The effect of hydration status on the measurement of lean tissue mass by dual-energy X-ray absorptiometry

Purpose

Athletes cycle between exercise and recovery. Exercise invokes changes in total body water from thermal sweating, muscle and hepatic glycogen depletion and metabolic water loss. Recovery from exercise results in rehydration, substrate repletion, and possible glycogen supercompensation. Such changes may corrupt the measurement of hydrated tissues, such as lean tissue mass (LTM), by dual-energy X-ray absorptiometry (DXA). The purpose of this study was to determine the effect of exercise and thermal dehydration and subsequent glycogen supercompensation on DXA-based measurement of body composition.

Methods

Twelve active adult (18–29 years) males exercised at 70% VO2max on a cycle ergometer in a thermal environment (30 °C) to induce a 2.5% reduction in body mass. Participants subsequently underwent a glycogen supercompensation phase, whereby a high carbohydrate diet (8–12 g/kg body mass/day) was consumed for a 48-h period. Whole-body DXA measurement was performed at baseline, following exercise and supercompensation.

Results

Following exercise, mean body mass decreased by −1.93 kg (95% CI −2.3, −1.5), while total LTM decreased by −1.69 kg (−2.4, −1.0). Supercompensation induced a mean body mass increase of 2.53 kg (2.0, 3.1) and a total LTM increase of 2.36 kg (1.8, 2.9). No change in total fat mass or bone mineral content was observed at any timepoint.

Conclusions

Training regimens that typically induce dehydration and nutrition regimens that involve carbohydrate loading can result in apparent changes to LTM measurement by DXA. Accurate measurement of LTM in athletes requires strict observation of hydration and glycogen status to prevent manipulation of results.

Keywords

DXAHydrationLean tissue massMeasurementGlycogenAthletes

Abbreviations

ANOVA

Analysis of variance

BM

Body mass

BMI

Body mass index

BMC

Bone mineral content

BMD

Bone mineral density

CI

Confidence interval

DXA

Dual-energy X-ray absorptiometry

FFM

Fat-free mass

FM

Fat mass

HR

Heart rate

LTM

Lean tissue mass

LSC

Least significant change

PAR-Q

Physical activity readiness questionnaire

ROI

Region of interest

TBW

Total body water

VO2max

Maximal oxygen uptake


Autor / Fonte:Clodagh M Toomey, William G McCormack, Phil Jakeman European Journal of Applied Physiology 2017 February 16
Link: http://link.springer.com/article/10.1007/s00421-017-3552-x