Unreliable use of standard muscle hydration value in obesity

Intramuscular water content is assumed to be constant in humans independent of their anthropometric characteristics. To verify whether this assumption is correct, intramuscular water, proteins, glycogen, and both total and in tramyocytic triglycerides were measured in 51 samples of rectus abdominis m uscle obtained from 16 lean and 35 overweight and obese subjects (body mass index cutoff 24.9 kg/m(2)). Data (referred to as wet tissue) were analyzed by means of a composition model at the cellular level of the skeletal musc le (SM). The average SM water content was 76.3 +/- 3.3% in normal-weight in dividuals and 65.7 +/- 5.8% in obese subjects (P < 0.0001). Total triglycer ides were 5.5 +/- 2.3% in controls and 19.0 +/- 7.0% in obese subjects (P < 0.0001). The intramyocytic triglyceride fraction was also increased in obe se subjects. The composition model provides an explanation for the negative correlation between total triglycerides and intramuscular water, and some of the model parameters were determined from the experimental data. In conc lusion, although the hydration of fat-free SM mass may be unchanged in obes e subjects, the hydration of in toto muscle mass decreases as its lipid con tent increases.