Whether you do full or half curls, the upper part of your bicep grows about the same amount—so where you curl doesn’t matter much for that part of the muscle.
Scientific Claim
In resistance-trained individuals, both partial range of motion training at long muscle lengths (0°–70°) and full range of motion training (0°–140°) induce similar and significant hypertrophy in the proximal elbow flexors (at 50% humeral length), with trivial effect size (SMD = 0.04) and weak Bayesian evidence (BF = 2.66), indicating that regional hypertrophy is not uniformly enhanced by ROM manipulation.
Original Statement
“Results showed similar improvements in muscle thickness at 50% humeral length between conditions, whereas pROMinitial exhibited trivial to small superiority at 70% elbow flexor length (standardized mean difference [SMD] = 0.10 and Bayes factor = 4.87).”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
probability
Can suggest probability/likelihood
Assessment Explanation
The trivial effect size and weak Bayes factor justify neutral language. The claim correctly avoids implying superiority and reflects the data’s lack of meaningful difference.
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 ROM manipulation (pROMinitial vs. fROM) has no differential effect on proximal muscle hypertrophy across multiple studies in trained populations.
Whether ROM manipulation (pROMinitial vs. fROM) has no differential effect on proximal muscle hypertrophy across multiple studies in trained populations.
What This Would Prove
Whether ROM manipulation (pROMinitial vs. fROM) has no differential effect on proximal muscle hypertrophy across multiple studies in trained populations.
Ideal Study Design
A meta-analysis of all RCTs comparing pROMinitial and fROM in resistance-trained adults, measuring muscle thickness at 50% humeral length, with standardized ultrasound protocols and sufficient sample sizes per study (n≥20).
Limitation: Cannot determine if differences exist in other muscle groups or under different training volumes.
Randomized Controlled TrialLevel 1bIn EvidenceWhether pROMinitial and fROM produce equivalent proximal elbow flexor hypertrophy in trained individuals.
Whether pROMinitial and fROM produce equivalent proximal elbow flexor hypertrophy in trained individuals.
What This Would Prove
Whether pROMinitial and fROM produce equivalent proximal elbow flexor hypertrophy in trained individuals.
Ideal Study Design
A double-blind, randomized, crossover RCT with 80+ resistance-trained adults, performing 12 weeks of unilateral preacher curls (pROMinitial vs. fROM), with pre/post ultrasound measurements of muscle thickness at 50% humeral length, controlling for volume and intensity.
Limitation: Still limited to one muscle group and one exercise.
Prospective Cohort StudyLevel 2bWhether habitual use of pROMinitial or fROM leads to similar proximal muscle growth over time in real-world training.
Whether habitual use of pROMinitial or fROM leads to similar proximal muscle growth over time in real-world training.
What This Would Prove
Whether habitual use of pROMinitial or fROM leads to similar proximal muscle growth over time in real-world training.
Ideal Study Design
A 2-year prospective cohort of 300+ resistance-trained lifters self-selecting pROMinitial or fROM training, with quarterly ultrasound measurements of muscle thickness at 50% humeral length, controlling for training history and nutrition.
Limitation: Subject to confounding variables and self-reporting bias.
Animal Model StudyLevel 4Whether mechanical tension at different joint angles affects proximal vs. distal muscle fiber growth in a controlled setting.
Whether mechanical tension at different joint angles affects proximal vs. distal muscle fiber growth in a controlled setting.
What This Would Prove
Whether mechanical tension at different joint angles affects proximal vs. distal muscle fiber growth in a controlled setting.
Ideal Study Design
A rat study with 40 animals, trained for 8 weeks with either pROMinitial or fROM elbow flexion, measuring fiber CSA and sarcomere number in proximal and distal regions of the biceps brachii via histology.
Limitation: Cannot replicate human training motivation or neural adaptation.
Cross-Sectional StudyLevel 3Whether experienced lifters using pROMinitial have similar proximal muscle thickness as those using fROM.
Whether experienced lifters using pROMinitial have similar proximal muscle thickness as those using fROM.
What This Would Prove
Whether experienced lifters using pROMinitial have similar proximal muscle thickness as those using fROM.
Ideal Study Design
A cross-sectional study comparing muscle thickness at 50% humeral length in 100+ trained lifters who primarily use pROMinitial vs. fROM, matched for training age, volume, and sex.
Limitation: Cannot determine causality or direction of effect.
Evidence from Studies
Supporting (1)
Both partial and full arm curls made the upper part of the biceps grow about the same amount, so doing partial curls isn’t worse than full curls for building that part of the muscle.