Related Experiment Video
Updated: Jan 13, 2026
Segmentation and Linear Measurement for Body Composition Analysis using Slice-O-Matic and Horos
Published on: March 21, 2021
Associations Between Skeletal Muscle Mass, Fat-Free Mass, and Saliva Osmolality: A Cross-Sectional Study
Ian P Winter1, Josie Burdin2, Patrick B Wilson1
1Human Performance Laboratory, School of Exercise Science, Old Dominion University, Norfolk, Virginia.
Objective:
This investigation evaluated the relationships between skeletal muscle mass (SMM), fat-free mass (FFM), and hydration status measured through saliva osmolality (SOSM). It was hypothesized that SMM and FFM would positively associate with SOSM.
Design:
A cross-sectional, observational study.
Setting:
Laboratory and field collection.
Participants:
Seventy-two adults (42 men, 30 women; 29.3 ± 10.6 years, 171 ± 9 cm, 78.8 ± 15.0 kg, 28.7% ± 8.1% body fat).
Independent Variables:
Skeletal muscle mass and FFM were measured through bioelectrical impedance analysis.
Outcomes:
Saliva osmolality was measured using the MX3 Hydration Testing System, a portable, noninvasive osmometer. Participants presented 2 saliva samples 3 to 5 minutes apart. Fluid intake was avoided for at least 5 minutes before sampling.
Results:
Linear regression analysis showed a nonsignificant association between SMM and SOSM (unstandardized B = 0.44, P = 0.144), as well as FFM and SOSM (unstandardized B = 0.23, P = 0.172). The adjusted analysis including covariates (age, sex, past 4-hour fluid intake, and time of sampling) showed nearly no effect, with insignificant associations between SMM and SOSM (unstandardized B = 0.98, P = 0.146) and FFM and SOSM (unstandardized B = 0.44, P = 0.173) remaining. Similarly, Spearman correlation coefficients between SMM and SOSM [ρ(72) = 0.10, P = 0.427] as well as FFM and SOSM [ρ(72) = 0.08 P = 0.487] were positive but nonsignificant and small.
Conclusions:
Despite growing evidence that urinary hydration biomarkers naturally vary with SMM and FFM, these 2 body composition variables seem to be insignificantly associated with hydration status according to SOSM. This may be related to relatively small concentrations of muscle metabolites (eg, creatinine, uric acid, urea) found in saliva.
