Exercise-related hemoconcentration and hemodilution in hydrated and dehydrated athletes: An observational study of the Hungarian canoeists

Abstract

Hemoconcentration during exercise is a well-known phenomenon, however, the extent to which dehydration is involved is unclear. In our study, the effect of dehydration on exercise-induced hemoconcentration was examined in 12 elite Hungarian kayak-canoe athletes. The changes of blood markers were examined during acute maximal workload in hydrated and dehydrated states. Dehydration was achieved by exercise, during a 120-minute extensive-aerobic preload. Our research is one of the first studies in which the changes in blood components were examined with a higher time resolution and a wider range of the measured parameters. Hydration status had no effect on the dynamics of hemoconcentration during both the hydrated (HS) and dehydrated (DHS) load, although lower maximal power output were measured after the 120-minute preload [HS Hemoglobin(Hgb)Max median 17.4 (q1 17.03; q3 17.9) g/dl vs. DHS HgbMax median 16.9 (q1 16.43; q3 17.6) g/dl (n.s); HS Hematocrit(Hct)Max 53.50 (q1 52.28; q3 54.8) % vs. DHS HctMax 51.90 (q1 50.35; q3 53.93) % (n.s)]. Thirty minutes after the maximal loading, complete hemodilution was confirmed in both exercises. Dehydration had no effect on hemoconcentration or hemodilution in the recovery period [HS HgbR30' 15.7 (q1 15.15; q3 16.05) g/dl (n.s.) vs. DHS HgbR30' 15.75 (q1 15.48; q3 16.13) g/dl (n.s.), HS HctR30' 48.15 (q1 46.5; q3 49.2) % vs. DHS HctR30' 48.25 (q1 47.48; q3 49.45) % (n.s.)], however, plasma osmolality did not follow a corresponding decrease in hemoglobin and hematocrit in the dehydrated group. Based on our data, metabolic products (glucose, lactate, sodium, potassium, chloride, bicarbonate ion, blood urea nitrogen) induced osmolality may not play a major role in the regulation of hemoconcentration and post-exercise hemodilution. From our results, we can conclude that hemoconcentration depends mainly on the intensity of the exercise.

Fig 1. Schematic diagram of exercise protocols and sampling times.

Fig 2. Changes in hemoglobin and hematocrit parameters during the short protocol.

Rest: baseline values, sampling time before exercise. RER 0.9: median value 0.9 of the Respiratory Exchange Ratio (the aerobic range of the exercise). RER 1.0: median value 1.0 of the Respiratory Exchange Ratio (the anaerobic threshold of the exercise). Max: sampling time at the maximum exercise. R5’ and R30’: sampling times at the 5^th and 30^th minutes of the recovery period, respectively. The median, q1 and q3 quartiles, as well as the minimum and maximum values, are represented on the box plots. * Significant differences (p<0.05) from resting values.

Fig 3. Power/VO₂ and power/heart rate ratios as a function of time during the long dehydration protocol.

20’, 40’, …, 120’: averages of VO₂ and heart rate parameters measured over 20-minute workout periods, respectively. VM: sampling time at the maximum power after 120 min preload. The median, q1 and q3 quartiles, as well as the minimum and maximum values, are represented on the box plots.

Fig 4. Changes in major blood components influencing plasma osmolality during the long dehydration protocol.

Rest: baseline values, sampling time before exercise; 20’, 40’, …, 120’: sampling times at 20^th, 40^th, …, 120^th minutes of the exercise, respectively. VM: sampling time at the maximum power after 120 min preload; R5’ and R30’: sampling times at the 5^th and 30^th minutes of the recovery period, respectively. A major part of the osmolality is given by the change of sodium ions. To better represent visually the changes in the other components, we used an exponential magnification of the values, however, the numbers on the graphs show the actual values. The height of the columns and the numbers at the top indicate the changes in osmolality values.