If you do hamstring holds with your knee almost fully bent, you might get stronger at that angle more than if you do the same exercise with your knee only slightly bent—even if you're pushing with the same total force.
Scientific Claim
Low-intensity isometric training at short muscle length (90° knee flexion) may lead to greater improvements in hamstring strength at that joint angle compared to training at long muscle length (30° knee flexion), despite similar total torque during training.
Original Statement
“As for MVC at 90° knee flexion, there was a significant time × group interaction (p < 0.05) and a significant simple main effect of time in both the LL (p < 0.01; Cohen's d effect size [ES] = 0.36) and SL (p < 0.01; ES = 0.64) training groups.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
probability
Can suggest probability/likelihood
Assessment Explanation
The RCT design supports causal inference, but lack of blinding and unknown measurement bias limits confidence. 'May lead to' appropriately reflects low-confidence causality under GRADE.
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 short muscle length consistently produces greater angle-specific strength gains than long-length training across multiple studies.
Whether training at short muscle length consistently produces greater angle-specific strength gains than long-length training across multiple studies.
What This Would Prove
Whether training at short muscle length consistently produces greater angle-specific strength gains than long-length training across multiple studies.
Ideal Study Design
A meta-analysis of 12+ RCTs comparing isometric training at short vs. long muscle lengths (e.g., 90° vs. 30° knee flexion) in healthy young adults, using standardized protocols (30–40% MVC, 3x/week, 6–12 weeks), with MVC at trained angle as primary outcome and effect size pooling.
Limitation: Cannot determine if differences are due to neural adaptation, muscle architecture, or measurement artifacts.
Randomized Controlled TrialLevel 1bIn EvidenceCausal effect of training at short vs. long muscle length on angle-specific strength gains.
Causal effect of training at short vs. long muscle length on angle-specific strength gains.
What This Would Prove
Causal effect of training at short vs. long muscle length on angle-specific strength gains.
Ideal Study Design
A double-blind, crossover RCT of 40 young adults randomized to two 8-week phases: 90° vs. 30° isometric hamstring training (30% MVC, 3x/week), with washout period, and primary outcome: MVC at 90° and 30° measured by isokinetic dynamometer with blinded assessors.
Limitation: Crossover design may be limited by carryover effects or learning effects in strength testing.
Prospective Cohort StudyLevel 2bWhether the strength advantage from short-length training persists over time after training ends.
Whether the strength advantage from short-length training persists over time after training ends.
What This Would Prove
Whether the strength advantage from short-length training persists over time after training ends.
Ideal Study Design
A 12-month prospective cohort of 80 young adults completing 8 weeks of either SL or LL isometric training, with MVC measurements at 0, 3, 6, and 12 months to assess retention of angle-specific gains.
Limitation: Cannot control for concurrent training or lifestyle changes.
Case-Control StudyLevel 3bWhether individuals with prior hamstring injuries show different strength gains from SL vs. LL training.
Whether individuals with prior hamstring injuries show different strength gains from SL vs. LL training.
What This Would Prove
Whether individuals with prior hamstring injuries show different strength gains from SL vs. LL training.
Ideal Study Design
A case-control study comparing 30 athletes with prior hamstring strains to 30 healthy controls, both undergoing identical SL and LL training protocols, measuring MVC at 90° and 30° pre- and post-intervention.
Limitation: Cannot establish causation due to non-randomized group assignment.
Evidence from Studies
Supporting (1)
People who trained with their knee bent at 90° got stronger at that angle more than people who trained with their knee bent at 30°, even though both groups pushed with the same total force. So bending your knee more while training helps you get stronger in that position.