Influence of mild dehydration, fluid consumption and repetitive box lifting on body fluid movements

Date of Completion

January 2007

Keywords

Health Sciences, Occupational Health and Safety|Education, Health|Biology, Physiology

Degree

Ph.D.

Abstract

High intensity exercise changes the volume and concentration of fluid compartments. Repetitive lifting is a task performed in military, industrial, and construction settings, often performed with a time constraint and without an adequate water supply. The objective was to investigate the effects of repetitive box lifting (RBL) on body fluid movements under conditions of both fluid restriction (NF) and ingestion (F). Ten healthy male subjects (mean ± SD; age 21±2 y; body mass, 77.8±10.6 kg; height, 177±4 cm; body fat, 10.7±8.8%) were recruited from the University of Connecticut community. All procedures took place under mild environmental conditions (23°C, 50% relative humidity). Euhydration prior to morning testing was accomplished by subjects consuming an additional 420 mL of water on the evening before, and on the morning of testing. Bioimpedance spectroscopy (BIS) measurements were obtained after 20min of reclining, and a blood sample was taken from a forearm vein. Subjects then ate a standard breakfast followed by a 2-hour rest/exercise period (30min rest and 10min RBL, performed 3 times) and a 3-hour reclining recovery. No fluid was consumed during either recovery period. RBL consisted of self-paced lifting of a 20.5 kg box from the floor to a 1.32 m elevated platform. The exercise was intense, as evidenced by final plasma lactate concentration (15.2±2.7 mmol·L-1) and final heart rate (188±8 bpm). The change of posture from reclining during BIS measurements to standing for the rest/exercise period decreased percent change in plasma volume (%ΔPV) by 10.2±3.8%. Return to a reclining posture after the rest/exercise protocol significantly increased %ΔPV 22.7±5.6 and 19.1±4.2%, for F and NF respectively. During RBL for F and NF, %ΔPV was reduced significantly 9.7% from before to after RBL1, and then 5.4% to after RBL3. Plasma osmolality increased to 320±6 mOsm·kg-1 after each RBL, and then returned to pre-exercise values (301±5 mOsm·kg-1) during rest for both trials. A significant decrease in ICF and increase in plasma osmolality on the morning after the NF trial indicated dehydration. In conclusion, RBL induced mild dehydration that reduced intracellular fluid volume and increased plasma osmolality during 18-h of recovery. ^

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