Change in body mass accurately and reliably predicts change in body water after endurance exercise

• Published in: European journal of applied physiology 2009-04, Vol.105 (6), p.959-967
• Main Authors: Baker, Lindsay B., Lang, James A., Larry Kenney, W.
• Format: Article
• Language: English
• Subjects: Administration, Oral; Adult; Biological and medical sciences; Biomarkers - metabolism; Biomedical and Life Sciences; Biomedicine; Body Mass Index; Body Water - physiology; Breath Tests; Deuterium Oxide - administration & dosage; Deuterium Oxide - blood; Deuterium Oxide - urine; Exercise - physiology; Female; Fundamental and applied biological sciences. Psychology; Human Physiology; Humans; Male; Occupational Medicine/Industrial Medicine; Original Article; Osmolar Concentration; Physical Endurance - physiology; Predictive Value of Tests; Reproducibility of Results; Running - physiology; Specific Gravity; Sports Medicine; Sweat - metabolism; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-009-0982-0

This study tested the hypothesis that the change in body mass (ΔBM) accurately reflects the change in total body water (ΔTBW) after prolonged exercise. Subjects (4 men, 4 women; 22–36 year; 66 ± 10 kg) completed 2 h of interval running (70% V O 2max ) in the heat (30°C), followed by a run to exhaustion (85% V O 2max ), and then sat for a 1 h recovery period. During exercise and recovery, subjects drank fluid or no fluid to maintain their BM, increase BM by 2%, or decrease BM by 2 or 4% in separate trials. Pre- and post-experiment TBW were determined using the deuterium oxide (D 2 O) dilution technique and corrected for D 2 O lost in urine, sweat, breath vapor, and nonaqueous hydrogen exchange. The average difference between ΔBM and ΔTBW was 0.07 ± 1.07 kg (paired t test, P  = 0.29). The slope and intercept of the relation between ΔBM and ΔTBW were not significantly different from 1 and 0, respectively. The intraclass correlation coefficient between ΔBM and ΔTBW was 0.76, which is indicative of excellent reliability between methods. Measuring pre- to post-exercise ΔBM is an accurate and reliable method to assess the ΔTBW.