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TABLE 4-3 Gastric Emptying During Ingestion of Different Beverages

Beverage (environment)

Gastric Residual Volume (ml)

% Drink Emptied

 

mean ± SEM

Glucose polymer (35°C)

487.6 ± 12.3

51.3 ± 1.2

Glucose (35°C)

587.0 ± 98.1*

41.3 ± 9.8*

Water (35°C)

412.1 ± 84.7

58.8 ± 8.5

Water (25°C)

208.8 ± 65.5

79.1 ± 6.5

* Significantly different (p < 0.05) from all other runs.

SOURCE: Adapted from Owen et al. (1986).

pared with only 59 percent when they performed the same exercise and ingested the same volume of water in the heat (35°C) (see Table 4–3). Neufer et al. (1989) made a similar observation and found a significant negative correlation between GE and rectal temperature. These investigators also found that hypohydration significantly reduced GE. The mechanism responsible for this reduction is unclear, but it is probably related to the thermal strain associated with hypohydration and exercise-heat stress. Exercise reduces splanchnic blood flow (Rowell et al., 1968) and elevates plasma beta-endorphin levels (Kelso et al., 1984), both of which could reduce GE (Konturek, 1980; Kowalewski et al., 1976). Also, it is known that elevations in core body temperature can reduce stomach and intestinal motility (Tsuchiya and Iriki, 1980; Tsuchiya et al., 1974).

INTESTINAL ABSORPTION

Is there any evidence that intestinal absorption is compromised during exercise-heat stress? Using the plasma accumulation of 3-O-methyl-D-glucose (active) and D-xylose (passive) from a solution ingested orally as measures of intestinal absorption, Williams et al. (1964) found that prolonged (4.5 hour) treadmill exercise (3.0 miles per hour) in the heat (38/27°C dry bulb/wet bulb) reduced active but not passive carbohydrate absorption. Maughan et al. (1990) also found evidence of reduced intestinal absorption during exercise. They measured the rate of plasma D2O accumulation from a beverage labeled with D2O and found that exercise at 61 percent reduced absorption measured at rest, and that absorption at 80 percent was less than at 42 percent and 61 percent .



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