutions, and there is no indication of industry involvement.
The study lacks a formal conflict of interest statement or funding disclosure section, which is a limitation in transparency. However, author affiliations are all academic (universities and research institutes), and there is no evidence of industry ties, commercial sponsorship, or funder influence on study design or outcomes.
Key takeaways
- 01
Both groups got stronger and bigger.
- 02
The group that switched weights had slightly bigger gains in some areas, but not enough to say it was definitely better.
- 03
For trained lifters, you don’t need to stick to one rep range — mixing it up might help a little, but sticking to one range works just as well.
Surprising findings
- The group using light weights (20–30 RM) matched the gains of the moderate-rep group in muscle thickness.Most believe light weights only build endurance, not size—but this study shows they can drive hypertrophy just as well in trained individuals.
- Upper body endurance improved nearly 50% more in the varied group (effect size 1.91 vs. 1.28), despite no statistical significance.Endurance gains are usually tied to high-rep training—but here, mixing rep ranges outperformed constant training even in endurance, which was unexpected.
Practical takeaways
If you're bored with your routine, switch to varied rep ranges—your gains won't suffer, and you might get a small edge in endurance or arm size.
This only applies to trained lifters; beginners still benefit most from consistent progression in a moderate range.
medium confidenceDon't stress about hitting exactly 8–12 reps—lighter (20–30 RM) or heavier (2–4 RM) sets can still build muscle if you train close to failure.
Total volume and effort matter more than rep range—don't drop intensity just because you're using lighter weights.
medium confidenceWhy this study matters
Varied reps didn't beat constant reps—surprisingly
In an 8-week study with 19 trained men, the group using varied rep ranges (2–4, 8–12, and 20–30 RM) saw no statistically significant advantage over the group using only 8–12 RM for strength, muscle thickness, or endurance.
Most fitness gurus preach 'vary your rep ranges' as essential for growth—this study says for trained lifters, it might just be noise.
Effect sizes hinted at a hidden edge
Though not statistically significant, the varied group showed larger effect sizes: 0.80 vs. 0.57 for bench press strength, 1.91 vs. 1.28 for endurance, and up to 0.77 vs. 0.48 for elbow extensor thickness.
Even if the difference isn't 'proven,' the trend suggests varied loading might give you a subtle edge—worth testing if you're chasing every possible gain.
You don't need to stick to 8–12 reps to grow
Both groups improved muscle thickness significantly—even the 2–4 RM (heavy) and 20–30 RM (light) groups saw hypertrophy, proving muscle growth isn't locked to one rep range.
This shatters the myth that only moderate reps build muscle—light and heavy loads work too, as long as effort is high.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Two groups of guys lifted weights for 8 weeks — one used the same weight every time, the other switched between heavy, medium, and light weights.
Research results
Both groups got stronger and bigger. The group that switched weights had slightly bigger gains in some areas, but not enough to say it was definitely better.
What this means - more context
For trained lifters, you don’t need to stick to one rep range — mixing it up might help a little, but sticking to one range works just as well.
Compare effects of varied vs. constant loading zones on muscular adaptations in resistance-trained young men.
Both varied (2–4, 8–12, 20–30 RM) and constant (8–12 RM) training over 8 weeks significantly improved strength, muscle thickness, and endurance in trained men, with no statistically significant differences between groups, though effect sizes favored varied loading for several outcomes.
Methods Used
19 resistance-trained young men randomly assigned to either a varied-rep protocol (3 rep ranges across 3 days/week) or a constant-rep protocol (8–12 RM daily) for 8 weeks; outcomes measured included muscle thickness, maximal bench press strength, and local muscular endurance.
Main Finding
Both protocols produced significant gains in strength, hypertrophy, and endurance; no statistically significant differences between groups, but effect sizes favored varied loading for elbow flexor thickness (0.72 vs. 0.57), elbow extensor thickness (0.77 vs. 0.48), bench press strength (0.80 vs. 0.57), and upper body endurance (1.91 vs. 1.28).
Confidence Level
Moderate — randomized controlled trial with clear outcomes and reported effect sizes, but small sample size (n=19) and no confidence intervals reported.
Study Flags
Red Flags
- •Small sample size (n=19)
- •No confidence intervals reported
- •Short duration (8 weeks) limits long-term conclusions
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
The group using light weights (20–30 RM) matched the gains of the moderate-rep group in muscle thickness.
Most believe light weights only build endurance, not size—but this study shows they can drive hypertrophy just as well in trained individuals.
Practical Takeaways
If you're bored with your routine, switch to varied rep ranges—your gains won't suffer, and you might get a small edge in endurance or arm size.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 554 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Human RCT
Subject
Moderate probability
on the GRADE evidence scale
This study tried two different ways of lifting weights and saw if they made people stronger or bigger. It found both ways worked about the same, but it didn't prove one causes better results than the other — just that they both helped.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Randomized controlled trial design
- Clear intervention protocols
- Direct measurement of outcomes (muscle thickness, strength, endurance)
Weaknesses
- Blinding was unknown, risking performance and detection bias
- Very small sample size (n=19)
- No power analysis reported
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Two groups of guys lifted weights for 8 weeks — one used the same weight every time, the other switched between heavy, medium, and light weights.
Research results
Both groups got stronger and bigger. The group that switched weights had slightly bigger gains in some areas, but not enough to say it was definitely better.
What this means - more context
For trained lifters, you don’t need to stick to one rep range — mixing it up might help a little, but sticking to one range works just as well.
Compare effects of varied vs. constant loading zones on muscular adaptations in resistance-trained young men.
Both varied (2–4, 8–12, 20–30 RM) and constant (8–12 RM) training over 8 weeks significantly improved strength, muscle thickness, and endurance in trained men, with no statistically significant differences between groups, though effect sizes favored varied loading for several outcomes.
Methods Used
19 resistance-trained young men randomly assigned to either a varied-rep protocol (3 rep ranges across 3 days/week) or a constant-rep protocol (8–12 RM daily) for 8 weeks; outcomes measured included muscle thickness, maximal bench press strength, and local muscular endurance.
Main Finding
Both protocols produced significant gains in strength, hypertrophy, and endurance; no statistically significant differences between groups, but effect sizes favored varied loading for elbow flexor thickness (0.72 vs. 0.57), elbow extensor thickness (0.77 vs. 0.48), bench press strength (0.80 vs. 0.57), and upper body endurance (1.91 vs. 1.28).
Confidence Level
Moderate — randomized controlled trial with clear outcomes and reported effect sizes, but small sample size (n=19) and no confidence intervals reported.
Study Flags
Red Flags
- •Small sample size (n=19)
- •No confidence intervals reported
- •Short duration (8 weeks) limits long-term conclusions
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
The group using light weights (20–30 RM) matched the gains of the moderate-rep group in muscle thickness.
Most believe light weights only build endurance, not size—but this study shows they can drive hypertrophy just as well in trained individuals.
Practical Takeaways
If you're bored with your routine, switch to varied rep ranges—your gains won't suffer, and you might get a small edge in endurance or arm size.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 554 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Human RCT
Subject
Moderate probability
on the GRADE evidence scale
This study tried two different ways of lifting weights and saw if they made people stronger or bigger. It found both ways worked about the same, but it didn't prove one causes better results than the other — just that they both helped.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Randomized controlled trial design
- Clear intervention protocols
- Direct measurement of outcomes (muscle thickness, strength, endurance)
Weaknesses
- Blinding was unknown, risking performance and detection bias
- Very small sample size (n=19)
- No power analysis reported
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study did a good job by randomly assigning people to groups, which helps make things fair. But it only had 19 guys, and no one made sure they didn't know who was doing what — so we can't be totally sure the results aren't skewed by who tried harder or who measured the muscles.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
59 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=19)+1.8/20
- Follow-up+10/10
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 554 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
This design can establish causation. Randomization was confirmed, but blinding was unknown, which introduces potential performance and detection bias. However, since randomization was clearly stated and the study compared two interventions in a controlled setting, it can still support causal inference, albeit with moderate confidence.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding disclosures were reported in the study. All authors appear to be affiliated with academic institutions, and there is no indication of industry involvement.
The study lacks a formal conflict of interest statement or funding disclosure section, which is a limitation in transparency. However, author affiliations are all academic (universities and research institutes), and there is no evidence of industry ties, commercial sponsorship, or funder influence on study design or outcomes.
Standing
Who’s using this study?
The videos and claims on this site that lean on this study, and the researchers who wrote it.
1 video from House of Hypertrophy cite this study, drawing 0 claims from it.
No specific claims extracted from this video yet.
Authored by
6 researchersIf this is your work, this is how we attribute it on Fit Body Science. Brad Jon Schoenfeld is listed as the lead author.