Retentive capacity of power output and linear versus non-linear mapping of power loss in the isotonic muscular endurance test.

The limit of dynamic endurance during repetitive contractions has been referred to as the point of muscle fatigue, which can be measured by mechanical and electrophysiological parameters combined with subjective estimates of load tolerance for revealing the human real-world capacity required to work continuously. In this study, an isotonic muscular endurance (IME) testing protocol under a psychophysiological fatigue criterion was developed for measuring the retentive capacity of the power output of lower limb muscles. Additionally, to guide the development of electrophysiological evaluation methods, linear and non-linear techniques for creating surface electromyography (sEMG) models were compared in terms of their ability to estimate muscle fatigue. Forty healthy college-aged males performed three trials of an isometric peak torque test and one trial of an IME test for the plantar flexors and knee and hip extensors. Meanwhile, sEMG activity was recorded from the medial gastrocnemius, lateral gastrocnemius, vastus medialis, rectus femoris, vastus lateralis, gluteus maximus, and biceps femoris of the right leg muscles. Linear techniques (amplitude-based parameters, spectral parameters, and instantaneous frequency parameters) and non-linear techniques (a multi-layer perception neural network) were used to predict the time-dependent power output during dynamic contractions. Two mechanical manifestations of muscle fatigue were observed in the IME tests, including power output reduction between the beginning and end of the test and time-dependent progressive power loss. Compared with linear mapping (linear regression) alone or a combination of sEMG variables, non-linear mapping of power loss during dynamic contractions showed significantly higher signal-to-noise ratios and correlation coefficients between the actual and estimated power output. Muscular endurance required in real-world activities can be measured by considering the amount of work produced or the activity duration via the recommended IME testing protocol under a psychophysiological termination criterion. Non-linear mapping techniques provide more powerful mapping of power loss compared with linear mapping in the IME testing protocol.

Cutpoints for Muscle Mass and Strength Derived from Weakness or Mobility Impairment and Compared with Other Diagnostic Criteria in Community-Dwelling Elderly People.

We identified the strength cutpoints concerning mobility impairment, then identified the muscle mass cutpoints concerning weakness, and compared the results with other diagnostic criteria to develop the clinical diagnostic criteria associated with functional impairment. In 7583 elderly people, classification and regression tree (CART) and receiver operating characteristic curve (ROC) analyses were used for determining cutpoints for handgrip strength (HGS) and appendicular lean mass (ALM) indices associated with slowness or weakness. Logistic regressions were then used to quantify the strength of the association between muscle mass (or strength) categories and weakness (or slowness). The CART second cutpoints of muscle mass and strength indices were lower than those specified by the ROC method and were between those cutpoints determined by the 20th and Mean-2SD methods. After adjusting for covariates, the associations remained significant in handgrip strength categories defined by the CART and ROC cutpoints and HGS/BMI categories defined by the CART, ROC, and 20th cutpoints in men and women (P < 0.05), ALM, ALM/Ht2 categories defined by all four cutpoints (P < 0.05) and ALM/BMI categories defined by CART and ROC cutpoints in men (P < 0.05), and ALM and ALM/Ht2 categories defined by the CART cutpoints in women (P < 0.05). Our approaches resulted in a definition of weak strength as handgrip strength or HGS/BMI less than 26.55 kg or 1.114 in men and less than 16.45 kg or 0.697 in women and then defined ALM, ALM/Ht2, or ALM/BMI less than 18.92 kg, 7.08 kg/m2, or 0.795 in men and less than 15.04 kg, 5.99 kg/m2, or 0.517 in women as low lean mass.

Estimation of skeletal muscle mass by bioimpedance and differences among skeletal muscle mass indices for assessing sarcopenia.

BACKGROUND: It is crucial to assess age-related muscle mass changes and derived indices differences in geriatric medicine. We aimed to develop and validate four bioimpedance analysis (BIA) prediction equations against dual-energy X-ray absorptiometry (DEXA) and magnetic resonance image (MRI) in estimating skeletal muscle mass and to compare the differences among skeletal muscle mass indices, cutoff values, and corresponding prevalence rates of low muscle mass for assessing sarcopenia in Chinese adults. METHODS: We measured the height (Ht), weight (Wt), appendicular lean mass (ALM) or skeletal muscle mass (ASM), total lean body mass (LBM) or skeletal muscle mass (TSM) obtained using DEXA or MRI, and a multi-frequency BIA (BCA II;50, 250 kHz), in 371 adults aged 18.0-87.0 years. We also collected gender, age, Ht, Wt, and impedance indexes (Ht2/R50, Ht2/R250, R50/Ht2, R250/Ht2) from 30,500 adults aged 18-96 years living in China. Multiple regression analyses were used to derive four prediction equations by BIA, and double cross-validation techniques and Bland-Altman analyses were used to test agreement. Various muscle mass indices and prevalence rates were depicted by line plots in regard to age trends. RESULTS: Satisfactory results were found in the four prediction models as they had the larger R2 (0.833-0.930) values and low SEE (1.409-2.335 kg) values. The predictive variables included impedance indexes (Ht2/R50, R50/Ht2, R250/Ht2), gender, age, Wt, and Ht. The corresponding prevalence rates of low muscle mass exhibited significant differences according to the various muscle mass indices adjusted for Ht, Wt, or body mass index (BMI), in addition to the cutoff values based on two standard deviations (2SD) of young people or the lower 20% of the study group. CONCLUSIONS: The BIA equations have the potential to be applied as a practical method of quantifying skeletal muscle mass in Chinese adults. However, the operational methods that are most appropriate for determining the degree of low muscle mass that actually contributes to sarcopenia remains inconclusive.

Sarcopenia-related features and factors associated with low muscle mass, weak muscle strength, and reduced function in Chinese rural residents: a cross-sectional study.

Muscle strength and function declined more than the concomitant loss of muscle mass. Measures of muscle strength and function are an effective way to assess functional ability and physical health in older people. A healthy lifestyle such as physical exercise, good nutrition, and higher BMI can benefit older people. INTRODUCTION: The study investigated the characteristics of aging-related differences in appendicular lean mass (ALM/Ht2), handgrip strength (HGS), usual gait speed (UGS), repeated chair stands (RCS), Timed Up and Go (TUG) test, and their associated factors in 6703 rural residents. METHODS: We assessed their anthropometry, body composition, muscle strength and function, bone mineral density, blood pressure, and blood biochemical indices via clinical examination or laboratory tests and investigated demographic characteristics, lifestyle, medical history, physical activity, and dietary intake via questionnaire. Stepwise logistic regression was used to determine the associated factors of low muscle mass, weak muscle strength, reduced physical performance, and sarcopenia. RESULTS: The mean values of muscle strength and function decreased more rapidly with age than the mean values of muscle mass, especially in females. The prevalence of low ALM/Ht2, weak HGS, slow UGS, long RCS, long TUG, and sarcopenia increased (P < 0.01). Higher body mass index (BMI) and daytime sleep were associated with high ALM/Ht2. Comorbidity factors such as hypertension, bone mineral density loss, central adiposity, metabolic syndrome, and tumors were associated with the risk of weak muscle strength and reduced physical performance, while physical activity and better nutrition were associated with better muscle strength and physical performance. CONCLUSIONS: At the higher decades of life, the decline of muscle strength and function is greater than the loss in muscle mass. Measures of muscle strength and function are an effective way to assess functional ability and physical health in older people. Maintaining a healthy lifestyle by means such as physical exercise, good nutrition, and higher BMI throughout the course of life may be benefit older people by improving their muscle mass, strength, and function.

Decay kinetic properties of atoms in photonic crystals with absolute gaps.

Decay kinetic properties of a two-level atom near the band edges of photonic crystals (PCs) with absolute gaps are studied based on the Green's function expression for the evolution operator. The local coupling strength between the photons and an atom is evaluated by an exact numerical method. It is found that the decay behavior of an excited atom can be fundamentally changed by the variation of the atomic position: Weisskopf-Wigner and non-Weisskopf-Wigner decay phenomena occur at different atomic positions in the PCs as a result of a significant difference in the local coupling strength. Our finding implies that it is possible to engineer the luminescence spectrum by controlling the atomic position.