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Quadriceps voluntary activation at different joint angles measured by two stimulation techniques
S A Newman1, G Jones, D J Newham
1Centre for Applied Biomedical Research, GKT School of Biomedical Sciences, Shepherd's House, King's College London, Guy's Campus, London, SE1 1UL, UK.
European Journal of Applied Physiology
|April 25, 2003
Summary
Quadriceps voluntary activation (VA) remains high across all knee angles during isometric contractions. Muscle length does not impact VA, and both nerve and muscle stimulation methods are effective for measurement.
Area of Science:
- Biomechanics
- Human Physiology
- Neuromuscular Function
Background:
- Quadriceps voluntary activation (VA) is fully achieved at mid-muscle length during brief isometric contractions.
- The influence of varying muscle lengths on quadriceps VA is not well-understood.
- The twitch superimposition technique is used to measure VA, with stimulation applied either intramuscularly or via the nerve trunk.
Purpose of the Study:
- To investigate quadriceps VA across a range of knee joint angles (10-110 degrees flexion).
- To compare VA measurements using magnetic nerve stimulation versus percutaneous electrical muscle stimulation.
- To determine if muscle length affects quadriceps VA during brief isometric contractions.
Main Methods:
- Eight healthy adults performed maximal voluntary quadriceps contractions at various knee joint angles.
- Voluntary activation (VA) was assessed using twitch superimposition via magnetic nerve stimulation and percutaneous electrical stimulation.
- Surface electromyography (EMG) of quadriceps and hamstrings was recorded.
Main Results:
- Nearly all subjects achieved >95% VA across all tested knee joint angles.
- Quadriceps VA did not significantly differ with changes in knee joint angle.
- No significant differences in VA were observed between the two stimulation techniques.
- Knee joint angle did not significantly affect quadriceps or hamstring EMG activity.
Conclusions:
- Quadriceps voluntary activation during brief isometric contractions is independent of muscle length.
- Both magnetic nerve stimulation and percutaneous electrical stimulation are reliable methods for assessing quadriceps VA.
- These findings support consistent neuromuscular control of the quadriceps across different joint positions.