Logo Largest

Q: How does RRWP estimate group water needs, exactly?

A: RRWP uses a patent-pending algorithm known as H2Q Technology™ to accurately estimate the need of the ‘weighted average’ runner, which is determined from a normal distribution of body sizes and marathon finishing times estimated or obtained from more than 3 million runners.  Body weights and finishing times are then binned and weighted by their frequency distributions.  A range of possible environmental temperatures is included in each bin.  A proprietary algorithm is used which requires the user to input race distance, number of runners, and air temperature to arrive at total water needs for the race.  On the basis of the central limit theorem, RRWP provisions are enough to accurately estimate the water loss needs of everyone participating so long as the sample mean is representative (heterogeneous, sufficiently large and normally distributed).

Q: Can RRWP be used to estimate “individual” exercise water needs?

A: RRWP should NOT be used to estimate water needs for individuals.  The equation provides what the ‘weighted average person’ will need, thus it will in many cases over-estimate or under-estimate individual needs despite accurately estimating enough water to cover the water losses of everyone participating.  If knowledge of individual water loss needs are desired, H2Q Technology™ should be used in conjunction with measurements of air temperature and “individual” energy expenditure [H2Q].

Q: What is the range of environments covered by RRWP?

A: RRWP was designed for air temperatures anticipated during the most popular months for road races (April – October).  The optimum ‘domain of validity’ for RRWP is 10 to 35ºC (50 to 95ºF).  However, RRWP will allow users to input air temperatures ranging from 4 to 40ºC (39 to 104ºF).  The air temperature used should be the average forecasted for the duration of the race.

Q:  Why doesn’t RRWP consider relative humidity?

A:  When it comes to evaporative heat loss from sweating, it is the absolute humidity that matters (i.e., the air water vapor pressure, Pa).  RRWP covers a range of absolute humidity anticipated based on the times of year, latitude locations, and times of day when races are conducted.  Although RRWP might underestimate sweating during periods of combined high air temperatures and high absolute humidity, it is recommended that road races be canceled under these extreme conditions.  Therefore, RRWP should provide an adequate solution for most race circumstances without the need for any relative humidity input.

Q: Why doesn’t RRWP use the Wet Bulb Globe Temperature (WBGT) Index?

A:  The WBGT was not used for several reasons.  For example, the WBGT cannot be easily forecasted, and water planning that includes weather parameters as an input must be estimated in advance of any race.  The WBGT is also not yet widely adopted in practice by race or medical directors.  The RRWP development goal was to use the fewest inputs possible for ease and acceptability.  Air temperature is commonly forecasted and is available ubiquitously (apps, radio, television, internet).  Most importantly, air temperature is all that is needed for high accuracy.

Q: How does RRWP estimate how much water is spilled or used for dowsing?

A: RRWP water needs estimates are synonymous with runner sweat losses.  RRWP provisions are enough to cover the sweat losses of all runners, assuming that all runners drink to replace sweat losses (1:1).  Some runners may drink more or less than this amount, but RRWP assures that the right amount is placed on the course to replace sweat losses.  RRWP also has a 10% spillage factor built into it, but this is an estimate for which there are no quantitative data.  Therefore, calculations should be considered as a valid starting point for water planning and adjusted in accordance with the history of actual water usage on the course.

Q: How accurate is RRWP?

A: The accuracy of RRWP for predicting group water needs can be gleaned from a validation study that has been accepted for 2019 publication in the journal Medicine & Science in Sports & Exercise (https://www.ncbi.nlm.nih.gov/pubmed/30531484).  The mean absolute difference (MAD) between predicted and measured sweating rates from 12 published studies was 0.120 L/h, or approximately 4 fluid ounces per hour.  When predicted race water needs were compared to water usage at the 2017 Boston Marathon, the study conclusion was that RRWP error was sufficiently small to provide event organizers with a quantitative way to narrow the uncertainties of water planning related to changes in weather, participant numbers, and race distance.

Q: Does the caliber of runner affect the prediction accuracy?

A: In principal it does not matter the “general” caliber of runner as long as the race group size is large enough.  RRWP was developed using a broad range of running speeds.  However, if the group is small or the entire group runs faster or slower than the development range on average, then RRWP accuracy could decline.  Fortunately, large groups are the norm for road races (e.g., ≥ 100 people) and running speed should vary enough among any group of ranging ability for RRWP to work well.

Q: How does RRWP determine the number of cups needed?

A: RRWP assumes that 4 fluid ounces will be poured into each cup.  It takes 32 cups to empty one gallon of fluid.  The rest is simple arithmetic.

Q: Why does RRWP assume that water should be distributed equally among fluid stations?

A: There are different strategies for supplying water on a race course which depend on logistics, course design, and the number of registered runners (to name a few).  RRWP simply divides evenly the total amount of water planned across the number of water stations entered.  It is a suggestion aimed at saving the water planner a calculation (similar to cup numbers), but also reduces the potential for over- or under-supplying runners at any one station.  The RRWP calculator also provides an estimate of the necessary number of fluid stations for comparison to those planned.  For more detailed information concerning optimal distribution of water stations in road racing please see supporting science (Cheuvront and Sollanek, 2020) at Road Race Water Planner on this website.

Q: Do I really ‘need’ RRWP as a race director?

A: Aid stations are an essential part of any road race, but there is presently no scientifically defensible way of accurately planning water needs for large groups in sport the way there is in the military (https://www.army.mil/article/136391).  RRWP was developed to narrow race and medical director uncertainties about water planning that relate to changes in weather, participant numbers, and race distance.  RRWP can improve pre-event planning, race-day preparedness, and is consistent with growing eco-friendly race initiatives.  Think of RRWP as a free supplemental insurance policy that can help reduce the risks, waste and costs associated with executing all of your road races.