Specific contribution of quadriceps muscle strength, endurance, and power to functional exercise capacity in people with chronic obstructive pulmonary disease: a multicenter study

Objective Various functional muscle properties affect different aspects of functional exercise capacity in people with COPD. The purpose of this study was to investigate the contribution of quadriceps muscle strength, endurance, and power to the 6-minute walking distance (6MWD) and the 1-minute sit-to-stand test (1STS) performance in people with COPD. Methods The study was a prospective, multicenter cross-sectional study. Anthropometrics, Medical Research Council (MRC) dyspnea scale, lung function, 6MWD and the 1STS number of repetitions were assessed. Isometric quadriceps strength (Strength-ISOM) and endurance (Endurance-ISOM), isotonic quadriceps endurance (Endurance-ISOT), isokinetic quadriceps strength (Strength-ISOKIN), and power (Power-ISOKIN) were assessed on a computerized dynamometer while functional quadriceps power was determined during 5 sit-to-stand repetitions (Power-5STS). Univariate and multivariate analyses were performed to determine the contribution of functional muscle properties on the 6MWD and the 1STS number of repetitions. Results The study included 70 people with COPD (mean % predicted FEV1 = 58.9 [SD = 18.2]). The 6MWD correlated with each functional muscle property, except the Endurance-ISOM. The number of repetitions during the 1STS correlated with each functional muscle property except isometric measurements. Multivariate models explained respectively 60% and 39% of the variance in the 6MWD and 1STS number of repetitions, with Power-5STS being the muscle functional property with the strongest contribution to the models. Conclusion Except for isometric endurance, quadriceps strength, endurance, and power were associated with functional exercise capacity in people with moderate COPD. Among these functional muscle properties, muscle power contributed the most to the 6MWD and 1STS number of repetitions, suggesting that muscle power is more relevant to functional exercise capacity than muscle strength or endurance in people with COPD. Impact Understanding the individual contribution of muscle properties to functional status is important to designing interventions. This study provides the guidance that muscle power may be more important to functional exercise capacity than muscle strength or endurance in people with COPD.

Sarcopenia – Endocrinological and Neurological Aspects

Sarcopenia in geriatric patients is often associated with or even caused by changes of the endocrine and nervous system. The multifactorial pathogenesis of sarcopenia and additional multimorbidity in geriatric patients makes it difficult to study distinct pathogenic pathways leading to sarcopenia. Patients suffering from diabetes, Cushing’s syndrome, chronic kidney disease, Klinefelter’s syndrome or motor neuron diseases, such as amyotrophic lateral sclerosis for example are known to have impaired muscle property and reduced physical performance. These patients are typically younger and suffer from conditions caused by a known molecular disease mechanism and a peculiar sarcopenic phenotype. Therefore, these sequelae can serve as prototypic disease models to study isolated endocrinological and neurodegenerative causes for sarcopenia. This review focuses on diseases whose etiopathogenesis of muscle impairment is known. The idea is to use these diseases as proof of principles to develop a classification algorithm of sarcopenia in the elderly to make a more mechanism-oriented therapy be possible.

Reconstruction of the Human Gastrocnemius Force–Length Curve in Vivo: Part 2—Experimental Results

For a physiologically realistic range of joint motion and therefore range of muscle fiber lengths, only part of the force-length curve can be used in vivo; i.e., the section of the force–length curve that is expressed can vary. The purpose of this study was to determine the expressed section of the force–length relationship of the gastrocnemius for humans. Fourteen male and fourteen female subjects aged 18–27 performed maximal isometric plantar flexions in a Biodex dynamometer. Plantar flexion moments were recorded at five ankle angles: −15°, 0°, 15°, 30°, and 40°, with negative angles defined as dorsiflexion. These measurements were repeated for four randomly ordered knee angles over two testing sessions 4 to 10 days apart. The algorithm of Herzog and ter Keurs (1988a) was used to reconstruct the force–length curves of the biarticular gastrocnemius. Twenty-four subjects operated over the ascending limb, three operated over the descending limb, and one operated over the plateau region. The variation found suggests that large subject groups should be used to determine the extent of normal in vivo variability in this muscle property. The possible source of the variability is discussed in terms of parameters typically used in muscle models.