Science for the Endurance Athlete: Are Slushies the key to better performance for endurance athletes in hot weather?

Resident Exercise Science geek Tim Curry here with a study I ran across that may make you run to your local gas station for a  slushie before your next ride on a hot day…

A new use (besides causing brain freezes) for the common slushie has been found by researchers in Australia.  A brand new study that was published in the most recent issue of the American College of Sports Medicines Journal: Medicine & Science in Sports & Exercise looked at the effects of drinking an ice slurry (aka a slushie) on endurance running in hot weather (hot = ~93 degrees Fahrenheit).  The runners in the study drank 7.5 grams of either a slushie (not sure quit yet how many fluid oz. this is…) or cold water per kg of body weight 30 minutes before running at their ventilitory threshold (VT).  SIDE NOTE: VT is almost equivalent to a persons Lactate Threshold which is the point at which the body cannot clear lactic acid out of the blood as quickly as it is produced; basically you can only exercise at this point for a limited amount of time before your body will stop you from continuing.  In the end it was found that the runners ran for 19% longer (which was an average of 10 min. longer in the study) when they drank the slushie vs. the cold water.  This massive increase in running time with the slushie was attributed to the lower starting core temperature and higher end core temperature of the runners.  Cooling the core temperature of an athlete is not a new concept (think of the ice vests that riders used in during the TT warm ups in the Tour de France) and has been shown to be effective.  The concept behind this study is that it is more efficient and effective to cool the body from the inside-out not the outside-in.  On this point the authors were correct and found that a slushie is the most effective means of cooling for the following reason.  Warning Science Content:  Slushies are more effective due to the fact that it takes more energy, in the form of heat in our body’s case, to make water changes states from ice to water then it does to simply heat up cold water.  Ipso facto, slushies, because they are mostly ice, cool down the body better than cold water does. So what does this mean for us endurance athletes?

Basically, the results of this study point out a simple, and obvious, fact: cooling the body from the inside-out is very effective and taking advantage of some the chemical properties of matter (see science content above) helps out too.  The bottom line is this, if you are an endurance athlete who is going out on a ride in the summer, or whenever it is hot,  try drinking a slushie before you head out (30-60 min. before).  You should find out, as the study shows, that you can last longer at a higher pace due to your lower starting core temperature.  This means that during that killer climb in your ride you may leave your riding partners or competitiors in the dust because you can last longer than they can thanks to your lower starting core tempurature.  Who knows, in a race you may just place higher in a competition because of the lower core temperature… Who knew the humble slushie could do so much for endurance athletes?

-Tim Curry

P.S. If you have and questions just post them in the comment area and i will try to address them ASAP.

Information source:

Siegel, R., Mate, J., Brearley, M.B., Watson, G., Nosaka, K., & Laursen, P.B. (2010). Ice slurry ingestion increases core tempurature capacity and running time in heat.  Medicine & Science in Sports & Exercise, 42(4), 717-725.