Post-exercise cold water immersion: effect on core temperature and ...

Eur J Appl Physiol (2013) 113:305–311 DOI 10.1007/s00421-012-2436-3

ORIGINAL ARTICLE

Post-exercise cold water immersion: effect on core temperature and melatonin responses Elisa Robey • Brian Dawson • Shona Halson Carmel Goodman • Warren Gregson • Peter Eastwood

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Received: 23 October 2011 / Accepted: 26 May 2012 / Published online: 16 June 2012 Ó Springer-Verlag 2012

Abstract To study the effect of post-exercise cold water immersion (CWI) on core temperature and melatonin responses, 10 male cyclists completed two evening (*1800 hours) cycling trials followed by a 15-min CWI (14 °C) or warm water immersion (WWI; 34 °C), and were then monitored for 90 min post-immersion. The exercise trial involved 15 min at 75 % peak power, followed by a 15 min time trial. Core (rectal) temperature was not different between the two conditions pre-exercise (*37.4 °C), post-exercise (*39 °C) or immediately postimmersion (*37.7 °C), but was significantly (p \ 0.05) below pre-exercise levels at 60 and 90 min post-immersion in both conditions. Core temperature was significantly lower after CWI than WWI at 30 min (36.84 ± 0.24 vs.

37.42 ± 0.40 °C, p \ 0.05) and 90 min (36.64 ± 0.24 vs. 36.95 ± 0.43 °C, p \ 0.05) post-immersion. Salivary melatonin levels significantly increased (p \ 0.05) from postexercise (*5 pM) to 90 min post-immersion (*8.3 pM), but were not different between conditions. At 30 and 90 min post-immersion heart rate was significantly lower (*5–10 bpm, p \ 0.01) after CWI than WWI. These results show that undertaking either CWI or WWI postexercise in the evening lowers core temperature below baseline for at least 90 min; however, the magnitude of decrease is significantly greater following CWI. The usual evening increase in melatonin is unaffected by exercise or post-exercise water immersion undertaken between *1800 and *2000 hours.

Communicated by Narihiko Kondo.

Keywords Rectal temperature Salivary melatonin Circadian rhythms High intensity exercise

E. Robey (&) B. Dawson School of Sport Science, Exercise and Health, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia e-mail: [email protected] S. Halson Performance Recovery, The Australian Institute of Sport, Canberra, Australia C. Goodman Sports Medicine, Western Australian Institute of Sport, Perth, Australia W. Gregson Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom P. Eastwood Centre for Sleep Science, School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, Australia

Abbreviations BM Body mass Bpm Beats per minute CV Coefficient of variation CWI Cold water immersion PP Peak power TT Time trial WWI Warm water immersion UWA The University of Western Australia

Introduction Many athletes regularly complete training sessions in the early evening, followed by the use of various post-exercise recovery techniques. Cold water immersion (CWI) is widely used, and has been shown to be beneficial to

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subsequent (24–48 h) performance (Ingram et al. 2009; Rowsell et al. 2009; Vaile et al. 2008b). The use of CWI for post-exercise recovery purposes originated from the practice of cryotherapy for local injury (Brukner and Khan 2000), with it’s application to a large surface area of the body based upon the noted effects of cryotherapy, primarily reducing blood flow and minimising inflammation (Burke et al. 2000). The majority of studies that have investigated the physiological effects of CWI, either in a resting (nonexercising) or post-exercise state (either in cool or hot environments) have shown that core temperature markedly decreases after CWI (Gregson et al. 2011; Halson et al. 2008; Peiffer et al. 2009; Sramek et al. 2000; Vaile et al. 2008b). Typically, these studies report a continual decrease in core temperature in the post-immersion period, with values lower than baseline and control conditions at the last time point measured (11–45 min post-immersion). A faster rate of core temperature reduction is also observed for CWI (as compared to no or warm water immersion: WWI) postexercise (Casa et al. 2007). Despite these general observations, the duration for which core temperature remains below resting/normal levels after CWI is unknown, but will depend on several factors, such as body composition, amount of body surface area immersed, water temperature and duration of exposure (Casa et al. 2007). Core body temperature also varies with normal daily circadian rhythms, usually peaking in early evening, with the nadir in early morning hours (Weinert and Waterhouse 2007). It is possible that CWI completed after evening exercise affects this normal circadian rhythm of core temperature. Furthermore, melatonin, a hormone produced in the pineal gland and frequently measured as a marker of the internal body clock (Waterhouse et al. 2005), has been shown to be strongly related with both core temperature and sleep propensity (Hughes and Badia 1997; Lack and Wright 2007). The circadian rhythm of melatonin secretion is inversely proportional to the normal core temperature cycle, with increases in melatonin promoting decreases in core temperature via cutaneous vasodilation (Waterhouse et al. 2005). In the early morning hours when core temperature is at its lowest point, melatonin can have a nocturnal peak 30 times higher than daytime levels (Atkinson et al. 2003). Whether levels of melatonin might be similarly influenced by evening CWI has not been thoroughly investigated. Only Kauppinen et al. (1989) have measured melatonin levels after CWI (in 9 winter swimmers, but without prior exercise) and observed no change in serum melatonin levels after two brief (20 s) immersions in 6 °C water. However, the relevance of this CWI procedure to current athletic practices, which are characterised by substantially longer periods of immersion, is limited.

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Eur J Appl Physiol (2013) 113:305–311

High intensity exercise in the early evening (before the normal nightly increase in melatonin secretion) advances the secretion of melatonin, whereas similar exercise performed at night (after the normal melatonin increase) delays this circadian-related increase (Buxton et al. 2003). However, the impact of post-exercise CWI, which rapidly lowers core temperature (albeit from elevated levels), on melatonin secretion in the evening is unknown. It is possible, that intense evening exercise followed by CWI could disturb the normal circadian control of core temperature and melatonin secretion, potentially affecting subsequent sleep quality and quantity. As sleep is widely regarded as the best recovery procedure for athletes (Samuels 2008), the potential impact of CWI on these responses is potentially very important. The purpose of this study was to investigate core temperature and melatonin responses to 15 min of CWI (14 °C) or WWI (34 °C) after fatiguing exercise, with measurements continued for 90 min post-immersion. Particular focus was given to ensure that exercise and CWI or WWI was conducted in the evenings, when both core temperature and hormonal response would be under the influence of normal (evening) circadian rhythms.

Methods Participants Ten male cyclists and triathletes (mean ± SD, 29.4 ± 2.5 years; body mass, 79.7 ± 7.2 kg; cycling peak power, _ 2 max , 56.1 ± 4.4 ml kg-1 min-1; sum of 418 ± 62 W; VO 7 skinfolds, 61.3 ± 16.4 mm) who were cycling at least 150 km per week were recruited for this study. Participants were required to complete two preliminary/familiarisation sessions and two experimental trials which were undertaken over a 4-week period. The study was approved by The University of Western Australia’s Human Research Ethics Committee and all athletes provided written informed consent prior to participation. Familiarisation sessions The first preliminary session involved a graded exercise cycle ergometer test (Evolution bicycles, Geelong, Aus_ 2 max and lactate threshold. This protocol tralia) to assess VO commenced at 150 W and increased every 3 min by 50 W, with a 1-min interval for microsample (earlobe) blood collection. Power outputs were measured using a customised computer program (Cyclemax version 6.3, School of Sport Science, Exercise and Health, University of Western Australia). Peak power was defined as the highest workload


_ 2 max test provided it was longer achieved during the VO than at least 1 min. Following this test, participants underwent CWI for 5 min (initial familiarisation). On a separate day, a second preliminary session was undertaken which required measurement of skinfolds according to The International Society for the Advancement of Kinanthropometry standards, followed by 10 min of CWI (final familiarisation). Experimental testing sessions During the third and fourth testing sessions participants were randomly assigned to undergo CWI or WWI. These testing sessions were performed at the same time of day (in the evening) and over consecutive weeks. Participants were required to keep a food and fluid diary for the 12 h prior to the first testing session and replicate this in the subsequent testing session. Prior to attending the laboratory, participants also consumed 15 mL per Kg BM of water to ensure adequate hydration. Participants were also required to keep exercise sessions consistent on the day prior to each experimental testing session and to abstain from caffeine, alcohol, sports drinks, bananas, chocolate and medications containing ibuprofen (as these products can interfere with the analysis of salivary melatonin) for 48 h prior to testing. Experimental trials were conducted in normal laboratory conditions (23 °C, 50 % RH) with a light intensity of *525 lux, as measured by a commercial light meter (Gossen Prosifix, Germany). Upon arrival at the laboratory participants were weighed (model CPW plus 200; Adam Equipment Pty Ltd, Perth, Australia; ± 0.05 kg) and a rectal probe (Physitemp, New Jersey, USA) inserted 10 cm past the anal sphincter. A Polar heart rate monitor (Kempele, Finland) was attached to the chest. Core temperature and heart rate values were recorded every 5 min for the duration of the trial. After 15 min of seated rest (to control for postural changes) participants provided a baseline salivary melatonin sample. Participants then performed a standardised warm-up at set percentages of peak power (PP), (3 min 25 % PP, 5 min 60 % PP and 2 min 80 % PP) determined from the graded exercise test. This was immediately followed by an exercise trial comprising 15 min at 75 % peak power (75 % PP) which was immediately followed by a 15-min time trial (TT), in which they completed as much work as possible. During the 75 % PP participants had access to power and time remaining data but when performing the TT participants were blinded to all outputs except remaining time (all cycling data were withheld from participants until the end of the study). Average power and total work were recorded and later analysed for both the 75 % PP and TT. This cycling protocol has been used

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previously to produce fatigue in athletes similar to that experienced in competition/training (Vaile et al. 2008a). Immediately after the TT, participants again provided a saliva sample. After 5 min (to change into their swimming costume), participants were immersed (seated) to the mid sternal level (arms not immersed) in an inflatable water bath, with temperature maintained at either 14 °C (CWI) or 34 °C (WWI) using a water chilling or heating unit (iCool Portacovery, Queensland, Australia) for 15 min. This is a commonly practiced CWI protocol, which has been shown to significantly reduce core body temperature following an exercise intervention (Peiffer et al. 2009; Vaile et al. 2008b). During the last minute of immersion another saliva sample was obtained. Participants then dried themselves and immediately changed into some warm clothing (the same for both trials) and were monitored for 90 min (seated), with further saliva samples taken at 30, 60 and 90 min post-immersion. Melatonin analysis Saliva was collected in salivette tubes (Serial No. 51.1534, Sarstedt, Nu¨mbrecht, Germany), with plain cotton swabs placed into the mouth and moved around until heavy, then placed back into the salivette tube. Samples were then centrifuged and the cotton plug discarded and frozen for later analysis of melatonin levels. Melatonin was assayed in 200 ul saliva by radioimmunoassay using kits from Buhlmann Laboratories, Allschwil, Switzerland, following the manufacturer’s instructions. These kits use the Kennaway G280 antibody (Vaughan 1993; Voultsios et al. 1997). Intra assay coefficient of variation (CV) was less than 10 % and the inter assay CV was 16 % at a concentration of 14.2 pM (Table 1). Statistical analyses Core temperature, heart rate and melatonin data for CWI and WWI were compared using 2-way repeated measures ANOVA (SPSS v18.0). When sphericity was violated, Greenhouse-Geisser tests were used. Where a significant interaction between condition and time was observed, differences between conditions were examined at each time point using paired t tests. Cycling data (total work and mean power in each phase) were also analysed using paired t tests. Correlation coefficients were also calculated according to the method described by Bland and Altman (1995) to examine the relationship between melatonin levels and core temperature. Significance was set at p B 0.05. For salivary melatonin, missing data points (n = 11/120) due to insufficient sample amounts were replaced with mean values.

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Table 1 Mean (±SD) cycling data recorded during cold (CWI) and warm (WWI) water immersion trials (n = 10) Condition

15 min 75 % peak power Total work (kJ)

15 min time trial Mean power (W)

Total work (kJ)

Mean power (W)

WWI

282.4 ± 40.8

313.8 ± 45.3

275.7 ± 35.7

305.8 ± 40.0

CWI

280.7 ± 39.2

311.8 ± 43.5

284.3 ± 33.3*

315.8 ± 37.0*

* CWI significantly (p \ 0.05) different from WWI

Total work and mean power during the 15-min cycle at 75 % PP were similar when performed before CWI and WWI (Table 1). There was a small but significant difference between conditions for the 15-min TT, with 3 % more work (p = 0.022) and 3 % greater mean power (p = 0.026) being achieved in the CWI trial (Table 1).

interaction between water condition and time (p = 0.007). Heart rate pre-exercise was *65 bpm and significantly increased during exercise to *180 bpm for both conditions (p = 0.000; Fig. 1). During immersion, heart rate decreased towards pre-exercise levels (*85 bpm) in both conditions. At 30 min post-immersion CWI heart rate was significantly (p = 0.001) lower than WWI (CWI 65 ± 10 bpm, WWI 76 ± 12 bpm) and similarly at 90 min postexercise (CWI 65 ± 13 bpm, WWI 70 ± 11 bpm; p = 0.033).

Core temperature

Salivary melatonin

There were significant main effects for both water condition (p = 0.021) and time (p \ 0.001), as well as a significant interaction between water condition and time (p = 0.023). Post hoc analysis revealed that core temperature was not significantly different between conditions preexercise (*37.4 °C), immediately post-exercise (*39.0 °C), pre-immersion (*38.8 °C) and immediately post-immersion (*37.7 °C) (Fig. 1). CWI core temperature was significantly lower (p = 0.011) than in WWI at 30 min (CWI 36.84 ± 0.24 °C, WWI 37.42 ± 0.40 °C), 60 min (CWI 36.62 ± 0.29 °C, WWI 37.07 ± 0.48 °C; p = 0.012) and 90 min post-immersion (CWI 36.64 ± 0.24 °C, WWI 36.95 ± 0.43 °C; p = 0.013). For both conditions, core temperature was significantly above pre-exercise levels at post- exercise (p \ 0.001) and pre-immersion (p \ 0.001), and significantly below pre-exercise levels at 60 (p = 0.002) and 90 min postimmersion (p \ 0.001).

Melatonin levels increased significantly with time across both conditions (p = 0.049); however, no significant main effects for either water condition or interaction between water condition and time existed (Table 2). Change in melatonin was not correlated with change in core temperature for either CWI or WWI (CWI r = 0.21, p = 0.11; WWI r = 0.22, p = 0.13).

Results Exercise tests

Heart rate There was a significant main effect for time (p \ 0.001) but not water condition (p = 0.073), plus a significant

Discussion The aim of this study was to determine the effect of fatiguing exercise followed by immersion in cold or warm water in the early evening on core temperature and melatonin responses. As anticipated, core temperature decreased rapidly after immersion in both warm and cold water, with CWI producing significantly lower core temperatures than WWI when measured at 30, 60 and 90 min post-immersion. While melatonin levels increased from post-exercise to 90 min post-immersion in both conditions, the magnitude of increase was not different between CWI and WWI at any time point post-immersion. Furthermore,

Table 2 Mean (±SD) salivary melatonin response (pM) to exercise and cold (CWI) and warm (WWI) water immersion (n = 10) Condition WWI

b

CWIb

Pre-ex

Post-ex

Post-imm

30 Post

60 Post

90 Post

5.7 ± 3.2

4.8 ± 0.8

5.5 ± 1.4

7.0 ± 5.3

11.3 ± 8.7

8.1 ± 5.0

4.9 ± 1.4

5.4 ± 1.3

5.8 ± 2.5

4.6 ± 0.6

8.8 ± 6.4

8.5 ± 5.1

There were no significant differences between WWI and CWI b

Significant main effect for time (p \ 0.05)

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Fig. 1 Mean (±SE) core temperature responses (°C) and heart rate responses (bpm) to exercise and cold (CWI) and warm (WWI) water immersion (n = 10). *CWI significantly (p \ 0.05) different from WWI. aSignificantly different (p \ 0.05) from pre-exercise measures in both conditions

no significant associations were noted between core temperature and melatonin responses for either condition. The acute impact of exercise and/or CWI on melatonin secretion has not been studied extensively. Our finding of no marked changes in salivary melatonin post-exercise or post-immersion supports those of Kauppinen et al. (1989), the only previous paper to have measured melatonin after CWI. Their stimulus was short duration (only two exposures of 20 s), very cold water immersion (6 °C) performed without prior exercise in the evening, in contrast to our much longer CWI (15 min in 14 °C) and prior fatiguing exercise. A key part of our study was to investigate core temperature and melatonin responses during the postimmersion phase after CWI. Athletes who train in the early evening may use CWI as a post-exercise recovery modality, and it is also likely that some would be attempting to sleep 60–120 min later. Exercise during daylight hours does not appear to affect the circadian phase of melatonin secretion (Buxton et al. (2003), whereas exercise in non-daylight hours may do so.

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Both Monteleone et al. (1990) and Buxton et al. (1997) reported that high intensity exercise at night (*2230 hours onwards) blunts the usual increase in plasma melatonin levels. Buxton et al. (1997) also reported that nocturnal (0000 hours) exercise results in a phase delay of the onset of normal melatonin secretion on the following day. However, Buxton et al. (2003) found that early evening high intensity exercise (*1830 hours) caused a phase advance of melatonin secretion on the next day. Our high intensity exercise bout was performed at *1800 hours, which may have preceded the normal rise in melatonin in the evening hours, at least during the period monitored (until *2130 hours). The presence of any phase advance the day after an experimental testing session was not investigated in the present study. The daily circadian rhythm of core temperature has been well documented, with a fall in core temperature usually in the evening hours (Lack and Wright 2007). The majority of studies that have investigated core temperature responses to water immersion have conducted testing during the day, when core temperature is under a different phase of the normal circadian cycle. Melatonin and core temperature appear to have an inverse relationship, with core temperature decreasing in the evening hours as melatonin levels increase, although a causal link has not been conclusively established (Atkinson et al. 2003). This natural decrease in core temperature may have been exaggerated in our study by water immersion (both CWI and WWI), with both 60 and 90 min post-immersion values being significantly below pre-exercise levels. As our trials were conducted at the athletes’ normal training time in the early evening, it was expected that melatonin levels would rise as the testing session proceeded. Our results here show an increase with time to 90 min post-immersion, but there were no differences between CWI and WWI. In the *2 h following exercise core temperature was rapidly lowered from *39 °C to below baseline levels after water immersion, but the lower core temperature caused by CWI had no impact on the measured melatonin responses. Similar salivary melatonin levels at approximately the same time of night (*2130 hours) have been reported by Ishibashi et al. (2010), but without prior exercise or water immersion. Therefore, the degree of any stimulus provided by exercise and/or CWI in the evening hours may not be enough to alter the normal circadian control of melatonin secretion. Of more potential importance was the lighting under which our experiment was conducted. Melatonin production is known to increase after exercise in the absence of bright light (Theron et al. 1984). Ishibashi et al. (2010) investigated melatonin responses to different light intensities (30 or 5,000 lux) over 4.5 h and under two different ambient temperatures (15 and 27 °C). They reported that salivary melatonin levels were suppressed by bright light,

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but that ambient temperature had no significant effect. Rectal temperatures were *37.0–37.2 °C during the light exposure, which occurred from 0000–0200 hours. In addition, even dim light (100 lux) may be enough to cause a circadian shift in humans (Duffy and Czeisler 2009). As our study was conducted in the laboratory under fluorescent lighting (*525 lux), the onset and degree of melatonin secretion may have been similarly affected by these conditions (Duffy and Czeisler 2009). However, performing the post-exercise water immersion and recovery here in a completely darkened room would have been unnatural for athletes, as this would not normally occur in their usual training environment. It is therefore likely that the light/ dark cycle is a more powerful stimulus affecting melatonin secretion than exposure to high intensity exercise and/or CWI for 15 min, including the impact of these on raising and then rapidly lowering core temperature. Further research is required to investigate this contention. In addition to the differences in core temperature responses to CWI and WWI, greater reductions in heart rate after CWI were also seen in the post-immersion period, as also reported by Al Haddad et al. (2010), who used similar water temperatures, but shorter immersion durations (5 min). They concluded that water immersion is a simple and efficient means of triggering post-exercise parasympathetic reactivation, with colder water temperatures being more effective. Harris (2005) has previously described the physiological changes during the transition from wakefulness to sleep, which includes a decrease in sympathetic activity and an increase in parasympathetic activity. Whether CWI augmentation of these responses has any subsequent effect on post-exercise recovery, performance and/or sleep is a topic for further research. Limitations Our study only investigated CWI and WWI post-exercise and hence had no true control condition (e.g. no exercise and/or no water immersion). This limits the interpretation of the data somewhat, as we did not have normal early evening values for both core temperature and melatonin. Similarly, our data collection only extended for 90 min post-immersion (finishing by *2130 hours) and may not have included the onset of normal nightly melatonin secretion. Future research into the effects of CWI post-exercise measuring circadian driven variables should employ a control condition and track any changes for a longer period post-immersion. Further, in the CWI trial there was 3 % more work completed in the TT than in WWI, although core temperature, heart rate and perceptions of fatigue and recovery were the same at post-exercise in both conditions. Therefore, this small difference is unlikely to have had any effect on subsequent core temperature and melatonin measures in the post-immersion phase.

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Conclusion In summary, CWI (15 min in 14 °C) after fatiguing exercise in the early evening produced lower core temperatures from 30 to 90 min post-immersion compared with WWI (15 min in 34 °C). Further, in both conditions, core temperature remained below pre-exercise levels. However, although salivary melatonin levels increased over the trial period, the water temperature did not influence this response. Whether the greater decreases in core temperature and heart rate produced here in the early evening by CWI have any impact on subsequent sleep quality and quantity, (considered to be the best post-exercise recovery strategy: Samuels 2008) remain unknown, but should be investigated further to ensure that athletes can maximise both training and competition performance. Acknowledgments The authors would like to acknowledge and thank iCool Sport for the loan of the chilling and heating units. Conflict of interest interest.

The authors declare they have no conflict of

References Al Haddad H, Laursen PB, Chollet D, Lemaitre F, Ahmaidi S, Bucheit M (2010) Effect of cold or warm water immersion on post-exercise heart rate recovery and heart rate variability indices. Auton Neurosci 156:111–116 Atkinson G, Drust B, Reilly T, Waterhouse J (2003) The relevance of melatonin to sports medicine and science. Sports Med 33(11): 809–831 Bland JM, Altman DG (1995) Calculating correlation coefficients with repeated observations: part 1–correlation within subjects. Br Med J 310:446 Brukner P, Khan K (2000) Clinical sports medicine, 3rd edn. McGraw Hill, Sydney Burke DG, MacNeil SA, Holt LE, MacKinnon NC, Rasmussen RL (2000) The effect of hot or cold water immersion on isometric strength training. J Strength Cond Res 14(1):21–25 Buxton OM, L’Hermite-Balriaux M, Hirschfeld U, Cauter E (1997) Acute and delayed effects of exercise on human melatonin secretion. J Biol Rhythms 12(6):568–574 Buxton OM, Lee CW, L’Hermite-Baleriaux M, Turek FW, Van Cauter E (2003) Exercise elicits phase shifts and acute alterations of melatonin that vary with ciracadian phase. Am J Physiol Regul Integr Comp Physiol 284:R714–R724 Casa DJ, McDermott BP, Lee EC, Yeargin SW, Armstrong LE, Maresh CM (2007) Cold water immersion: the gold standard for exertional heatstroke treatment. Exerc Sport Sci Rev 35(3):141–149 Duffy JF, Czeisler CA (2009) Effect of light on human circadian physiology. Sleep Med Clin 4(2):165–177 Gregson W, Black MA, Jones H, Milson J, Morton J, Dawson B, Atkinson G, Green DJ (2011) Influence of cold water immersion on limb and cutaneous blood flow at rest. Am J Sports Med. doi: 10.1177/0363546510395497 Halson SL, Quod MJ, Martin DT, Gardner AS, Ebert TR, Laursen PB (2008) Physiological responses to cold water immersion following cycling in the heat. Int J Sports Physiol Perform 3:331–346

Eur J Appl Physiol (2013) 113:305–311 Harris C (2005) Neurophysiology of sleep and wakefulness. Respir Care Clin N Am 11(4):567–586 Hughes RJ, Badia P (1997) Sleep-promoting and hypothermic effects of daytime melatonin administration in humans. Sleep 20(2):124–131 Ingram J, Dawson B, Goodman C, Wallman K, Beilby J (2009) Effect of water immersion methods on post-exercise recovery from simulated team sport exercise. J Sci Med Sport 12(3):417–421 Ishibashi K, Arikura S, Kozaki T, Higuchi S, Yasukouchi A (2010) Thermoregulatory effect in humans of supressed exogenous melatonin by pre-sleep bright-light exposure in a cold environment. Chronobiol Int 27(4):782–806 Kauppinen K, Pajari-Backas M, Violin P, Vakkuri O (1989) Some endocrine responses to sauna, shower and ice water immersion. Arctic Med Res 48(3):131–139 Lack LC, Wright HR (2007) Chronobiology of sleep in humans. Cell Mol Life Sci 64:1205–1215 Monteleone P, Maj M, Fusco M, Orazzo C, Kemali D (1990) Physical exercise at night blunts the nocturnal increase of plasma melatonin levels in healthy humans. Life Sci 47:1989–1995 Peiffer JJ, Abbiss CR, Nosaka K, Peake JM, Laursen PB (2009) Effect of cold water immersion after exercise in the heat on muscle function, body temperatures, and vessel diameter. J Sci Med Sport 12:91–96 Rowsell GJ, Coutts AJ, Reaburn P, Hill-Haas S (2009) Effects of cold-water immersion on physical performance between successive matches in high-performance junior male soccer players. J Sports Sci 27(6):565–573

311 Samuels C (2008) Sleep, recovery, and performance: the new frontier in high performance athletics. Neurol Clin 26:169–180 Sramek P, Simeckova M, Jansky L, Savlikova J, Vybiral S (2000) Human physiological responses to immersion into water of different temperatures. Eur J Appl Physiol 81:436–442 Theron JJ, Oosthuizen JMC, Rautenbach MM (1984) Effect of physical exercise on plasma melatonin levels in normal volunteers. S Afr J Med Sci 66:838–841 Vaile J, Halson S, Gill N, Dawson B (2008a) Effect of cold water immersion on repeat cycling performance and thermoregulation in the heat. J Sports Sci 26(5):431–440 Vaile J, Halson S, Gill N, Dawson B (2008b) Effect of hydrotherapy on recovery from fatigue. Int J Sports Med 29:539–544 Vaughan GM (1993) New sensitive serum melatonin radioimmunoassay employing the Kennaway G280 antibody: Syrian hamster morning adrenergic response. J Pineal Res 15:88–103 Voultsios A, Kennaway DJ, Dawson D (1997) Salivary melatonin as a circadian phase marker: validation and comparison with plasma melatonin. J Biol Rhythms 12:457–466 Waterhouse J, Drust B, Weinert D, Edwards B, Gregson W, Atkinson G, Kao S, Aizawa S, Reilly T (2005) The circadian rhythm of core temperature: origin and some implications for exercise performance. Chronobiol Int 22(2):207–225 Weinert D, Waterhouse J (2007) The circadian rhythm of core temperature: effects of physical activity and aging. Physiol Behav 90:246–256

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