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  • Author: Christopher C. Cheatham x
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Anthony D. Mahon and Christopher C. Cheatham

Ventilatory threshold (VT) is an important index of aerobic exercise function. The non-invasive nature of assessing VT and the fact that VT can be determined without obtaining a maximal exertion makes it broadly appealing to study in both healthy and diseased populations. Much of the understanding of the physiological and biochemical events underlying the occurrence and significance of VT is based on research involving adults. Several conclusions can be made from the studies which have examined VT in children. First, VT can be determined in a reliable manner. Second, heart rate deflection has been used as an alternative method to estimate VT and, based on limited information, appears to have reasonable accuracy. Third, although there is some evidence suggesting that VT (relative to maximal oxygen uptake [V̇O2max]) declines with maturation, the evidence is not overwhelming and it is based primarily on cross-sectional comparisons. Fourth, endurance training will increase VT in children to a greater extent than the increase in V̇O2max. Lastly, the physiological significance of VT and the metabolic consequences when exercise intensities exceeds VT are not well understood in children and are fruitful areas of research.

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Matthew T. Wittbrodt, Mindy Millard-Stafford, Ross A. Sherman and Christopher C. Cheatham

Purpose:

The impact of mild hypohydration on physiological responses and cognitive performance following exercise-heat stress (EHS) were examined compared with conditions when fluids were ingested ad libitum (AL) or replaced to match sweat losses (FR).

Methods:

Twelve unacclimatized, recreationally-active men (22.2 ± 2.4 y) completed 50 min cycling (60%VO2peak) in the heat (32°C; 65% RH) under three conditions: no fluid (NF), AL, and FR. Before and after EHS, a cognitive battery was completed: Trail making, perceptual vigilance, pattern comparison, match-to-sample, and letter-digit recognition tests.

Results:

Hypohydration during NF was greater compared with AL and FR (NF: -1.5 ± 0.6; AL: -0.3 ± 0.8; FR: -0.1 ± 0.3% body mass loss) resulting in higher core temperature (by 0.4, 0.5 °C), heart rate (by 13 and 15 b·min-1), and physiological strain (by 1.3, 1.5) at the end of EHS compared with AL and FR, respectively. Cognitive performance (response time and accuracy) was not altered by fluid condition; however, mean response time improved (p < .05) for letter-digit recognition (by 56.7 ± 85.8 ms or 3.8%; p < .05) and pattern comparison (by 80.6 ± 57.4 ms or 7.1%; p < .001), but mean accuracy decreased in trail making (by 1.2 ± 1.4%; p = .01) after EHS (across all conditions).

Conclusions:

For recreational athletes, fluid intake effectively mitigated physiological strain induced by mild hypohydration; however, mild hypohydration resulting from EHS elicited no adverse changes in cognitive performance.