Most of the studies on this topic are not very well done—they often don’t report enough details, have small sample sizes, or use shaky methods, so we can’t trust their results fully.
Scientific Claim
The methodological quality of existing studies comparing longer- and shorter-muscle-length resistance training is generally poor or fair, with no study achieving high methodological rigor according to the SMART-LD scale.
Original Statement
“The SMART-LD scale was used to assess the quality of all studies included. A mean score of (11.4 ± 1.9) out of 20 points (range: 9 to 14 points). Four studies were deemed of poor quality, and the remaining four studies were deemed of fair quality. No studies were deemed to be of good quality.”
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 claim directly reports the authors’ own quality assessment using a validated scale (SMART-LD), with exact scores and distribution. No overstatement is present.
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 1aPooled effect of high-quality RCTs on LML-RT outcomes, excluding low-quality studies.
Pooled effect of high-quality RCTs on LML-RT outcomes, excluding low-quality studies.
What This Would Prove
Pooled effect of high-quality RCTs on LML-RT outcomes, excluding low-quality studies.
Ideal Study Design
A meta-analysis of only high-quality RCTs (SMART-LD ≥16) comparing LML-RT and SML-RT, with standardized protocols, adequate blinding, and MRI-based hypertrophy outcomes, to determine if conclusions change when low-quality studies are excluded.
Limitation: May have insufficient studies to perform meaningful analysis.
Randomized Controlled TrialLevel 1bEffect of LML-RT under high methodological rigor.
Effect of LML-RT under high methodological rigor.
What This Would Prove
Effect of LML-RT under high methodological rigor.
Ideal Study Design
A double-blind, placebo-controlled RCT with 100 untrained adults, randomized to LML-RT or SML-RT, with standardized training logs, blinded outcome assessors, MRI for muscle volume, extended-field-of-view ultrasound for fascicle length, and pre-registered analysis plan.
Limitation: High cost and complexity limit replication.
Prospective Cohort StudyLevel 2aReal-world effectiveness of LML-RT under rigorous monitoring.
Real-world effectiveness of LML-RT under rigorous monitoring.
What This Would Prove
Real-world effectiveness of LML-RT under rigorous monitoring.
Ideal Study Design
A 1-year prospective cohort of 200 adults with daily training logs, weekly ultrasound assessments, and biometric monitoring, comparing LML-RT and SML-RT groups with strict adherence criteria.
Limitation: Cannot control for all lifestyle confounders.
Cross-Sectional StudyLevel 3Association between training quality and outcomes in real-world populations.
Association between training quality and outcomes in real-world populations.
What This Would Prove
Association between training quality and outcomes in real-world populations.
Ideal Study Design
A cross-sectional survey of 500 resistance-trained individuals with detailed training logs and ultrasound measurements, correlating adherence to SMART-LD criteria with hypertrophy outcomes.
Limitation: Self-reported data introduces bias; cannot infer causation.
In Vitro Cell StudyLevel 5Molecular basis for why poor methodology affects outcomes.
Molecular basis for why poor methodology affects outcomes.
What This Would Prove
Molecular basis for why poor methodology affects outcomes.
Ideal Study Design
In vitro study comparing gene expression responses to mechanical stretch under controlled vs. uncontrolled conditions to model how poor study design distorts biological signals.
Limitation: Does not reflect whole-body human physiology.
Evidence from Studies
Supporting (1)
Does longer-muscle length resistance training cause greater longitudinal growth in humans? A systematic review
This study looked at other research on different ways to do weight training and found that most of those studies used shaky methods, so we can’t be very sure of their results — which matches the claim that the science here isn’t very strong.