The effects of creatine and glycerol hyperhydration on running economy in well trained endurance runners
© Beis et al; licensee BioMed Central Ltd. 2011
Received: 19 September 2011
Accepted: 16 December 2011
Published: 16 December 2011
Ingestion of creatine (Cr) and glycerol (Gly) has been reported to be an effective method in expanding water compartments within the human body, attenuating the rise in heart rate (HR) and core temperature (Tcore) during exercise in the heat. Despite these positive effects, a substantial water retention could potentially impair endurance performance through increasing body mass (BM) and consequently impacting negatively on running economy (RE). The objective of the present study was to investigate the effects of a combined Cr and Gly supplementation on thermoregulatory and cardiovascular responses and RE during running for 30 min at speed corresponding to 60% of maximal oxygen uptake in hot and cool conditions.
Cr·H2O (11.4 g), Gly (1 g·kg-1 BM) and Glucose polymer (75 g) were administered twice daily to 15 male endurance runners during a 7-day period. Exercise trials were conducted pre- and post-supplementation at 10 and 35°C and 70% relative humidity.
BM and total body water increased by 0.90 ± 0.40 kg (P < 0.01; mean ± SD) and 0.71 ± 0.42 L (P < 0.01), respectively following supplementation. Despite the significant increase in BM, supplementation had no effect on and therefore RE. Both HR and Tcore were attenuated significantly after supplementation (P < 0.05, for both). Nevertheless, thermal comfort and rating of perceived exertion was not significantly different between pre- and post-supplementation. Similarly, no significant differences were found in sweat loss, serum osmolality, blood lactate and in plasma volume changes between pre- and post-supplementation.
Combining Cr and Gly is effective in reducing thermal and cardiovascular strain during exercise in the heat without negatively impacting on RE.
Running economy (RE), which is defined as the sub-maximal oxygen consumption at a given running velocity, is an important physiological parameter as superior RE is essential for successful endurance running performance [1, 2]. In general, runners with good RE use less oxygen than runners with poor RE at the same absolute exercise intensity. RE appears to be influenced by many physiological factors  including hydration status. Coyle (2003) proposed that a -4 to -8% body mass (BM) deficit due to dehydration (i.e., the process of reducing body water) may lower the oxygen cost of movement , given that athletes who lose the most BM during a race are usually the most successful . Nevertheless, this theoretical paradigm contradicts the prevailing view of a body water deficit in excess of 2-3% BM constituting the level of dehydration that can adversely affect performance .
During exercise, skeletal muscle produces a significant amount of heat. When this metabolic heat production exceeds total heat loss, core body temperature (Tcore) rises. Consequently, endurance exercise performance in hot and dry environments can be limited by the increase in Tcore. An increase in Tcore during can be attenuated via the secretion and evaporation of sweat through the skin with inevitable body water loss. This decrease in body water is hypothesized to decrease plasma volume (PV) and consequently reduce the sweating response and therefore thermoregulation capacity, increase heart rate (HR) and reduce skin blood flow . Improved maintenance of PV is the overriding rationale for fluid ingestion during exercise by those supportive of the "cardiovascular model of dehydration" . However, proposed guidelines  are not always practical (e.g., difficulties providing adequate drinks during a race, athletes difficulties in drinking while running) and athletes typically refrain from consuming recommended amounts of fluids. Other means to expand PV can be by infusion of isotonic saline  with somewhat conflicting success [8, 9]. More recent approaches aimed at expanding body water compartments using hydrating agents such as creatine (Cr) and glycerol (Gly) have successfully attenuated the rise in Tcore and HR during exercise in heat [10, 11].
Cr has been shown to have hydrating effects [12, 13], although the exact process has yet to be established. Ingestion of 20 g·d-1 of Cr dissolved in 500 mL of water for 7 days have proved successful in attenuating the rise in HR and Tcore during exercise in the heat . These effects have been attributed to an increase in intracellular water (ICW), resulting in an increased specific heat capacity of the body [12, 13]. Moreover, whole body Cr retention is 60% higher when consumed with carbohydrate (CHO) compared to when Cr was consumed alone . Although the mechanism by which CHO enhances Cr uptake is not completely understood, consumption of 100 g per 5 g of Cr has been recommended for the effective improvement of Cr uptake . Like Cr, Gly has been found to be an effective agent in expanding the water compartments within the human body [11, 16]. Gly, seems to expand the ICW as well as the extracellular water (ECW) . In general, doses of 1.0-1.5 g Gly·kg-1 BM dissolved in 1.4 - 2.0 L of fluid 2.5 - 4 h before exercise  increase total body water (TBW) compartments and reduce thermal and cardiovascular strain during exercise in the heat.
Supplementation with combined hydrating agents such as Gly or Cr has consistently produced modest fluid retention of 400 - 800 mL [10–12]. Easton et al. (2007) were the first to add Gly to a Cr containing solution and demonstrate that a combination of the two hyperhydrating agents has an additive effect, as the addition of Gly to Cr significantly increased TBW more than Cr alone. Although the combination of the aforementioned hyperhydrating agents results in an increase in TBW and a reduction in certain cardiovascular and thermoregulatory responses , the BM increase due to enhanced hydration status could potentially reduce RE. The reduction of the energy cost of movement at a sub-maximal velocity by way of reducing BM to improve running performance is well known . For instance, it is noted that some marathon runners perform well despite dehydration of 4-8% BM . Coyle  proposed that this may occur because fluid loss (i.e., reduced body mass) lowers the oxygen cost of movement. On the other hand, the acute influences of hyperhydration on RE has not been investigation to date. Hence, the aim of the present study was to investigate the effects of hyperhydration induced by a combined Cr and Gly supplementation on thermoregulatory and cardiovascular responses and RE during 30 min of running at a running speed corresponding to 60% in cool (10°C with a relative humidity of 70%) and hot conditions (35°C with a relative humidity of 70%) in well trained male athletes. In cool ambient conditions were intended to minimize heat stress during exercise this enabling a focus on the effects of the altered BM induced by hyperhydration on RE at 60% . However, effects of hyperhydration on thermoregulatory and cardiovascular responses are also expected during exercise in hot and humid conditions; conditions typical of major sporting events (e.g., Olympic Summer Games). As such, it was hypothesized that an increase in BM and TBW induced by hydrating agents such as Gly or Cr would improve thermoregulatory and cardiovascular responses in line with previous findings but potentially negatively influence RE during running in the heat.
Fifteen trained male runners gave their written informed consent to take part in the present study which was approved by the University of Glasgow Ethics Committee and was performed according to the code of ethics of the World Medical Association (Declaration of Helsinki). One subject withdrew from the study before the final trial because of gastrointestinal distress during supplementation. Subjects were questioned as to their supplementation and training practices in order to ascertain that they had not supplemented with Cr for at least 8 weeks prior to commencing the study. Subjects were in good health at the time of testing, ran on a daily basis and participated regularly in competitive races. Athletes were also requested to maintain their typical weekly training regime during the course of the study.
Study design: Preliminary exercise tests
All subjects completed a test during an initial continuous incremental test at standard room temperature (20 - 21°C) and relative humidity (30 - 40%) on a motorized treadmill (PPS Med, Woodway, Germany) at 1% grade. After a warm-up period (depending on the runner), the subjects started running at 8 km·h-1 for 3 min in order to reach a steady state. In the next exercise bout the treadmill speed was set to 10 km·h-1 for 3 min and this procedure was repeated with 2 km·h-1 increments in running speed until volitional exhaustion of the subject. During the test expired gas samples (30 s collection time at the end of each bout) were taken using Douglas bag collection technique as is considered the gold standard method  and analyzed for O2% and CO2% (Servopro 4100 Gas Purity Analyzer, Servomex, UK) as well as analyzed for volume using a dry gas meter (Harvard, Kent, UK) and temperature of expired gases. Barometric pressure was measured using a standard mercury barometer. Additionally, a HR monitor (Polar Sports Tester, Polar Electro Oy, Kempele, Finland) was attached prior to each test and HR was recorded at the end of each bout. The measurement was used for calculating the intensity (60% of ) that subjects would perform during the actual tests. Running speed at 60% of (exercise intensity) was calculated using the linear relation between treadmill speed and .
Blood was drawn into dry syringes and 4 mL dispensed into a tube containing K3EDTA and the remaining 3 mL dispensed into plain tubes. Duplicate aliquots (100 μL) of whole blood from the K3EDTA tube were rapidly deproteinized in 1000 μL of ice-cold 0.3-mmol/L perchloric acid, centrifuged (8 min, 14000 rpm, HettichMicrocentrifuge, Germany), and frozen for later analysis of lactate using a standard enzymatic method  involving fluorimetric detection (Spectramax M2 Microplate Reader, Molecular Devices, Inc., US). The blood in tubes without anticoagulant was allowed to coagulate and then centrifuged; the serum collected was used to measure osmolality by freezing-point depression (Micro-osmometer 3300, Vitech Scientific, West Sussex, UK). The blood from the K3EDTA tubes was also analyzed for hemoglobin (cyanmethemoglobin method) and packed-cell volume (conventional microhematocrit method). All blood analyses were carried out in duplicate, with the exception of packed-cell volume, which was carried out in triplicate. PV changes were calculated from changes in hemoglobin and packed-cell volume relative to initial baseline values .
All data are expressed as the mean ± SD. All experimental variables (, , RER, RPE, TC, HR, Tcore) were tested for normality of distribution and compared between the two treatments using a repeated measures two-way analysis of variance (ANOVA) (i.e., pre- vs. post-supplementation). Students paired t-tests were carried out to test difference between each time pre- to post-supplementation when difference was detected using ANOVA. Statistical significance was set at P < 0.05 and in cases where significant differences were detected between time points pre- to post-supplementation, P-value was corrected using the Sidak adjustment. Responses at 10 and 35°C were analysed separately. Student paired t-tests were also used to examine the difference between pre- to post-supplementation for the rest of the comparisons. All statistical analysis was completed using the statistical package SPSS, version 15.0 (Statistica 8.0, Statsoft Inc., Tulsa, USA).
The 15 male subjects were trained distance runners with being 63.5 ± 5.2 ml·kg-1·min-1, age, 24 ± 5 yr; height, 180 ± 7 cm; BM, 69.5 ± 5.0 kg (values are presented as the mean ± SD).
Body Mass and Water Compartments
Oxygen consumption , carbon dioxide production , respiratory exchange ratio (RPE) during 30 min of running at 10 and 35°C conducted before and after supplementation.
Exercise time (min)
37.4 ± 2.4
37.6 ± 2.0
37.7 ± 1.8
38.7 ± 2.2
38.8 ± 2.7
38.9 ± 2.8
36.4 ± 2.8
37.4 ± 1.5
36.9 ± 1.7
37.7 ± 1.8
37.6 ± 2.2
38.4 ± 3.3
37.2 ± 2.4
39.5 ± 2.4
39.5 ± 2.3
40.3 ± 2.6
40.5 ± 4.4
41.2 ± 3.3
36.7 ± 2.4
37.9 ± 2.3
37.4 ± 3.2
38.4 ± 2.6
39.1 ± 2.1
38.5 ± 3.1
32.8 ± 1.7
33.7 ± 2.2
33.9 ± 1.4
34.4 ± 2.0
34.7 ± 2.5
34.4 ± 2.5
33.5 ± 3.1
34.6 ± 1.6
34.0 ± 1.7
35.0 ± 1.9
35.1 ± 2.0
35.0 ± 2.3
32.3 ± 2.8
34.7 ± 2.3
35.6 ± 2.3
35.3 ± 2.2
35.5 ± 3.2
35.5 ± 3.3
32.4 ± 2.5
33.9 ± 2.2
34.4 ± 2.4
35.1 ± 2.3
35.1 ± 2.3
34.5 ± 2.6
0.87 ± 0.03
0.89 ± 0.03
0.89 ± 0.03
0.88 ± 0.04
0.89 ± 0.04
0.88 ± 0.03
0.91 ± 0.05
0.93 ± 0.03
0.92 ± 0.03
0.93 ± 0.03
0.93 ± 0.03
0.92 ± 0.03
0.87 ± 0.05
0.88 ± 0.03
0.89 ± 0.03
0.88 ± 0.04
0.88 ± 0.05
0.86 ± 0.05
0.88 ± 0.03
0.89 ± 0.03
0.91 ± 0.03
0.91 ± 0.03
0.90 ± 0.03
0.89 ± 0.03
Rating of Perceived Exertion (RPE) and Thermal Comfort (TC)
Over the duration of running conducted at both 10 and 35°C significant (P < 0.05, ANOVA, time effect) increases were detected in RPE (Figure 2) and TC (Figure 3), while no significant differences were found between pre- and post-supplementation trials.
No significant changes were found in urine osmolality between the pre- (438 ± 306 mOsm·kg-1) and post-supplementation trials (448 ± 266 mOsm·kg-1).
Total Sweat Loss
During running at 10°C no significant differences between pre- and post-supplementation trials were observed in sweat loss (Pre: 0.3 ± 0.1 L; Post: 0.3 ± 0.1 L). Similarly, during running at 35°C no significant differences between pre- and post-supplementation trials were observed in sweat loss (Pre: 0.7 ± 0.2 L; Post: 0.8 ± 0.2 L).
Blood Lactate and Plasma Volume
During running at both 10 and 35°C no significant differences were found between pre- and post-supplementation trials in resting concentration of blood lactate. Furthermore, no significant increase in blood lactate was observed over duration of exercise. Additionally, during running at both 10 and 35°C no significant differences were detected between pre- and post-supplementation trials in PV changes.
Resting serum osmolality did not differ between pre- (268 ± 9 mOsm·kg-1) and post-supplementation (271 ± 19 mOsm·kg-1) trials. Additionally, no differences were observed between the post 10 and 35°C bouts and the resting values or between the treatments.
In general, subjects tolerated the supplementation protocol well, with only 1 report of gastrointestinal distress after supplementation who withdrew from the experimental process before completing the post-supplementation trial. This report is in line with the previous study by Easton et al. (2007), where 1 athlete had to also withdraw from the study due to similar reasons.
The novel finding of this study is that a previously established pre-exercise water loading strategy using a combination of hydrating agents such as Cr and Gly that significantly increased body water compartments and reduced cardiovascular (Figure 5) and thermoregulatory (Figure 6) responses during running at 35°C, had no effect on the oxygen cost of running at 60% of . The magnitude of change in BM following hyperhydration was similar to that previously reported in our laboratory  and by Kern et al. (2001). Somewhat smaller differences in body water compartments were observed in the present study compared to the previous investigation by Easton et al. (2007). For example, Easton et al  reported an increase of 0.9 L in TBW and 0.5 L in ICW after 7 days of supplementation. In the present study TBW and ICW were elevated by 0.7 and 0.3 L respectively after 7 days of supplementation. These differences could only be attributed to individual responses (i.e., level of "responders" to Cr supplementation as previously demonstrated) [13, 34] as similar protocols were utilised. In the present study, the retained water was dispersed in both the ICW and ECW. Despite the significant increase in BM and body water compartments and consequently improved thermoregulatory responses during exercise, no significant differences in any of the respiratory variables were found between the pre- and post-supplementation exercise trials. Therefore, the finding that a significant increase in BM did not negatively impact on RE of trained runners supports the use of hyperhydration during endurance running when running in hot and humid conditions although confirmatory results are required during faster running speeds typical of sporting competition (i.e., > 85% ).
Temperature and cardiovascular regulation during exercise in the heat do appear to be critically dependent on hydration status [35, 36]. In the present study, combined Cr and Gly supplementation induced significant hyperhydration and substantially attenuated the increase in HR at the end of the 30 min run at 35°C (Figure 5). This attenuation of HR during exercise was of similar magnitude to that previous reported by Easton et al. (2007). As free water in the form of sweat is primarily lost from plasma and since no differences were found in PV changes pre- and post-supplementation despite the increase in TBW, ICW and ECW, it can be suggested that the increase in other water compartments resulted in water moving towards the plasma due to an osmotic gradient. This in turn leaves the PV unaffected. It should be also noted that in order for blood volume to be maintained in conditions of significant thermal stain and therefore sweating, fluid loss is obtained in varying proportions from ECW as well as ICW body water compartments . Furthermore, as loss of body water increases during exercise in the heat as a result of sweating, Tcore also increases . Therefore, increasing body water could potentially result in better maintenance of Tcore during exercise in the heat. Nose et al.  reported a strong association between the loss of water in sweat and urine and the decrease in ICW after prolonged exercise in the heat. In the present study, Cr and Gly induced an increase in ICW and consequently, there was a significant attenuation in the rise of Tcore during exercise in the heat (Figure 6). It is possible that this Cr- and Gly-induced increase in ICW resulted in an increase of the specific heat capacity of the body .
Published studies to date appear to confirm the reduction of Tcore during exercise in the heat following Cr supplementation [12, 13, 19]. Conversely, when Gly was used alone, ICW was increased without significantly attenuating the rise in Tcore during the exercise period . The effects of Gly ingestion on Tcore and thermoregulation in general during exercise in the heat is equivocal, with several studies reporting a reduction in Tcore during exercise  and numerous other studies finding no such effect [16, 40]. In addition, several studies concluded that PV expansion has no effect on thermoregulatory responses or exercise performance during exercise in the heat [9, 41]. These conflicting results and assertions provide strong support that the thermoregulatory benefits exhibited with Gly ingestion in the present study did not arise from any PV expansion but most likely from an increase heat capacity of the body. Nevertheless, it should also be noted that these thermoregulatory benefits were exerted when Gly was co-ingested with Cr.
Despite the significant increase in TBW and consequently improvement in cardiovascular and thermoregulatory responses during exercise, no differences in were observed during running at 60% . Coyle proposed that a reduction in BM induced by dehydration would impact on RE during marathon running by reducing the oxygen cost of running . In contrast, hyperhydration should theoretically increase the oxygen cost of running and therefore RE. However, no such effect was found in the present study. Furthermore, there was no increase in over time during the trial at 10°C. The latter finding indicates that the subjects were working steadily at the calculated individual running speed corresponding 60% of . It should be noted that this relatively low intensity was chosen in order to ensure that the present data would be comparable with previous studies conducted under similar conditions . Furthermore, the relatively low intensity was chosen as to secure that all subjects could complete the experiment in the heat while it was high enough to observe possible adaptations in cardiopulmonary or thermoregulatory parameters encountered with supplementation. However, was increased during the trial in the heat. This was an expected effect as when exercising in hot environmental conditions, Tcore rises accordingly. It has been shown that with an increase in Tcore, (and therefore RE) also increases . Despite this observation, no discernable difference in between pre- and post-supplementation trials was reported. No other changes in any of the respiratory variables could be observed in the pre- and post-supplementation trials. Similar results have been reported in several other studies using Cr as the hyperhydrating agent  as well as during constant load exercise in the study by Easton et al. (2007) where hyperhydration was induced by Cr and Gly . The data from the present study suggest that an increase in BM of approximately 1.4% (average increase in BM in the present study) has no significant effect on . Whether such an increase in BM would influence running performance remains to be determined. Furthermore, as HR responses reflect those of , the finding that HR during exercise was not significantly different between pre- and post-supplementation trials conducted at 10°C is further evidence against any detrimental metabolic effect of the added BM induced by hyperhydration on RE.
A hyperhydration strategy that combines Cr and Gly supplementation for 7 days increased BM and TBW and consequently reduced cardiovascular and thermal strain but did not significantly affect the oxygen cost of running at 60% of at 35°C in trained runners. The finding that a significant increase in BM did not negatively impact on RE of trained runners, supports the use of effective hyperhydration strategies during endurance running when conditions so dictate (i.e., running in hot and humid conditions). Further studies are necessary however to confirm these findings during faster running speeds reflective of true performance.
The authors acknowledge Oleg Chepelin, Chao Wang and Andreas Anagnostopoulos for their major contribution in the data collection as well as John Wilson for his technical assistance.
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