As shown by both classic BIVA14
and the newly proposed specific approach,17
sarcopenic individuals were characterized by peculiar bioelectrical characteristics. In particular, classic BIVA recognized a lower phase angle and a longer impedance vector (due to the higher values of R/H) in sarcopenic individuals than in nonsarcopenic individuals. These results are consistent with the theoretical expectations of BIVA, as the sarcopenic mean impedance vector was located in the region of the RXc graph corresponding to lean individuals.14
In general, a low phase angle is related to a low body cell mass14
and to a high ECW/ICW ratio.21
Castillo-Martínez et al24
found a low phase angle and a high R/H (but also, differently from us, low Xc/H values) in cachectic individuals. Norman et al16
obtained a similar displacement of the impedance vector in patients with low hand grip strength. The authors interpreted such vector migration as indicative of low muscle function and suggested the use of BIVA in place of hand-grip strength tests when subjects are not cooperative.16
We cannot exclude the possibility that the peculiar bioelectrical pattern found in sarcopenic individuals could be due to a loss of muscle function, as Norman et al16
suggest. However, it is certainly associated with the lower body cell mass, FFM in particular, of sarcopenic individuals.
Noticeably, the significant relation between phase angle and the reliable biomarkers of body cell mass (ASM and SMI) obtained in this research confirm the expectations of Piccoli et al.14
These results are also in accordance with those of Kyle et al,25
who found a similar positive relation between reactance and ASM, but disagree with those of Pietrobelli et al,26
whose results showed that phase angle does not add significantly to BIA prediction models. Moreover, the lower phase angle of sarcopenic individuals can be related to a higher ECW/ICW ratio21
(Buffa et al, unpublished data, 2012), a parameter that can be associated in relation with BCM,27
which is, in turn, related to muscle mass.28
According to specific BIVA, and in particular on the basis of similar R sp values in sarcopenic and nonsarcopenic individuals, the mean differences in the relative quantity of fat mass were not evident (with a p
-value slightly above the significance level in women). In effect, the FMDXA
% mean differences were not significant in men, while in women they reached a significance level of p
< 0.05 (higher FMDXA
% values in nonsarcopenic women).
Interestingly, BMI was significantly higher in the “normal” groups (p
< 0.01 in both sexes), showing that, as recently clearly stated by Thibault and Pichard,13
it is more an indicator of body mass than body composition.
Specific BIVA, but not classic BIVA, recognized bioelectrical differences between sarcopenic and sarcopenic obese men, as shown in . The higher values of R sp in sarcopenic obese individuals indicated a greater proportion of fat in their bodies (). Moreover, the impedance vectors of all sarcopenic obese individuals were located in the upper right quadrant (), a region of the specific tolerance ellipses that was recognized as corresponding to obesity17
(Buffa et al, unpublished data, 2012). The validation of appropriate cut-offs in a larger reference sample would confirm the suitability of this procedure for the diagnosis of sarcopenic obesity.
With respect to other standard clinical methods, such as DXA or MRI, BIVA has some methodological advantages. It can easily be performed by a single operator very quickly (less than 10 minutes per patient), is completely safe because no radiation exposure is needed, and has low maintenance and operational costs.
With respect to other simple adiposity indexes, such as WC and BMI, BIVA appears more adequate in recognizing body composition variations. BIVA analyzes electrical properties of tissues and is sensitive to changes of body cell mass and hydration;14
has been shown to accurately evaluate the relative amounts of fat and FFM, so it is probably sensitive to skeletal muscle fat infiltration and inflammatory states. According to Siervo et al,29
BMI and WC showed the worst performance when classifying sarcopenic obesity in a large sample of women. Moreover, the visceral fat distribution detected by WC is a dimorphic character more pronounced in men than in women; in fact, even though in the present research WC showed significant differences between sarcopenic and sarcopenic obese men (), in women the correlation of WC with FM% (r: 0.42, p
< 0.01) was lower than the correlation between R sp and FM% (r: 0.62, p