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Simultaneous Intracellular Recording of a Lumbar Motoneuron and the Force Produced by its Motor Unit in the Adult Mouse In vivo
Published on: December 5, 2012
Activity of motor units during concentric and eccentric contractions
T Moritani1, S Muramatsu, M Muro
1Human Performance Laboratory, Kyoto University, Japan.
American Journal of Physical Medicine
|December 1, 1987
Summary
Eccentric contractions require less motor unit (MU) recruitment and rate modulation than concentric contractions. This efficiency in eccentric muscle action may stem from better elastic energy utilization and muscle length-tension relationships.
Area of Science:
- Human Physiology
- Biomechanics
- Neuromuscular Physiology
Background:
- Understanding motor unit (MU) behavior is crucial for analyzing muscle force production.
- Concentric (CC) and eccentric (EC) contractions exhibit distinct physiological characteristics.
- Previous research indicates differences in muscle activation patterns between CC and EC.
Purpose of the Study:
- To investigate and compare motor unit activity in the biceps brachii during CC and EC.
- To analyze the influence of muscle length on MU recruitment and firing rates during different contraction types.
Main Methods:
- Utilized computer-aided intramuscular spike amplitude-frequency (ISAF) histograms.
- Performed surface electromyography (EMG) frequency power spectral analyses.
- Recorded simultaneous intramuscular and surface EMG signals across a range of elbow joint angles (30-150 degrees).
Main Results:
- Surface EMG showed significantly higher root-mean-square (RMS) amplitude and mean power frequency during CC, especially at shorter muscle lengths.
- Intramuscular recordings revealed greater MU activity and larger spike amplitudes during CC.
- ISAF histograms indicated significantly greater mean MU spike amplitude and frequency during CC compared to EC.
Conclusions:
- Eccentric contractions are associated with less pronounced MU recruitment and rate modulation.
- This reduced MU activation during EC may be attributed to economical tension development.
- Potential mechanisms include enhanced utilization of elastic energy and favorable length-tension relationships during EC.
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