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Background: Weakness is a risk factor for physical limitations and death in older adults (OAs). We sought to determine whether OAs with clinically meaningful leg extensor weakness exhibit differences in voluntary inactivation (VIA) and measures of corticospinal excitability when compared to young adults (YAs) and OAs without clinically meaningful weakness. We also sought to estimate the relative contribution of indices of neural excitability and thigh lean mass in explaining the between-subject variability in OAs leg extensor strength.Methods: In 66 OAs (75.1 ± 7.0 years) and 20 YAs (22.0 ± 1.9 years), we quantified leg extensor strength, thigh lean mass, VIA, and motor evoked potential (MEP) amplitude and silent period (SP) duration. OAs were classified into weakness groups based on previously established strength/body weight (BW) cut points (Weak, Modestly Weak, or Not Weak).Results: The OAs had 63% less strength/BW when compared to YAs. Weak OAs exhibited higher levels of leg extensor VIA than Not Weak OAs (14.2 ± 7.5% vs 6.1 ± 7.5%). Weak OAs exhibited 24% longer SPs compared to Not Weak OAs, although this difference was insignificant (p = .06). The Weak OAs MEPs were half the amplitude of the Not Weak OAs. Regression analysis indicated that MEP amplitude, SP duration, and thigh lean mass explained ~62% of the variance in strength, with the neural excitability variables explaining ~33% of the variance and thigh lean mass explaining ~29%.Conclusion: These findings suggest that neurotherapeutic interventions targeting excitability could be a viable approach to increase muscle strength in order to reduce the risk of physical impairments in late life. [ABSTRACT FROM AUTHOR]

Fifteen healthy subjects (mean ± SD age = 27.6 ± 4.0 yrs) performed a submaximal isometric muscle action of the dominant leg extensors at 50% of the maximum voluntary contraction (MVC). Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis (VL) and vastus medialis (VM) during the muscle action and processed with a wavelet analysis designed specifically for EMG signals. The resulting EMG signals in each wavelet band were cross-correlated between the VL and VM. The results indicated significant coherence between the two muscles, with cross-correlation coefficient values that were generally above 0.5 and occasionally as high as 0.8-0.9. In addition, the strongest coherence was located primarily in wavelet bands 1-5 (center frequencies ranging from 6.90-92.36 Hz). Collectively, these findings demonstrated frequency-specific coherence between the VL and VM, thereby suggesting that the two muscles are likely not controlled independently by the central nervous system. The importance of the frequency-specific nature of this coherence is yet unknown, but may be related to inter-muscular coordination of a shared fiber type. [ABSTRACT FROM AUTHOR]

The article discusses research which investigated isometric strength, force steadiness, and surface electromyographic (EMG) responses of forearm flexors to concentric and eccentric exercise interventions. Topics explored include the muscle fatigue and damage associated with repeated eccentric exercises, the subject selection and experimental procedures performed, and the use of a customized software for evaluating EMG signal processing and force steadiness.

The article reports on research which investigated the strength and electromyographic (EMG) responses in exercised and nonexercised limbs after concentric (CON) vs. eccentric (ECC) exercise of the forearm flexors. Researchers evaluated 25 male subjects. They found that the CON exercise and ECC exercise interventions caused similar strength losses for the exercised arm and that there was also a strength loss in the contralateral nonexercised arm that was likely because of neural factors.