| Autor: |
Croce, Ronald, Miller, John, Smith, Wayne |
| Zdroj: |
Clinical Kinesiology (Online Edition); Summer2018, p7-17, 11p |
| Abstrakt: |
Incomplete activation, or activation failure, of motor units during maximum voluntary isometric contractions (MVICs) is often referred to as percent voluntary muscle activation (PVMA) and is defined as the inability of the central nervous system to maximally drive a muscle during voluntary muscular contractions. The purpose of the present study was to assess the interrelationship between PVMA and electrical and mechanical muscle amplitudes of the quadriceps' muscle as a function of knee-joint angle during MVICs. Nine young adult males performed MVICs in random order with the knee at 15, 55, and 95° flexion. PVMA was assessed using the interpolated twitch technique. Muscle amplitudes were estimated by electromyography (EMGAMP) and mechanomyography (MMGAMP) of agonist (vastus medialis, vastus lateralis, and rectus femoris) and antagonist (biceps femoris) muscles during MVICs. Results revealed a strong dependency of quadriceps' PVMA (p < 0.01) and EMG and MMG amplitudes (p < 0.01) on knee-joint position: PVMA was greatest and EMG and MMG amplitudes were lowest at the most shortened muscle position (15°) and vice versa at more lengthened muscle positions (55°, 95°), with the RF showing the greatest change in muscle amplitude. These data suggest that the ability to more fully activate the quadriceps at short compared to longer muscle lengths might partly compensate for the unfavorable force-length mechanics at the more extended position and consequent declines in muscle amplitude and force. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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