PLASMA VOLUME EXPANSION 24-HOURS POST-EXERCISE: EFFECT OF DOUBLING THE VOLUME OF REPLACEMENT FLUID

The effects of two volumes (1.5 L or 3.0 L) of commercially available electrolyte beverage (1.44 mM·L-1 Na+) taken during a 24-hour recovery period post-exercise, on plasma volume (PV) expansion 24-hours post-exercise were assessed. A simple random-order crossover research design was used. Subjects (n = 9 males: age 21 ± 4 years, body mass 80.0 ± 9.0 kg, peak incremental 60-second cycling power output 297 ± 45 W [means ± SD]) completed an identical exercise protocol conducted in hot ambient conditions (35oC, 50 % relative humidity) on two occasions; separated by 7-days. On each occasion, subjects received a different volume of 24-hour fluid intake (commercial beverage) in random order. In each case, the fluid was taken in five equal aliquots over 24-hours. PV expansions 24-hours post-exercise were estimated from changes in haemoglobin and haematocrit. Dependent t-testing revealed no significant differences in PV expansions between trials, however a significant expansion with respect to zero was identified in the 3.0 L trial only. Specifically, PV expansions (%) were; 1.5 L trial: (mean ± SE) 2.3 ± 2.0 (not significant with respect to zero), 3.0 L trial: 5.0 ± 2.0 (p < 0.05, with respect to zero). Under the conditions imposed in the current study, ingesting the greater volume of the beverage lead to larger mean PV expansion