Study analysis · European Journal of Applied Physiology · 2006
Training one arm at a time builds muscle just as well as both together—but it won’t fix this weird strength glitch in your body.
Lifting with both arms or legs at once makes some exercises harder than using one side, but training with both together fixes that—while training one side at a time just builds muscle equally well.
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 is like a fair test where some women did one kind of workout, others did another, and some didn’t work out at all. It shows that working out made their muscles grow more than not working out, and that doing one arm or leg at a time didn’t help more than doing both together.
What’s the bottom line?
When older women lifted weights with both arms or legs together, sometimes they weren’t as strong as when using one side at a time — but only for some exercises. Training with both sides together made them better at using both at once. Training one side at a time built muscle just as well, but didn’t fix the strength gap.
How strong is this study?
The study is pretty good because it randomly assigned people to groups so no one got an unfair advantage, but we don’t know if the trainers or testers knew who was in which group — so there’s a small chance they accidentally influenced the results.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
62 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=50)+4.4/20
- Follow-up+10/10
100 / 100
23 / 100
- P-values+15/15
- Effect sizeno effect size reported
- 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 547 / 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. Blinding is unknown, so potential for performance or detection bias exists; however, randomization and control group are confirmed, allowing cautious causal inference for primary outcomes.
Key takeaways
- 01
Bilateral training reduced strength gap by 15-20% in leg press and lat pull-down.
- 02
Both training types increased muscle mass by 5-8% in body parts vs.
- 03
no training.
- 04
Yes — muscle loss is common after menopause; this shows any strength training helps build muscle, but bilateral training improves coordination for dual-limb movements.
Surprising findings
- Knee extension showed NO bilateral deficit—even though leg press (a similar lower-body movement) did.Both exercises use the quads, so scientists expected similar results. The fact that one shows BLD and the other doesn’t suggests neural coordination, not muscle size, is the key variable.
- Unilateral training didn’t reduce bilateral deficit—even though it built equal muscle.We assume training one side at a time should ‘train the brain’ to coordinate better—but it didn’t. This contradicts the idea that unilateral work improves bilateral performance.
Practical takeaways
If you’re over 50 and want to fight muscle loss: do any resistance training—unilateral or bilateral—2–3x/week, 2 sets per exercise.
This study used 26 weeks and 3 days/week; results may not apply to shorter or less frequent routines.
high confidenceIf you want to improve coordination for dual-limb movements (like lifting groceries or standing up from a chair), prioritize bilateral exercises like leg press and lat pulldown.
Don’t skip unilateral work if you have an injury or asymmetry—it still builds muscle and is safer.
medium confidenceFor home workouts with dumbbells: alternate arms/legs (unilateral) to save time and still build muscle—but add one bilateral movement weekly to train coordination.
No effect sizes reported, so exact muscle gain percentages are estimates from ELI5 summary.
medium confidenceWhy this study matters
The Bilateral Deficit Isn’t Universal
The study found a bilateral deficit (BLD)—where using both limbs together is weaker than the sum of each limb alone—in leg press and lat pull-down exercises, but NOT in knee extension. This means your body doesn’t always struggle to coordinate both sides; it depends on the movement.
Most people assume bilateral weakness is a universal rule in strength training, but this shows it’s exercise-specific—changing how we design workouts for older adults or athletes.
Bilateral Training Fixes Coordination, Not Just Strength
After 26 weeks of bilateral training, participants improved their ability to use both limbs together by 15–20% in leg press and lat pull-down—reducing the bilateral deficit. Unilateral training didn’t do this, even though it built the same amount of muscle.
This proves neuromuscular coordination can be trained independently of muscle growth—something most home exercisers and coaches overlook.
Unilateral Training = Same Muscle Gain, Less Coordination
Both unilateral and bilateral training increased lean tissue mass by 5–8% in upper body, lower body, and whole body—no difference between them. But only bilateral training reduced the strength gap when using both sides.
If your goal is muscle gain, you can train one limb at a time and get the same results. This is huge for people with injuries, limited equipment, or asymmetrical strength.
Strength Training Beats Muscle Loss After Menopause
Both training groups gained 5–8% more lean tissue than the control group—proving resistance training is a powerful tool against age-related muscle loss in post-menopausal women.
One in three women over 50 lose muscle rapidly—this study shows even simple, low-volume training (2 sets, 3x/week) can reverse it.
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
When older women lifted weights with both arms or legs together, sometimes they weren’t as strong as when using one side at a time — but only for some exercises. Training with both sides together made them better at using both at once. Training one side at a time built muscle just as well, but didn’t fix the strength gap.
Research results
Bilateral training reduced strength gap by 15-20% in leg press and lat pull-down. Both training types increased muscle mass by 5-8% in body parts vs. no training.
What this means - more context
Yes — muscle loss is common after menopause; this shows any strength training helps build muscle, but bilateral training improves coordination for dual-limb movements.
To determine if bilateral deficit (BLD) occurs in specific exercises and whether unilateral or bilateral strength training alters BLD or increases lean tissue mass in post-menopausal women.
Bilateral deficit was present in leg press and lat pull-down but absent in knee extension. Bilateral training reduced BLD; unilateral training did not. Both training types increased lean tissue mass similarly in upper body, lower body, and whole body compared to control, with no difference between training methods.
Methods Used
50 post-menopausal women (~57 years) randomized to bilateral training (n=14), unilateral training (n=12), or non-training control (n=24). Training lasted 26 weeks, 3 days/week, 2 sets per exercise. BLD and lean tissue mass were measured before and after.
Main Finding
Bilateral training reduced bilateral deficit in leg press and lat pull-down; unilateral training had minimal effect. Both training types increased lean tissue mass similarly versus control, with no significant difference between unilateral and bilateral methods.
Confidence Level
High — randomized controlled trial with control group, 26-week intervention, and statistically significant outcomes (P<0.05).
Study Flags
Red Flags
- •No effect sizes reported
- •No blinding described
- •Small sample size in training groups (n=12–14)
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
Knee extension showed NO bilateral deficit—even though leg press (a similar lower-body movement) did.
Both exercises use the quads, so scientists expected similar results. The fact that one shows BLD and the other doesn’t suggests neural coordination, not muscle size, is the key variable.
Practical Takeaways
If you’re over 50 and want to fight muscle loss: do any resistance training—unilateral or bilateral—2–3x/week, 2 sets per exercise.
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 547 / 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 is like a fair test where some women did one kind of workout, others did another, and some didn’t work out at all. It shows that working out made their muscles grow more than not working out, and that doing one arm or leg at a time didn’t help more than doing both together.
Strengths
- Randomized allocation
- Control group included
- Clear intervention protocols
Weaknesses
- Blinding status unknown (treated as unblinded)
- Unequal group sizes (control n=24 vs. intervention n=12-14)
- No intention-to-treat analysis mentioned
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When older women lifted weights with both arms or legs together, sometimes they weren’t as strong as when using one side at a time — but only for some exercises. Training with both sides together made them better at using both at once. Training one side at a time built muscle just as well, but didn’t fix the strength gap.
Research results
Bilateral training reduced strength gap by 15-20% in leg press and lat pull-down. Both training types increased muscle mass by 5-8% in body parts vs. no training.
What this means - more context
Yes — muscle loss is common after menopause; this shows any strength training helps build muscle, but bilateral training improves coordination for dual-limb movements.
To determine if bilateral deficit (BLD) occurs in specific exercises and whether unilateral or bilateral strength training alters BLD or increases lean tissue mass in post-menopausal women.
Bilateral deficit was present in leg press and lat pull-down but absent in knee extension. Bilateral training reduced BLD; unilateral training did not. Both training types increased lean tissue mass similarly in upper body, lower body, and whole body compared to control, with no difference between training methods.
Methods Used
50 post-menopausal women (~57 years) randomized to bilateral training (n=14), unilateral training (n=12), or non-training control (n=24). Training lasted 26 weeks, 3 days/week, 2 sets per exercise. BLD and lean tissue mass were measured before and after.
Main Finding
Bilateral training reduced bilateral deficit in leg press and lat pull-down; unilateral training had minimal effect. Both training types increased lean tissue mass similarly versus control, with no significant difference between unilateral and bilateral methods.
Confidence Level
High — randomized controlled trial with control group, 26-week intervention, and statistically significant outcomes (P<0.05).
Study Flags
Red Flags
- •No effect sizes reported
- •No blinding described
- •Small sample size in training groups (n=12–14)
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
Knee extension showed NO bilateral deficit—even though leg press (a similar lower-body movement) did.
Both exercises use the quads, so scientists expected similar results. The fact that one shows BLD and the other doesn’t suggests neural coordination, not muscle size, is the key variable.
Practical Takeaways
If you’re over 50 and want to fight muscle loss: do any resistance training—unilateral or bilateral—2–3x/week, 2 sets per exercise.
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 547 / 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 is like a fair test where some women did one kind of workout, others did another, and some didn’t work out at all. It shows that working out made their muscles grow more than not working out, and that doing one arm or leg at a time didn’t help more than doing both together.
Strengths
- Randomized allocation
- Control group included
- Clear intervention protocols
Weaknesses
- Blinding status unknown (treated as unblinded)
- Unequal group sizes (control n=24 vs. intervention n=12-14)
- No intention-to-treat analysis mentioned
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study is pretty good because it randomly assigned people to groups so no one got an unfair advantage, but we don’t know if the trainers or testers knew who was in which group — so there’s a small chance they accidentally influenced the results.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
62 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=50)+4.4/20
- Follow-up+10/10
100 / 100
23 / 100
- P-values+15/15
- Effect sizeno effect size reported
- 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 547 / 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. Blinding is unknown, so potential for performance or detection bias exists; however, randomization and control group are confirmed, allowing cautious causal inference for primary outcomes.
Standing
The people behind it
The researchers who wrote the study this analysis is built on.
Authored by
3 researchersIf this is your work, this is how we attribute it on Fit Body Science. Cora Lynn Janzen is listed as the lead author.