Segmantal Bioelectrical Impedance Analysis Does Not Detect Chenges In Total Body Water After Vigoropus Exercise

Por: A. Stahn, Elmarie Terblanche e G. Strobel.

Athens 2004: Pre-olympic Congress

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Monitoring hydration changes in athletes is particularly important for maintaining exercise performance and general
health. Bioelectrical Impedance Analysis (BIA) has been suggested as a rapid, non-invasive and inexpensive technique
of measuring total body water (TBW) and fat-free mass. However, several studies have failed to show that BIA can
accurately monitor hydration changes caused by aerobic exercise [1,2]. It was hypothesized that performing segmental
measurements might overcome this drawback.

62 adults (29 men; 33 women) aged 18-33 years were randomly assigned to a treatment or a control group. The
treatment consisted of a 50-minute run on a treadmill at 75% of maximal oxygen uptake. Primary outcome measurements
were changes in TBW, whole body (WBIA) and segmental impedance (SBIA) indices at 50 and 200 kHz. Heart
rate, blood pressure (BP), electrolyte concentrations (Na+, P+, Ca2+ and Cl-), hematocrit (Hct), hemoglobin ([Hb]) and
surface temperature were studied as potential effect modifiers. All measurements were performed before, after exercise,
and 1 hour thereafter. Repeated Measures Multivariate Analyses of Variance (RMMAV) were employed to assess
between-group and within-subject changes over time. Univariate analyses and Scheffé post-hoc tests were used to
follow up any significant multivariate effects. Pearson correlations were calculated to examine the relationships
between impedance changes and changes of TBW. Multiple linear stepwise regression analysis was used to quantify the
effect of possible modifiers.

Neither changes in WBIA nor SBIA correlated significantly with changes in TBW. There were also no significant
differences between the control and the treatment group (P > 0.05). However, in contrast to WBIA, changes in SBIA
paralleled changes in TBW (Graph 1 and 2).

Discussion/ Conclusion
Both SBIA and WBIA do not seem to be suitable techniques for quantifying moderate hypertonic hypohydration as a
result of aerobic exercise in young healthy Caucasians. These findings could not be explained by changes in Na+, P+,
Ca2+ and Cl-, Hct and [Hb], HR and BP, and skin temperature. It is assumed that a redistribution of fluid volumes
between body segments predominantly concealed the changes in impedance measurements [3]. This is in accordance
with the results of SBIA which seems to monitor changes in TBW more closely than WBIA as SBIA provides a better
approximation of the biophysical model underlying impedance measurements and thus is less confounded by a regional
redistribution of body fluids.

[1] O’Brien C. et al. (1999). Med. Sci. Sports Exerc., 31 (10), 1466-1477.
[2] Collodel L. et al. (1997) Med Sport, 50, 197-202.
[3] Koulmann N. et al. (2000). Med. Sci. Sports Exerc, 32, 857-864

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