Consistent hydration for sustained performance -
As illustrated in Fig. To maintain consistency, participants performed this test oriented in the same position, and using the same hand grips for support during each of the measurements.
Participants were also vigorously encouraged to exert maximal effort on each measurement by the same individuals. When the participants were comfortable and ready to perform the measured test, they indicated this to the machine by holding their leg in a fully contracted position for several seconds, signaling the measurement process detailed above to proceed.
Hydration status was monitored using salivary osmolality. Several different measurements can be used to assess hydration, including serum, saliva, and urine osmolality, and urine volume and specific gravity, and the most appropriate measurement depends on the mode of dehydration, and the frequency of the measurement.
Previous studies have demonstrated that, for repeated measurements during active dehydration i. exercise in the heat, salivary osmolality is an accurate, non-invasive method to measure ECF osmolality [ 18 ].
Saliva was collected from the oral cavity, first as a passive expectorant unstimulated [ 17 , 19 ], and then following mechanical stimulated orofacial movement chewing on a cotton swab. All samples, both stimulated and unstimulated were then vortexed to homogenize the samples.
This was done immediately after sample collection to prevent sample spoilage. In addition to daily calibrations, the osmometer was calibrated prior to each new biological sample.
All values are presented as mean SD. Body Mass Index BMI was calculated using the following equation:. Body Surface Area BSA was calculated based on the following equation [ 20 ]:. To compare heart rate, body weight BW , BMI, BSA, and tympanic temperature at baseline and peak, the measured values in each individual were averaged across the three arms of the study.
Salivary osmolality S osm was plotted against percent body mass loss; body mass loss was calculated as the difference in body mass after completion of the dehydrating exercise, from body mass at trial initiation. This value was divided by body mass at trial initiation and expressed as a percentage.
Differences in the slopes of the regression lines between the groups were calculated using one-way analysis of variance ANOVA with Bonferroni post hoc correction for multiple comparisons.
The return of S osm to baseline during the Hydration Protocol was best fit by a mono-exponential one-phase decay model where,. Statistical calculations were calculated using commercially available software GraphPad Prism version 5.
All other comparisons were completed using a repeated measures 2-way ANOVA followed by a post-hoc Bonferroni analysis.
No non-parametric tests were necessary, as all data were normally distributed. Female participants were significantly less in height when compared to male counterparts Considering the significant difference in height, BW However, this difference was eliminated in the calculated BMI; females had a BMI of Although baseline heart rate trended higher in females For each min bout of exercise, we recorded peak heart rate and subsequently averaged these values to arrive at a single peak heart rate.
We saw no significant impact of sex on peak heart rate, and no interaction between sex and exercise on peak heart rate. Tympanic temperature as an indicator of core temperature was also recorded throughout the exercise protocol.
Despite being subjected to exercise and moderate heat stress, both female For each saliva sample unstimulated and stimulated , we determined salivary osmolality S osm and plotted S osm against the percent of body mass lost.
For display purposes, we represent the data as binned samples ± standard deviation S. Stimulated and unstimulated S osm were significantly positively correlated with percent of body mass loss for both females and males. The relationship of S osm and percent body mass loss was not different between females and males.
Salivary osmolality as a function of body mass loss. Individual measures of salivary osmolality were averaged from the three trials. No differences between Females and Males were detected, nor was there an interaction between sex and time point of data collection. Two-way ANOVA with post-hoc Bonferroni analysis.
No significant differences in baseline S osm among study groups based on fluid designation were detected, validating that participants began each arm of the three trials at a similar hydration level.
Baseline S osm was not effected by sex in the stimulated females Similar to baseline, peak S osm was not significantly impacted by either study group designation or sex in the stimulated females Moreover, there was no significant interaction between these factors on peak S osm.
However, this elevation in S osm was not affected by the sex of the participant Fig. Subsequent comparison of the mean values for each participant demonstrated that males took less time Based on the averaged values of sweat rate for each participant, females Peak S osm steadily declined and returned to baseline S osm values before completion of the saliva collection time during the rehydration phase.
The same trend of significance was seen whether S osm was taken from the stimulated or the unstimulated samples. Rate of salivary osmolality recovery during fluid hydration following dehydrating exercise protocol. Salivary osmolality was fit with a single exponential decay one-phase decay starting with peak salivary osmolality against real time.
a representative one-phase decay fit to salivary osmolality recovery during fluid hydration. Fluid was ingested in two phases indicated by the arrows. A repeated-measures two-way ANOVA determined a significant impact of fluid on rate parameters of hydration that was not impacted by sex.
Overall, males generated greater peak torque extension at baseline when compared to females However, the loss of peak torque reached significance only in males 9.
Impact of dehydration and hydration on lower body muscle performance. a Averaged values across experimental groups for peak torque extension Nm at Baseline and Post-Ex in Females and Males. The goal of the study was to evaluate parameters of dehydration and associated performance deficits due to dehydrating exercise, and then to determine if hydration and muscle performance recovery was dependent on fluid type.
Secondarily, we observed potential sex differences in these parameters, although the study was not explicitly powered for such comparisons. Our observations on increases in heart rate are consistent with most [ 21 , 22 , 23 , 24 ], but not all [ 25 ] studies in the literature reporting statistically similar increases in heart rate for females and males during strenuous exercise.
It has been suggested that males and females may differ in heart rate response to exercise, due in part to differences in exercise capacity, with men being able to reach higher exercise intensities, and therefore generate larger changes in heart rate during exercise [ 25 ].
It has also been suggested that a bias may exist in research personnel against pushing females as hard as males during exercise [ 25 ], and that males may put in a higher degree of effort during exercise than females [ 22 ], both of which could show confounded sex differences in peak heart rate.
Indeed, we informally observed that males tended to exercise at a higher workload than females during our exercise study. However, our study, as well as another [ 22 ] showed similar max heart rates in females as males, despite the appearance of a difference in effort, indicating that males and females demonstrated similar exertion.
We observed a slight but statistically insignificant increase in tympanic temperature throughout the duration of the exercise protocol in men and women, with no differences between the sexes. This lack of difference between sexes was not surprising, because although males and females differ in some specific aspects of thermoregulation sweat rate and evaporative cooling efficiency during exercise in the heat, it is thought that females and males are able to maintain body temperature with similar efficiency [ 26 ].
However, we did not expect to see an overall lack of significant increase in body temperature after exercise, since much of the literature supports the idea that exercise, heat, and dehydration impair thermoregulation [ 3 , 11 , 26 ].
More likely, acclimation to exercising in hot conditions may be the reason for this observation. Heat acclimation may provide the athlete with the benefit of expanded erythrocyte volume, and plasma volume, both of which have the potential to improve thermoregulatory ability in athletes [ 29 ].
We did not account for heat acclimation in this study, but it is reasonable to infer that some or all of the study participants had some level of heat acclimation living in Arizona, a region with a hot, dry climate throughout most of the year.
Average baseline S osm was not different between males and females. Furthermore, we confirmed a significant positive correlation between percent body mass loss through sweat dehydration and S osm for both males and females, as expected during intense exercise in the heat.
These were important observations, because they indicate that participants started at the same hydration level and executed a similar amount of exercise during each trial.
Although power output was not measured, we observed that men may have had higher average power output and tended to use greater resistance throughout the workout, consistent with findings showing higher aerobic workload capacity in men compared to women [ 30 ].
A higher power output in males could be one reason for the observed shorter time-to-dehydration than females. This difference in time-to-dehydration could also be attributed to a faster general sweat rate in males than in females, mainly due to greater body surface area and lower surface area-to-mass ratio, and greater metabolic heat production in males than in females [ 30 , 31 ].
Although females generally have a greater number and density of eccrine sweat glands than men [ 30 ], the per-gland sweat secretion rate is a larger contributing factor to overall sweat rate than the number or density of sweat glands [ 31 ]. Sweat secretion rate per gland varies inter- and intra-individually, but it is possible that this factor may be partially responsible for this observed sweat rate difference.
Baseline and post-exercise values indicated that males generated greater peak torque than females, as expected, based on a higher average muscle mass in males than in females. In our study, fluid loss due to exercise resulted in a significant muscle performance deficit that was not impacted by sex.
Although current literature is fairly inconclusive, results from many studies do suggest that dehydration negatively impacts muscular strength, power, and endurance [ 32 ]. However, there is relatively little research comparing potential dehydration-induced decline in muscle strength between men and women, and results of such studies vary.
The results of the current study do not necessarily support the notion that dehydration negatively impacts muscle strength, as the effects of dehydration were not isolated from the effects of exercise and muscle fatigue in this study. Interesting findings from previous work suggest that consumption of deep-ocean mineral water following a dehydrating exercise protocol improves aerobic performance and muscle strength [ 13 , 14 ].
In this more comprehensive study, we found that male and female participants demonstrated elevated rates of hydration recovery, and that peak torque of a leg extension may also be improved when fluid was replenished with deep-ocean mineral water compared to other fluids.
Therefore, improved acute hydration may be one factor by which deep-ocean mineral water improves exercise performance, as has been shown. Although we did not study the precise mechanism underlying enhanced fluid recovery with deep-ocean mineral water, it is likely that the unique mineral composition of deep-ocean mineral water contributes to this characteristic See Table 1 for a nutrient comparison of fluids.
A study by Hou et al. However, Kona Deep® contains far less Mg than the deep-ocean mineral water used in the Hou study, and therefore, we cannot necessarily predict that the modest difference in Mg between the three fluids in our study was a major contributor to the observed effects on muscle performance.
Additionally, we have no evidence to support a connection between Mg and hydration recovery. Another possible mineral contributor is boron.
Both Kona Deep® and the water used in the Hou study contain significant amounts of this trace mineral. Hou reports that boron attenuates the rise in plasma lactate, potentially delaying fatigue, and prevents Mg loss. As with Mg, however, we have no evidence to support a connection between boron and hydration recovery.
Interestingly, composition of the intake fluid impacts intestinal water flux more so than osmolality [ 34 ]. Carbohydrate-electrolyte sports drinks, such as Gatorade®, are proposed to increase intestinal water absorption due to the presence of glucose, which assists sodium transport into the intestinal cells via the sodium-glucose cotransporter, thereby influencing water flux by promoting an osmotic gradient [ 35 , 36 ].
However, we observed no greater acute hydration rate with Gatorade® compared to the other fluids. This may be due to the influence of gastric emptying rates, as fluids containing carbohydrates may decrease gastric emptying rate compared to non-carbohydrate-containing fluids [ 36 , 37 ].
Notably, slower gastric emptying rates may also decrease intestinal absorption rates [ 35 ], thereby slowing overall fluid uptake and assimilation into the body fluid compartments.
Several limitations of the study have been mentioned throughout the paper. We relied on the use of salivary osmolality as the sole marker of hydration throughout the study. Previous work shows that salivary osmolality is highly valuable for serial measures of hydration during intense physical activity in the heat [ 18 ].
More importantly, we needed multiple data points to best model instantaneous changes in osmolality throughout the dehydration and rehydration periods. Due to the continuous nature of the exercise protocol, serial urine collections were not practical for this study.
Some limitations do exist for the use of S osm as a marker of hydration, including an initial sharp drop in osmolality caused by oral rinse and variability between participants [ 3 , 15 , 17 , 18 , 19 ]. Furthermore, baseline, peak or the rate of increase in S osm across the 3 trials was similar for each participant, indicating S osm was an appropriate method for comparing rehydration fluids within each participant.
Participants were separated by sex based on secondary analysis of study parameters. Because the study was not powered for sex differences, analysis of peak torque would require further studies specifically powered for sex as a primary outcome.
Similarly, dietary restrictions were suggested and not strictly enforced and cannot be ruled out as a potential contributor to any sex differences. Finally, the American College of Sports Medicine ACSM recommends 1. In our study, participants replaced fluid lost in a ratio. During development of the protocol in pilot studies, participants were not able to ingest fluid amounts suggested by the ACSM recommendations.
In addition, participants did not urinate during rehydration, and all subjects completed the final saliva collection and muscle strength measurement at their full baseline body mass. Future studies will be designed to address these limitations as well as the underlying mechanisms by which deep-ocean mineral water elicited enhanced hydration effects, including the contribution of specific nutrients specific to deep-ocean mineral water.
Kona Deep® deep-ocean mineral water improved acute rehydration rate after a dehydrating exercise in both males and females, compared to spring water and Gatorade®. However, it remains unclear whether the hydration-enhancing effect of deep-ocean mineral water impacts performance recovery as demonstrated previously [ 13 , 14 , 15 ].
Future studies will be targeted at uncovering the mechanisms behind the hydration-enhancing properties of deep-ocean mineral water, further characterizing sex differences in these relationships, and correlating additional measures of hydration, such as serum osmolality, with that of S osm.
Bhave G, Neilson EG. Body fluid dynamics: back to the future. J Am Soc Nephrol. Article CAS PubMed PubMed Central Google Scholar. Bourque CW. Central mechanisms of osmosensation and systemic osmoregulation. Nat Rev Neurosci. Article CAS PubMed Google Scholar. Cheuvront SN, Carter R 3rd, Sawka MN.
Fluid balance and endurance exercise performance. Curr Sports Med Rep. Article PubMed Google Scholar. Shibasaki M, Wilson TE, Crandall CG. Neural control and mechanisms of eccrine sweating during heat stress and exercise.
J Appl Physiol Article Google Scholar. Lara B, Salinero JJ, Areces F, Ruiz-Vicente D, Gallo-Salazar C, Abian-Vicen J, Del Coso J. Check out another Bridge blog post on sleep's impact on athletic performance and the importance of good nutrition. References: 1. Sawka, Young, Cardarette, et al.
It's no secret that tactical professionals have weird schedules. So why do health professionals July 17, By Megan Fischer-Colbrie. Dehydration and Athletic Performance.
Athletes Need Water to Perform Most athletes know to drink water, but besides staying hydrated during practice, post-workout hydration is an important part of recovery. The Impact of Dehydration Hydrating properly can help an athlete sustain work capacity; in other words, athletes will be able to work harder if they drink more water.
Recap It can still be difficult to add in another health habit to a daily routine, if hydration seems out of sight, out of mind, make it more of a priority. About the Author. Related Posts.
September 26, Go ahead and refill your water bottle first. Not quite. Previously viewed as a state yes, no or almost , hydration might be better regarded as a process that includes an ongoing set of behaviors and biological functions.
Addressing hydration as a process makes sense because regular intake of fluids and excretion of urine, in and of themselves, confer benefits beyond maintaining water levels in the body Lafontan ; Perrier et al.
Drinking plenty of water is also an effective strategy for cutting weight! Humans have an inherent, critical need for water. It is the medium in which all of our metabolic reactions occur. Not only is regular fluid intake particularly plain water one of the easiest, cheapest health interventions ever; it may also be one of the keys to optimizing health and well-being over the long term Lang et al.
Good hydration habits appear to have an outsized positive impact on renal, cardiovascular and endocrine health and may even play an important role in addressing obesity Chang et al. Read also: Recommended Daily Water Intake. For example, in a study of people diagnosed with overweight or obesity, those who consumed milliliters of water just before each daily meal lost 2 kilograms more over the week study than did those on the same diet who did not imbibe before each meal.
TBW is in constant flux, with continual losses to respiration as water vapor and insensible sweat perspiration that happens before it is perceived , as well as intermittent losses to urine, feces and sensible perceived sweat. This output is about 2. Water needs vary from person to person.
For instance, people with obesity require more fluids than nonobese populations, owing to metabolic rate, body surface area and body weight Chang et al. For context, however, the National Academy of Medicine formerly the Institute of Medicine says that adequate fluid intakes for male and female adults are 3.
Worried about water weight? Don't be! Check out this blog on how to lose water weight effectively! However, the acute adjustments that allow the body to compensate can also set us up for longer-term trouble.
It can negatively affect mood, cognition, metabolism, and kidney and cardiac health, while possibly having implications for immune function and cancer prognosis Benton et al. More on consequences later.
To really grasp how dehydration and hypohydration affect the body, it helps to look more closely at the physical processes involved. As with real estate, one of the first things to consider is location, location, location. Most water in the body resides in two types of compartments: intracellular within the cells and extracellular outside the cells.
Intracellular fluid ICF refers to water inside cells, and extracellular fluid ECF refers to water outside of cells in the interstitium or plasma. Because cell membranes are permeable to fluid via aquaporins specialized water channels , fluid moves freely between the three compartments intracellular, intravascular and interstitial.
One cause of this is osmosis: In osmosis, water moves from areas of high fluid concentration to areas of low concentration in an attempt to balance the levels on both sides of the cell membrane.
This movement is driven, in part, by the quantity of solutes substances dissolved in the fluid in each compartment. Solutes cannot move through cell membranes, but fluid can. During osmosis, water moves from areas of lower solute concentration to areas of greater concentration, shifting the amount of water on each side of the membrane.
An area with a higher solute concentration cannot help but pull water into it, even if this creates other problems. When equilibrated, the three compartments—think of them as buckets—hold the appropriate amounts of fluid. However, when one bucket experiences a loss of water volume or an increase in solute concentration, water from another bucket is more likely to pour in to balance things out.
This difference between solute concentrations on the two sides of a semipermeable membrane is called an osmotic gradient , and it drives water flow between compartments. Water moving into or out of the ICF may cause cells to shrink or expand.
A little change in size is a small problem, but large shifts can trigger undesirable signaling cascades affecting metabolism, transport, hormone release, cell proliferation and programmed cell death Guelinckx et al. Cells get ticked when they shrink or swell.
Shrinkage of cells in the ICF is the consequence of chronic hypohydration, and you will soon see why it has been accused of health crimes. While the rules of osmosis may seem cut and dried fluid shifts until balance is achieved , the body is more complex than that: Certain parts of the body do a more important job than others, so they take priority when it comes to allocation of resources, including water.
However, adequate blood volume is critical to maintaining whole-body homeostasis. Lower blood volume and thicker blood means each organ system heart, lungs, kidneys, liver, etc. has to make do with less, making its job more difficult.
Thus, the body prioritizes the intravascular compartment containing plasma at the expense of other fluid compartments. One demonstration of this prioritization is that blood osmolality —the balance of water to dissolved substances—remains remarkably consistent in people with widely different levels of habitual water intake.
Maintenance of TBW depends not only on fluid ingestion but also on electrolyte concentration gradients in the fluid compartments. Electrolytes are electrically charged particles anions or cations from salts dissolved in water, and they are important for both rehydration fluid replacement and the capacity to hold onto a higher level of body water.
Sodium exerts the strongest influence because of its role as primary driver of volume in the extracellular compartments Leiper Fluid to form sweat is drawn from blood plasma, so exercise of longer duration poses a challenge to blood volume and viscosity.
Read also: Foods to Replenish Electrolytes :. Most diets in developed countries supply sufficient sodium to retain ingested water and, of note to athletes, to prevent exertional cramps.
If you have clients on sodium-restricted diets, they should initiate a discussion with their physician: In , the Institute of Medicine reported that there was a lack of conclusive scientific evidence of benefit or harm in reducing sodium consumption to previously recommended levels Kong et al.
This, in turn, drives blood volume and therefore blood pressure. This triggers the pituitary to release arginine vasopressin formerly known as antidiuretic hormone. AVP triggers reabsorption of water by the kidneys, making urine more concentrated.
It also results in constriction of blood vessels to maintain blood pressure and elicits feelings of thirst, inducing fluid intake. In conjunction, pressure-sensitive receptors in blood vessels called baroreceptors sense the decreased blood volume and respond by triggering the release of aldosterone, a corticosteroid.
When blood osmolality decreases or there is a large influx of water from the small intestine, AVP drops, thirst disappears, and the kidneys produce a greater volume of dilute urine.
While occasional mild hypohydration is not a problem, being chronically dehydrated may be a threat to long-term health and well-being. Low TBW keeps the RAAS in a constant state of activity, with high circulating levels of the hormone cortisol. In terms of exercise, fluid is important not just for aerobic performance but also for maintaining optimum muscle tissue.
Dehydration leads to increased production of urea a crystalline compound in urine , suggesting that water deprivation is accompanied by body tissue catabolism breakdown. Also check out: Monitoring Hydration Levels.
There is evidence that those with persistently low body water are at higher risk of serious chronic conditions, including type 2 diabetes, kidney disease and metabolic syndrome abdominal obesity, insulin resistance, hypertension and persistent inflammation.
AVP apparently alters liver glucose production and its breakdown of stored glycogen, while also impairing insulin secretion and insulin sensitivity Qian In people diagnosed with type 2 diabetes, low TBW deteriorates glucose regulation. Diabetes is already a challenge to TBW because excess glucose in the blood acts as an osmolyte, pulling water from cells to counteract the higher osmotic pressure in the ECF.
The kidney glucose transporters become saturated, so glucose is lost in the urine, pulling excess water with it. Thus, the water never gets to the ICF, where the thirst was triggered—hence, the diabetes symptoms of excessive thirst triggered by cellular dehydration and large volumes of urine following glucose loss in the urine.
Although it may seem counterintuitive given the excessive urine production , restricting water will only exacerbate the problem for people with diabetes. Blood glucose clearly needs to be controlled, but optimal hydration will help the body better manage the condition overall. A broad range of other diseases are also associated with markers of hypohydration: heart failure, vascular dementia, cognitive impairment, inflammatory bowel disease, cancer and premature mortality Lang et al.
Obviously, many of these illnesses are multifactorial, and association is not causation. These recommendations are lower than those from the National Academy of Medicine. For adults, EFSA recommends water intakes of 2. Many factors affect how quickly the body takes in fluids consumed in food and beverages.
Water absorption, which occurs mainly in the small intestine, is important for everyone but may be particularly of interest to athletes wondering how much and what to drink before, during and after various levels of energy expenditure.
Whether we absorb the water from fluids we consume depends on our gastric emptying rate, or how fast fluid leaves the stomach. Following are some factors to consider when seeking to speed up gastric emptying rate and get fluids to the body parts that need them most.
In general, the greater the volume of fluid in the stomach, the faster it exits. This is true up to about mL, at which point the rate may level off. Personal tolerance varies, of course. Interestingly, refilling the stomach regularly with a larger volume, rather than drinking slowly and continually, will enhance gastric emptying Leiper ; however, drinking a large volume in a short time right after working out is not recommended.
Beverage temperature, contrary to a popular myth, does not affect water uptake. Plain water is emptied from the stomach and absorbed in the intestine faster than fluids containing electrolytes or calories.
Here are a few types of beverages and their notable characteristics:. FRUIT JUICE AND SOFT DRINKS. Solute concentration in fluids osmolality is measured in milliosmoles per kilograms.
The problem with hypertonic beverages, which include fruit juice and soft drinks, is that they draw water out of the body-water pool into the intestine to make them isotonic; this delays absorption of their water content and makes them ineffective for rapid rehydration, especially during or following competition Leiper SPORTS DRINKS.
Carbohydrate-electrolyte solutions aka sports drinks that have a carbohydrate concentration of 2. However, sports drinks can have their problems.
Also, many store-bought versions contain fructose, which has been shown to enhance carbohydrate oxidation at low-to-moderate exercise intensities but can be difficult for some people to digest Jeukendrup Incidentally, fructose is found in fruit juices and many other sweetened beverages, too.
If someone gets gassy or uncomfortable after drinking a commercial sports drink, fructose may be the culprit. For context, a Starbucks ounce black coffee has about mg, a double espresso about mg. When exercise will last longer than 2 hours or take place in high heat, exercisers should arrive optimally hydrated—neither hyperhydrated with an excess of TBW nor hypohydrated at a deficit.
This is particularly important if fluid loss from sweat will be high in which case sodium losses via sweat will probably also be high.
Beginning an endurance event hypohydrated compromises performance: The water deficit increases cardiovascular strain, raises heart rate and rating of perceived exertion for the same relative effort, and amplifies the thirst sensation. High temperatures increase the degree of impairment and discomfort.
Anaerobic endurance, muscle strength and power all decrease, as well. Further, such dehydration can induce plasma hyperosmolality, which increases heat storage by delaying and decreasing sweating in an attempt to conserve water Paull et al. Overhydration does not enhance performance, either. Hyperhydration higher than optimal TBW does not improve aerobic or anaerobic performance and can, at extremes, be fatal McDermott et al.
If blood levels of sodium become hypotonic too dilute , osmotic pressure in the extracellular compartments decreases. This becomes particularly dangerous in the brain because cell swelling there will lead to increased intracranial pressure, a dangerous condition called cerebral encephalopathy.
Nutrition American Fitness Magazine. Originally published Consisteny Consistent hydration for sustained performance spring issue of the Consitent Fitness Anti-oxidation benefits. News cor Consistent hydration for sustained performance, hydratin old H2O. Okay, so the photo was a bit of a spoiler. Even for Nutrition Coaches who have always valued good hydration in their own self-care regimen, many of the associated complexities may come as a surprise, as they are grounded in research that is new or has been recently updated.
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