Unlike MR during normal sitting and standing, MR during fidgeting-like activities has not been well studied and documented. This could also contribute to the error in estimation. It has been demonstrated that MR during sitting while fidgeting could be 1.46 times the MR during motionless sitting, and MR during standing while fidgeting could be 1.69 times the MR during motionless standing (13). We believe that the underestimation of MR during fidgeting-like activities including the transition between activities is a major source of error, especially for chamber test during daytime, which should be investigated in the future.
For the chamber study, another source of error could be the assumption of a constant MR during sleep. We have previously shown that sleeping metabolic rate (SMR) is not constant and decreases with BMI during the sleep (29). Decrease of SMR and its relation to BMI:
MR at the beginning of sleep can be as much as 12% higher than the average SMR and at the end of sleep can be as much as 12% lower than the average SMR depending on the slope of decrease of SMR (29). So, simply using one value of SMR without considering the slope of the decrease could contribute to the error. By applying above slope equation, the MR estimated from IDEEA was recalculated. Although overall accuracy was increased by only 1% from 95.2 ± 2.3% to 96.2 ± 1.9%, a major improvement of SMR estimation was found (from 95.3 ± 2.7% to 99.0 ± 2.3%, more than 4%), proving that the slope of decrease of SMR is an important factor and should be considered in estimation of SMR.
This research was supported in part by NIH Grant NIDDK DK62152, P30KD2668, and DK07715.
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