Even though people push with the same total force during hamstring holds whether their knee is bent or straight, their muscles are actually working less hard when the knee is more bent.
Scientific Claim
Total torque during low-intensity isometric hamstring training is similar between training at long and short muscle lengths, but active torque (muscle-generated force) is significantly lower at long muscle lengths.
Original Statement
“The active torque because of muscle contraction was calculated by subtracting the passive torque at rest from the total torque (30% MVC). The active torque was significantly lower in the LL training group than in the SL training group (p < 0.01), whereas there was no between-group difference in total torque during training.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
definitive
Can make definitive causal claims
Assessment Explanation
This is a direct measurement comparison reported with statistical significance (p<0.01). The claim describes an observed difference, not a causal effect, so definitive language is appropriate.
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 1bIn EvidenceWhether the difference in active torque between long and short muscle lengths is consistent across individuals and measurement systems.
Whether the difference in active torque between long and short muscle lengths is consistent across individuals and measurement systems.
What This Would Prove
Whether the difference in active torque between long and short muscle lengths is consistent across individuals and measurement systems.
Ideal Study Design
A within-subject RCT of 30 young adults performing isometric hamstring contractions at 30° and 90° knee flexion, with active torque measured via force plate and EMG-controlled MVC, repeated across three sessions to assess reliability.
Limitation: Does not establish whether this torque difference causes adaptation differences.
Cross-Sectional StudyLevel 3aWhether active torque differences at long vs. short lengths are consistent across age groups or muscle fiber types.
Whether active torque differences at long vs. short lengths are consistent across age groups or muscle fiber types.
What This Would Prove
Whether active torque differences at long vs. short lengths are consistent across age groups or muscle fiber types.
Ideal Study Design
A cross-sectional study comparing active torque production at 30° and 90° knee flexion during 30% MVC isometric contractions in 100 healthy adults aged 18–65, using MRI to assess muscle architecture and EMG to normalize activation.
Limitation: Cannot determine causality or training-induced changes.
Animal StudyLevel 4Whether passive tissue contributions to total torque differ by muscle length in isolated muscle preparations.
Whether passive tissue contributions to total torque differ by muscle length in isolated muscle preparations.
What This Would Prove
Whether passive tissue contributions to total torque differ by muscle length in isolated muscle preparations.
Ideal Study Design
An in vivo rat study measuring passive and active torque in the hamstring complex during isometric contractions at 30° and 90° knee flexion, with direct muscle stimulation and force transducer measurements.
Limitation: Cannot be directly extrapolated to humans due to anatomical and neural differences.
Evidence from Studies
Supporting (1)
The study found that when people did gentle hamstring exercises with their knee bent a little (long muscle) vs. a lot (short muscle), the total force they felt was the same — but their muscles had to work harder to produce that force when the muscle was stretched out. So yes, muscles make less force when stretched, even if the total effort feels the same.