Endurance athletes often ingest caffeine because of its reported ergogenic properties. Although there are a vast number of studies quantifying caffeine's effects, many research studies measure endurance performance using a time-to-exhaustion test (subjects exercise at a fixed intensity to volitional exhaustion). Time-to-exhaustion as a performance measure is not ideal because of the high degree of measurement variability between and within subjects. Also, we are unaware of any endurance sports in which individuals win by going a longer distance or for a longer amount of time than their competitors. Measuring performance with a time-trial test (set distance or time with best effort) has high reproducibility and is more applicable to sport. Therefore, the purpose of this review was to critically and objectively evaluate studies that have examined the effect of caffeine on time-trial endurance (>5 minutes) performance. A literature search revealed 21 studies with a total of 33 identifiable caffeine treatments that measured endurance performance with a time-trial component. Each study was objectively analyzed with the Physiotherapy Evidence Database (PEDro) scale. The mean PEDro rating was 9.3 out of 10, indicating a high quality of research in this topic area. The mean improvement in performance with caffeine ingestion was 3.2 +/- 4.3%; however, this improvement was highly variable between studies (-0.3 to 17.3%). The high degree of variability may be dependent on a number of factors including ingestion timing, ingestion mode/vehicle, and subject habituation. Further research should seek to identify individual factors that mediate the large range of improvements observed with caffeine ingestion. In conclusion, caffeine ingestion can be an effective ergogenic aid for endurance athletes when taken before and/or during exercise in moderate quantities (3-6 mg.kg body mass). Abstaining from caffeine at least 7 days before use will give the greatest chance of optimizing the ergogenic effect.

Objective: To assess existing original research addressing the efficiency of whole-body cooling modalities in the treatment of exertional hyperthermia.Data Sources: During April 2007, we searched MEDLINE, EMBASE, Scopus, SportDiscus, CINAHL, and Cochrane Reviews databases as well as ProQuest for theses and dissertations to identify research studies evaluating whole-body cooling treatments without limits.

Context: When assessing exercise hyperthermia outdoors, the validity of certain commonly used body temperature measuring devices has been questioned. A controlled laboratory environment is generally less influenced by environmental factors (eg, ambient temperature, solar radiation, wind) than an outdoor setting. The validity of these temperature measuring devices in a controlled environment may be more acceptable.Objective: To assess the validity and reliability of commonly used temperature devices compared with rectal temperature in individuals exercising in a controlled, high environmental temperature indoor setting and then resting in a cool environment.Design: Time series study. Setting: Laboratory environmental chamber (temperature 5 36.4 6 1.26C [97.5 6 2.166F], relative humidity 5 52%) and cool laboratory (temperature 5 approximately 23.36C [74.06F], relative humidity 5 40%).Patients or Other Participants: Fifteen males and 10 females.Intervention(s): Rectal, gastrointestinal, forehead, oral, aural, temporal, and axillary temperatures were measured with commonly used temperature devices. Temperature was measured before and 20 minutes after entering the environmental chamber, every 30 minutes during a 90-minute treadmill walk in the heat, and every 20 minutes during a 60-minute rest in mild conditions. Device validity and reliability were assessed with various statistical measures to compare the measurements using each device with rectal temperature. A device was considered invalid if the mean bias (average difference between rectal and device temperatures) was more than 60.276C (60.506F).Main Outcome Measure(s): Measured temperature from each device (mean and across time).Results: Conclusions: Even during laboratory exercise in a controlled environment, devices used to measure forehead, temporal, oral, aural, and axillary body sites did not provide valid estimates of rectal temperature. Only intestinal temperature measurement met the criterion. Therefore, we recommend that rectal or intestinal temperature be used to assess hyperthermia in individuals exercising indoors in the heat.Key Words: core body temperature, hyperthermia, tympanic membrane Key Points N As indicated by mean bias values, invalid estimates of rectal temperature (the ''gold standard'') were provided by forehead sticker, oral temperature, temporal temperature, aural temperature, and axillary temperature.N Intestinal temperature was the only measurement considered valid. N Successive intestinal, forehead sticker, temporal, and aural measurements demonstrated acceptable reliability.

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 FULL and PART conditions resulted in greater physiologic strain than the CON condition. These findings indicated that critical internal temperature and hypotension were concurrent with exhaustion during uncompensable (FULL) or nearly uncompensable (PART) heat stress and that anthropomorphic characteristics influenced heat storage and exercise time to exhaustion.