Abstract:
INTRODUCTION: The primary objective was to evaluate the effect of ad
libitum vs. restricted fl uid replacement protocol on hydration markers
and performance in selected military tasks. The secondary objective was
to determine if 300 ml h 1 could be considered a safe minimum fl uid
intake under the experimental conditions. METHODS: Data were collected
simulating a route march over 16 km. There were 57 subjects who
participated in the study. RESULTS: The mean pre-exercise body mass of
the ad libitum group was 70.4 13.3 (SD) kg compared to 69.3 8.9 kg
in the restricted group. The mean total fl uid intake of the ad libitum
group was 2.1 0.9 L compared to 1.2 0.0 L in the restricted group.
The ad libitum and restricted intake groups, respectively, lost a mean of
1.05 kg 0.77 (1.5%) and 1.34 kg 0.37 (1.9%). Calculated sweat rate
was 608 93 ml h 2 1 compared to 762 162 ml h 2 1 in the ad libitum
group. DISCUSSION: There were no signifi cant differences for either urine
specifi c gravity (USG) or urine osmolality (UOsm) before or after the
exercise. It is not clear whether fl uid intake and calculated sweat rates
are causally related or explained by their codependence on a third variable;
for example, the exercising metabolic rate. Thus, 300 ml z h 2 1 intake
could be considered a current safe minimum water intake for soldiers of
similar mass under similar experimental conditions, namely similar
exercise durations at equivalent exercise intensities in a moderate, dry
climate.
