Title page for ETD etd-07242012-040038
|Type of Document
||Lackland, William S.
||Effects of changes in plasma volume, osmolality and sodium levels on core temperature during prolonged exercise in heat
||Master of Science
||Health and Physical Education
|Herbert, William G.
|Gwazdauskas, Francis C.
|Sebolt, Don R.
- Body temperature
|Date of Defense
Six adult males of similar body composition and aerobic
capacity were tested to study the effects of changes in
plasma volume (PV), osmolality (OSM) and sodium (Na+) on
core temperature (Tc) under three exercise-thermoregulatory
stress conditions. The protocol consisted of 120 min of
upright stationary cycling at 50% V02max under neutral (24°
C, 50% RH) - euhydrated (NE), hot (35°C, 50% RH) -
euhydrated (HE), and hot-hypohydrated (HH) environmental
conditions. Venous blood samples were obtained at -30 min,
0 min and at 15 min intervals through a 30 min recovery and
were analyzed for blood hematocrit and hemoglobin, and for
plasma osmolality and sodium. Hematocrit and hemoglobin
were used to calculate relative changes in plasma volume.
Tc showed qualitatively similar linear increases in the
first 45 min of each trial. At 60 min, Tc in the NE trial
plateaued at 37.9°C. In the HE trial, Tc continued to show
a slight further increase after 45 min while in NE it became
significantly (p<0.05) lower at 45 min as compared to HE and
HH; at 60 min of exercise, the core temperature of all three
trials differed significantly (p<0.05), with HH being the
highest (38.3°C). Percent change in plasma volume was not
different between trials, but did show the greatest decrease
in all trials from O to 15 min of the exercise phase with at
least -4.3%. Osmolality was significantly different
(p<0.05) between the NE (X = 283.3 m0smol/kg) and the HH (X
= 292.5 m0smo1/kg). Plasma sodium was significantly
(p<0.05) higher for all intervals of HH (X = 137.9 meq/L) as
compared to the NE (X = 135.1 meq/L) and HE (X = 134.8
meq/L). These data suggest that core temperature (Tc)
increase in moderate intensity endurance exercise is less
related to a decreased circulating plasma volume, but is
more strongly associated with rising osmolality,
specifically the increase in the Na+ electrolyte, which
occur with progressive hypohydration.
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