When you train one muscle at a time (like leg extensions), you get a bit better at holding still with that muscle—more than if you train big compound moves like squats. But either way, you get way stronger at moving than holding.
Scientific Claim
Single-joint resistance training produces greater transfer of strength gains to isometric contractions than multi-joint training, but both show significantly larger improvements in dynamic strength than isometric strength.
Original Statement
“The transferability of muscle strength demonstrated a moderate effect (SMD = 0.70) for single-joint exercises and a small effect for the multi-joint exercises (SMD = 0.33), whereas the task specificity was moderate to large (SMD = 1.02 and 1.30) for the multi-joint and single-joint exercises.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The study reports SMDs with confidence intervals and uses appropriate language ('demonstrated a moderate effect'). No causal claims are made, and the subgroup analysis is justified.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.
Randomized Controlled TrialLevel 1bWhether single-joint RT causes greater isometric strength transfer than multi-joint RT when matched for volume and intensity.
Whether single-joint RT causes greater isometric strength transfer than multi-joint RT when matched for volume and intensity.
What This Would Prove
Whether single-joint RT causes greater isometric strength transfer than multi-joint RT when matched for volume and intensity.
Ideal Study Design
A 10-week RCT with 120 healthy adults randomized to: (1) single-joint knee extension RT, (2) multi-joint squat RT, (3) control. All groups matched for volume (sets × reps × load). Primary outcomes: change in isometric knee extension torque and 1RM knee extension.
Limitation: Cannot determine if results generalize to upper body or other muscle groups.
Cross-Sectional StudyLevel 3Whether habitual users of single-joint vs. multi-joint RT show different ratios of isometric to dynamic strength.
Whether habitual users of single-joint vs. multi-joint RT show different ratios of isometric to dynamic strength.
What This Would Prove
Whether habitual users of single-joint vs. multi-joint RT show different ratios of isometric to dynamic strength.
Ideal Study Design
A cross-sectional study of 200 resistance-trained adults categorized by primary training modality (single-joint dominant vs. multi-joint dominant), measuring 1RM and isometric MVC for target muscles and calculating the isometric/dynamic strength ratio.
Limitation: Cannot determine if differences are due to training type or selection bias (e.g., rehab patients prefer single-joint).
Evidence from Studies
Supporting (0)
Contradicting (1)
Task Specificity of Dynamic Resistance Training and Its Transferability to Non-trained Isometric Muscle Strength: A Systematic Review with Meta-analysis
The study found that lifting weights in dynamic movements makes you much stronger in those movements, but only slightly stronger in holding still (isometric) tests — which matches part of the claim. But it didn’t compare single-joint vs. multi-joint exercises to see if one transfers better to holding still, so we can’t say single-joint is better.