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Wood, C.L., Burke, L.M., (2004) The effect of drink bottle flow rate on fluid consumption and fluid balance in elite level athletes. Australian Institute of Sport, Canberra, Australia (incomplete research, unpublished)

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Introduction

Maintaining body water balance is important for preventing reductions in sporting performance both physically and mentally. During an intensive game or training session, particularly in hot, humid conditions, sweat loss can be excessive. Replacement of this sweat loss is essential to keep the body in a well-hydrated state. When sweat losses are high, athletes may find it difficult to replace this loss. Accessing fluids from water bottles may be a limiting factor in the replacement of fluids.

We know that fluid consumption can be affected by several factors, and thirst is not necessarily the main one. The flavor of the fluid has been shown to enhance consumption (Wilmore et al., 1998). The availability of fluid may also be a factor. This study was to investigate what effect the bottle flow rate may have on the quantity of fluid an athlete consumes. The reason that flow rate may influence consumption is that a larger nozzle/ mouthpiece may allow a greater rate of fluid release into the athlete's mouth. This is particularly relevant in sports in which the time available for rehydration is limited (only short breaks in play).

Team sports that have a limited number of breaks in play and limited time during breaks to drink may be particularly affected. There is currently no research that looks at this factor and its effect on fluid volume consumption during exercise.

The first hypothesis is that a larger nozzle/ mouthpiece and hence greater flow rate will influence fluid consumption of athletes by allowing a greater rate of fluid release into the athlete's mouth while drinking. The second aspect of this study was to determine if this greater flow rate and increased fluid consumption would lead to more adequately matched fluid intake with fluid losses during exercise, meaning improved fluid balance.

Methods

Two sets of trials were conducted. Trial one was done with the Australian Institute of Sport (AIS) men's and women's basketball squad, and the second trial with the Australian Capital Territory Academy of Sport (ACTAS) netball squad. All athletes tested are developmental athletes: ten female basketball, three male basketball and six female netball athletes completed the study.

A randomized crossover design, with two conditions (high and low flow rate) was conducted to determine if a greater flow rate was to enhance fluid intake over a 1.5-2 hour training session. A 1-litre drink bottle was used and manipulated to create two different nozzle sizes. This was achieved by drilling a hole in the center part of the nozzle piece to increase the flow rate.

Athletes were randomly assigned to either the low flow rate or high flow rate group, ensuring that court position was matched in each group. Three sessions were monitored with all subjects, the first a familiarization trial using the regular (low flow) bottle first, then the subjects were assigned to one of the study groups, and repeated with the other bottle type. Comparing the low flow familiarization trial and the trial repeat with the same bottle allowed for an internal control to ensure each individual drank the same volume on two separate occasions with the low flow rate bottle.

Heart rate monitors were used to compare the intensity of each of the training sessions. Plain tap water was used for consumption in all trials.

Hydration status was monitored by body weight changes (towel dried, minimal clothing) over the training session, and fluid intake was measured by weighing the drink bottles to determine changes in intake during each different trial. Athletes were closely monitored to ensure that they drank from the same designated bottle.

The temperature and humidity were measured on each of the test days to monitor environmental conditions.

Results

Flow Rate Analysis

The flow rate of the original and manipulated nozzle openings was tested by measuring the rate the water flowed out of the bottle when tipped upside down with no pressure applied to the sides of the bottle. A one-liter bottle with a regular nozzle opening allowed one liter of water to pour through in 26 seconds giving a flow rate of 2.3 l/min, the one liter bottle with the large nozzle opening allowed one liter of water to pour through in 14 seconds giving a flow rate of 4.3 L/min. The flow rate was almost doubled with the manipulated nozzle opening. The original nozzle size is referred to as the low flow rate (LFR) and the manipulated nozzle is referred to as the higher flow rate bottle (HFR).

Exercise Trail Results

Discussion

Trial one with the AIS basketball athletes showed no difference between the greater flow rate bottle and the regular bottle. Most of the athletes closely matched fluid intake with their sweat losses to maintain body weight over the training session.

The AIS athletes of the first trial were very well educated in hydration strategies and keeping fluid intake to a level as to not compromise hydration status. Maintaining a good hydration status over the training session is desirable, and we believe that the high education level of AIS athletes on maintaining hydration during training resulted in no difference in fluid balance between the groups.

The second trial was conducted on a 'less well educated group' in the thought that we may see a difference in fluid balance comparing the two groups. No difference in fluid balance was also seen in the second (netball) group, they managed to match their fluid intake well with their sweat losses.

The duration of the netball training session was shorter than the trial one participants, and heart rate analysis showed that the intensity was also well below that of the basketball sessions. Both trials were conducted in fairly cool conditions meaning a lower sweat rate, and greater ease in matching fluid intake. If the temperature was hotter or the intensity of the sessions were greater there may have been a greater difference seen.

These findings also create some discussion around how an athlete monitors and replenishes their own fluid intake. An athlete may drink the desired amount of fluid until they have satisfied their thirst, or may habitually just drink a certain amount, or take a certain amount of sips. If the flow rate is greater coming from the bottle in the third situation, then the athlete may be able to get more fluid into the mouth without even realizing it. Considering that this study found that a similar amount of fluid was ingested, irrespective of the flow rate, would indicate that the athlete is good at monitoring how much fluid they are ingesting, and adjusting accordingly.

Providing water bottles during training and competition helps to enhance hydration during an exercise session. This increase in assistance may be more important than any difference or increase in the flow rate of a drink bottle.

References

• Wilmore, J.H., Morton, A.R., Gilbey, H.J., Wood, R.J., 'The role of taste preference on fluid intake during and after 90-minutes of running at 60% of VO_2max in the heat', Medicine and Science in Sports and Exercise, Vol 30(4) p587-595, 1998. 

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Related Pages

• Full list of research papers by Clare Wood
• Hydration and Athletes
• Sport & Science Research Guide