Even though barbell curls put more stress on the biceps when they’re stretched out, they don’t make your biceps grow bigger than cable curls — so stretching the muscle under load isn’t enough to guarantee more growth.
Scientific Claim
Training with barbell preacher curls does not produce greater biceps hypertrophy than cable preacher curls despite applying greater torque at longer muscle lengths, contradicting the hypothesis that mechanical tension at stretched positions preferentially drives muscle growth.
Original Statement
“The hypothesis that greater hypertrophy would be observed for the BAR group was not confirmed. The rationale was based on the greater internal physiological stress which would be produced by the muscle at a longer muscle length... which was not the case herein.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
definitive
Can make definitive causal claims
Assessment Explanation
The RCT was explicitly designed to test this hypothesis, with precise measurements and non-significant results (p=0.346), allowing definitive rejection of the hypothesis within the studied context.
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.
Systematic Review & Meta-AnalysisLevel 1aWhether training at longer muscle lengths consistently leads to greater hypertrophy across exercises and populations.
Whether training at longer muscle lengths consistently leads to greater hypertrophy across exercises and populations.
What This Would Prove
Whether training at longer muscle lengths consistently leads to greater hypertrophy across exercises and populations.
Ideal Study Design
A meta-analysis of RCTs comparing exercises with peak torque at long vs. short muscle lengths (e.g., deep vs. partial squats, full vs. partial curls), measuring muscle thickness via ultrasound or DXA, with standardized protocols and reporting of effect sizes.
Limitation: Cannot isolate mechanical tension from metabolic stress or volume differences.
Randomized Controlled TrialLevel 1bWhether mechanical tension at long lengths is necessary for hypertrophy, independent of volume and metabolic stress.
Whether mechanical tension at long lengths is necessary for hypertrophy, independent of volume and metabolic stress.
What This Would Prove
Whether mechanical tension at long lengths is necessary for hypertrophy, independent of volume and metabolic stress.
Ideal Study Design
A double-blind RCT with 100 young adults randomized to: 1) barbell preacher curls (long-length torque), 2) cable preacher curls (short-length torque), 3) isometric holds at long length, 4) isometric holds at short length — all matched for volume and time under tension, measuring biceps thickness pre/post 12 weeks.
Limitation: Cannot fully isolate tension from other stimuli; requires complex equipment and control.
Prospective Cohort StudyLevel 2bWhether long-length training leads to greater hypertrophy in trained individuals over time.
Whether long-length training leads to greater hypertrophy in trained individuals over time.
What This Would Prove
Whether long-length training leads to greater hypertrophy in trained individuals over time.
Ideal Study Design
A 3-year cohort tracking 200 resistance-trained adults who self-select long-length or short-length dominant exercises, measuring regional biceps hypertrophy via ultrasound annually.
Limitation: High risk of confounding from training history, diet, and recovery practices.
Evidence from Studies
Supporting (1)
Placing Greater Torque at Shorter or Longer Muscle Lengths? Effects of Cable vs. Barbell Preacher Curl Training on Muscular Strength and Hypertrophy in Young Adults
Both types of curls made people’s biceps grow about the same, even though one type stretched the muscle more. So stretching the muscle more doesn’t necessarily make it grow bigger.