## 3 Results and Discussion
### Nutritional Screening and Morphofunctional Assessment
#### 3.2.7 How to Assess Muscle Mass?  
**Recommendation 11**.: _GARIN suggests assessing muscle mass using any of the following techniques depending on the availability and feasibility of each medical equipment._  
Grade of recommendation GPP, (82%) Consensus.  
Depending on the techniques available, we can carry out a basic, intermediate, or advanced study of the patient's muscle mass at both diagnosis and follow-up (Table 4).  
\begin{table}
\begin{tabular}{l c} \hline \hline  & **Level of Study** \\ \hline Dual-energy X-ray absorptiometry (DEXA) & *** \\ \hline Magnetic resonance imaging (MRI) & ** \\ \hline Computed tomography (CT) & ** \\ \hline Muscle ultrasound & ** \\ \hline Bioelectric impedance analysis & ** \\ \hline Anthropometry & * \\ \hline \hline \end{tabular}
\end{table}
Table 4: Muscle mass assessment techniques according to the degree of complexity and availability.  
Comment:  
The gold standard for the assessment of bone mineral density and body composition is DEXA [15; 57; 59]. However, there are many studies in which bioelectric impedance analysis has been used, with a good correlation between fat-free mass and physical capacity, as well as a more severe staging of the disease, hospitalization for \(>\)7 days, and increased mortality at 6-9 months [11; 15; 35; 79]. A decrease in fat-free mass of \(<\)15 kg/m\({}^{2}\) in women and 16/17 kg/m\({}^{2}\) in men or \(<\)10 th percentile has been associated with increased mortality and morbidity [15; 35; 58].  
Different studies have defined low muscle mass with cut-off points of skeletal muscle mass index (SMI) of \(\leq\)8.50 kg/m\({}^{2}\) in men and \(\leq\)5.75 kg/m\({}^{2}\) in women [11]. A significant reduction in phase angle has also been described, especially in patients with sarcopenia [11]. In addition to these two techniques, the assessment of muscle mass has been evaluated in various studies using CT, MRI, and muscle ultrasound [79]. A relationship between decreased fat-free mass/lean mass index and increased disease severity and increased mortality has been reported. Thus, it has been reported in cross-sectional and retrospective studies that the pectoralis major muscle, assessed through CT (in terms of area and density), is associated with various body composition, respiratory, and prognostic variables in COPD. However, further research is required to standardize its use in clinical practice [82; 83; 84].  
Measurements of the anterior rectus femoris muscle (anteroposterior axis, area, etc.) at different levels (e.g., between the lateral epicondyle and the greater trochanter of the femur) have been performed by ultrasound, showing a significant correlation with the grip strength measured by dynamometry and the fat-free muscle mass by bioelectric impedance analysis [79].  
In terms of anthropometry, the most commonly used indices are brachial circumference and calf circumference measured in cm (pathological \(<\) 31 cm) [74].  
These techniques should always be performed by qualified professionals. In centers without experience in more complex techniques or in those where they are not available, anthropometric measurements such as circumferences and bioimpedance, if accessible, are recommended, in addition to collecting raw bioelectric data.