Quantitative assessment of volumetric muscle loss: Dual-energy X-ray absorptiometry and ultrasonography.

The generalized skeletal muscle disorder that involves (in elderly subjects) the progressive loss of muscle mass and function has been defined sarcopenia, whereas the rapid-onset (traumatic or surgical) and focal (unilateral) loss of skeletal muscle with resultant functional impairment has been defined volumetric muscle loss. Different tools and approaches are commonly used in the clinical settings to quantify the loss of muscle or lean mass and to assess the consequent motor impairment. This review describes the technical principles and provides a summary of the main parameters that can be obtained to assess lean mass (and its distribution) or muscle size (and its structure) through the two imaging techniques most easily accessible and therefore frequently adopted in the clinical practice: dual-energy X-ray absorptiometry and muscle ultrasonography.

DXA-Derived Adiposity and Lean Indices for Management of Cardiometabolic and Musculoskeletal Frailty: Data Interpretation Tricks and Reporting Tips.

The proper assessment and follow-up of obesity and sarcopenia are relevant for the proper management of the complications of cardiometabolic and musculoskeletal frailty. A total body dual-energy X-ray absorptiometry (DXA) scan should be systematically incorporated in the rehabilitative routine management of patients with obesity and sarcopenia. In the former patients, the total body DXA can be used to assess the fat tissue amount and distribution, while in the latter patients, it can be used to quantify the reduction of appendicular lean mass and to investigate the inter-limb lean mass asymmetry. This tutorial article provides an overview of different DXA-derived fat and lean indices and describes a step-by-step procedure on how to produce a complete DXA report. We suggest that the systematic incorporation of these indices into routine examinations of the patients with obesity and sarcopenia can be useful for identifying the patients at risk for cardiometabolic and neuromuscular impairment-related comorbidities and for evaluating the effectiveness of pharmacological and rehabilitative interventions.

Contralateral effect of short-duration unilateral neuromuscular electrical stimulation and focal vibration in healthy subjects.

BACKGROUND: The "contralateral effect" phenomenon refers to the strength gain in the opposite, untrained homonymous muscle following unilateral training. Previous studies showed that neuromuscular electrical stimulation (NMES) of the right quadriceps facilitated maximal voluntary strength and efferent neural drive of the left knee extensors, while no previous study investigated the contralateral effect elicited by focal muscle vibration. AIM: The aim of this study was to investigate whether quadriceps NMES and focal vibration, when applied unilaterally, have the same potential to enhance the contralateral muscle strength and the associated neural drive. DESIGN: Randomized controlled experimental study. SETTING: University laboratory. POPULATION: Healthy subjects. METHODS: Subjects completed several maximal voluntary contractions (MVCs) of the left quadriceps (tested muscle) while the right quadriceps (treated muscle) received no conditioning stimulation (control condition), NMES or focal vibration. Paired supramaximal stimuli were delivered to the left quadriceps during and immediately after the MVCs to assess voluntary activation. The EMG activity of vastus lateralis, vastus medialis, and rectus femoris muscles of the left quadriceps was also concomitantly recorded. RESULTS: MVC torque and voluntary activation of the left quadriceps increased during contralateral NMES and vibration. A remarkable inter-individual variability was observed in the contralateral effect of NMES and vibration. In fact, MVC and voluntary activation increases were particularly evident in subjects "responders" to both treatments (who showed NMES-elicited increases in MVC and voluntary activation of 22.5% and 15.8%, respectively, and vibration-elicited increases of 13.1% and 10.7%, respectively). Moreover, we found that the increases in voluntary activation and EMG activity elicited by NMES were higher than those elicited by focal vibration. We also found that voluntary activation increases were higher in subjects presenting lower baseline levels of voluntary activation. CONCLUSIONS: The short-duration unilateral application of quadriceps NMES and focal vibration increased MVC torque and efferent neural drive of the contralateral homologous muscle in healthy subjects. CLINICAL REHABILITATION IMPACT: As the two physical therapy modalities can be useful to maximize motor unit recruitment contralaterally to the side of application, they could be incorporated in rehabilitation protocols when unilateral voluntary contractions are uncomfortable, painful or not feasible.