There were no between-diet differences in mean morning body mass values for LNA and MNA (days 1 to 18, p > .05, NS). Between-day differences (p < .001) were observed in the body mass of LNA, in that days 10 to 15 were significantly lower (p < .001) than day 8 (the initial day of heat exposure). The day-to-day body mass fluctuations in LNA and MNA may have involved changes in body fat, fat-free mass, or total body water. However, estimates of percent body fat showed no significant diet or day effects: day 1, 14 ± 1 percent (LNA), 14 ± 1 percent (MNA); day 8, 13 ± 1 percent (LNA), 14 ± 2 percent (MNA); day 17, 14 ± 1 percent (LNA), 15 ± 1 percent (MNA).

The mean morning urine specific gravity values for LNA and MNA (days 1 to 18) showed no between-diet differences (p > .05, NS). All mean urine specific gravity values (range: 1.016 to 1.023) indicated normal hydration status for both LNA and MNA on all days.

Figure 12-1 presents the concentrations of Na⁺ and K⁺ (mEq per liter) in the initial morning urine samples. The extremely low mean Na⁺ concentration on days 9 to 15 indicated that LNA adhered to the salt-restricted dietary regimen. The significant between-diet (LNA versus MNA) differences (p < .05 to .001) in Na⁺ and K⁺ are represented by asterisks. The differences in urinary Na⁺ were attributed to differential Na⁺ consumption and conservation, while differences in urinary K⁺ were of unknown origin and may have involved type I statistical errors of null hypothesis testing. Significant day-to-day differences in urinary Na⁺ (not shown in Figure 12-1) were identified for LNA between day 1 and days 3 to 18 (p < .05 to .001), as well as between day 8 and days 9 to 17 (p < .05 to .001). Significant day-to-day differences were observed for urine Na⁺ in group MNA between day 1 and days 2 to 18 (p < .01 to .001).

Mean values for hematologic variables in Table 12-2 represent preexercise samples drawn at 7:30 a.m. on days 8, 11, 15, and 17. A noteworthy between-diet difference in percent change in plasma volume (PV) occurred on days 11 and 15. Although the LNA group exhibited a significantly smaller (p < .05) expansion of PV than MNA on days 11 and 15, both treatment groups manifested a similar percent change in PV by day 17 (+12.3 percent versus +12.4 percent). Similar, significant between-day decreases (Table 12-2) were identified for total plasma protein in LNA and MNA (day 8 versus days 11, 15, 17; p < .01), even though PV expansion exhibited