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In vivo load sharing among the quadriceps components.
Li-Qun Zhang1, Guangzhi Wang, Gordon W Nuber
1Department of Orthopaedic Surgery, Northwestern University, 645 N. Michigan Avenue, Suite 910, Chicago, IL 60611-4496, USA. l-zhang@northwestern.edu
Summary
The vastus intermedius muscle contributes most to knee extension force, with its relative role decreasing as force increases. The central nervous system favors this muscle during lower activation levels.
Area of Science:
- Biomechanics
- Human Physiology
- Musculoskeletal Research
Background:
- Knee extension involves coordinated quadriceps muscle contractions.
- Load distribution among quadriceps components during knee extension is not fully understood.
- Investigating muscle contribution is crucial for understanding normal and pathological knee function.
Purpose of the Study:
- To determine how load is shared among quadriceps components during knee extension.
- To investigate the relationship between muscle activation and force contribution.
- To understand the central nervous system's strategy in utilizing quadriceps muscles.
Main Methods:
- Used electrical stimulation for selective quadriceps component activation in human subjects.
- Established relationships between knee extension moment and M-wave for each component.
- Calibrated EMG signals to determine load sharing during isometric knee extension.
Main Results:
- Vastus intermedius (VI) contributed the most (51.8-39.6%) to knee extension moment.
- Vastus medialis contributed the least (9.5-12.2%).
- VI's relative contribution decreased as total knee extension moment increased.
- Vastus lateralis and medialis contributions increased with higher knee extension moments.
- Absolute moment from each component consistently increased with total knee extension moment.
Conclusions:
- The central nervous system favors the centrally located vastus intermedius during submaximal isometric knee extension.
- Load sharing among quadriceps components is subject- and condition-specific.
- Understanding muscle recruitment strategies provides insights into neuromuscular control.