Influence of Hydration on Physiological Function and Performance During Trail Running in the Heat

Abstract

Context: Authors of most field studies have not observed decrements in physiologic function and performance with increases in dehydration, although authors of well-controlled laboratory studies have consistently reported this relationship. Investigators in these field studies did not control exercise intensity, a known modulator of body core temperature.Objective: To directly examine the effect of moderate water deficit on the physiologic responses to various exercise intensities in a warm outdoor setting.Design: Semirandomized, crossover design. Setting: Field setting. Patients or Other Participants: Seventeen distance runners (9 men, 8 women; age 5 27 6 7 years, height 5 171 6 9 cm, mass 5 64.2 6 9.0 kg, body fat 5 14.6% 6 5.5%).Intervention(s): Participants completed four 12-km runs (consisting of three 4-km loops) in the heat (average wet bulb globe temperature 5 26.56C): (1) a hydrated, race trial (HYR), (2) a dehydrated, race trial (DYR), (3) a hydrated, submaximal trial (HYS), and (4) a dehydrated, submaximal trial (DYS).Main Outcome Measure(s): For DYR and DYS trials, dehydration was measured by body mass loss. In the submaximal trials, participants ran at a moderate pace that was matched by having them speed up or slow down based on pace feedback provided by researchers. Intestinal temperature was recorded using ingestible thermistors, and participants wore heart rate monitors to measure heart rate.Results: Body mass loss in relation to a 3-day baseline was greater for the DYR (24.30% 6 1.25%) and DYS trials (24.59% 6 1.32%) than for the HYR (22.05% 6 1.09%) and HYS (22.0% 6 1.24%) trials postrun (P , .001). Participants ran faster for the HYR (53.15 6 6.05 minutes) than for the DYR (55.7 6 7.45 minutes; P , .01), but speed was similar for HYS (59.57 6 5.31 minutes) and DYS (59.44 6 5.44 minutes; P . .05). Intestinal temperature immediately postrun was greater for DYR than for HYR (P , .05), the only significant difference. Intestinal temperature was greater for DYS than for HYS postloop 2, postrun, and at 10 and 20 minutes postrun (all: P , .001). Intestinal temperature and heart rate were 0.226C and 6 beats/min higher, respectively, for every additional 1% body mass loss during the DYS trial compared with the HYS trial.Conclusions: A small decrement in hydration status impaired physiologic function and performance while trail running in the heat.Key Words: environmental physiology, dehydration, rehydration, core temperature, heart rate Key Points N The physiologic and performance decrements associated with dehydration that exist in laboratory settings also exist in field settings. N Methodologic challenges in the field setting make isolating these effects difficult.

The Effect of a Vocal Loading Task on Vocal Function Before and After 24 Hours of Thickened Liquid Use

“…The higher the urine density, the more dehydrated the individual. A USG of less than 1.010 g/ml is well hydrated, a urine density of 1.011.020 g/ml is minimally dehydrated and a urine density of 1.021-1.030 g/ml is significant dehydration [20]. Of the seven participants, only one participant was well hydrated following a 24-hour consumption of thickened liquids, four participants had mild dehydration, and two participants had significant dehydration.…”

“…Six of the participants exhibited an increase in USG following the 24 hour period of thickened liquid intake, thus indicating a decrease in hydration [20].…”

“…Measurement of urine specific gravity is frequently completed in research studies concerning the effects of hydration on athletic performance, and is considered to be a practical, noninvasive, and reliable parameter of hydration [19]. According to Casa et al [20], the National Athletic Trainer's Association recommends a urine specific gravity level of 1.020 g/ml prior to initiating exercise. This level was used as a benchmark of adequate hydration in the current study.…”

Effects of Acute Caffeine Consumption on Sodium-Aided Hyperhydration

“…Previous investigations have indicated that hypohydration can reduce exercise performance in the heat and lead to serious heatrelated illnesses [7,8]. While consumption of fluid during exercise can effectively reduce rates of dehydration, some individuals such as soldiers or endurance athletes participating in unsupported training sessions, may not have access to adequate fluid supplies and/or may have sweat rates that exceed the maximum rate of gastric emptying for water [9,10].…”

Low markers of muscle damage and inflammation following a 3-day trail run

“…1 These are generally regarded as more strenuous than road running due to the nature of the trails, which can involve diverse challenges including single track paths on steep ascends and descends in mountains, crossing rivers and running along grasslands and through forests. 2 Although physiological response to single-day trail running has been assessed, [1][2][3][4] the cumulative effects of multi-day trail running on markers of muscle damage and inflammation have not yet been reported. Prolonged endurance exercise causes muscle damage that initiates an inflammatory response and subsequent remodelling of muscle.…”