Nutrition Nerd: Ice Slurry Ingestion Prior to Running in Hot Environments
Written by Tanya, Nutrition Nerd: Is the temperature rising where you live? In Virginia it seems like we went straight from Fall to Summer, skipping over both Winter and Spring this year. Over the past month we have experienced multiple days of 80+°F and even some days in the 90s! As we all know, the rising temperatures can negatively influence our training. Running becomes more difficult as our body struggles to adapt to the changing environment. Pace slows, rate of perceived exertion (RPE) increases, the threat of heat stroke/heat illness becomes an issue, and the thought of hitchhiking a ride home from strangers while out on a long run tends to seem like a good idea. Well maybe that’s just me on the last one. I’m sure no one else has ever had that idea pop in to their minds before, right?? So as the summer weather starts to appear the next few weeks, what can we do from a nutrition standpoint to help keep the temperature from cutting our workouts short?
One way to help increase exercise time to exhaustion in the heat is known as “Pre-cooling”. Traditionally pre-cooling included full-body immersion in cold water or wearing “ice jackets” prior to running in hot/humid environments. The reason for this is because in hot and/or humid conditions the temperature and vapor gradients between the skin and air are not conducive to loss of heat. Thus, body temperature increases and becomes a performance limiting factor. Pre-cooling through these methods have been shown to reduce resting body temperature and therefore increase exercise time by delaying rise in core body temperature. However, submerging ourselves in a cold bath or using an ice jacket are not all that practical.
Newer research has examined if ingestion of an ice slurry (aka, crushed ice similar to a sno-cone or shaved ice in consistency) prior to running in hot/humid environments is an effective and more feasible method of pre-cooling. Compared to ingestion of cold water (39°F) prior to exercise, intake of the same amount (7.5 g per kg body weight) of an ice slurry (30°F) resulted in longer running time (an average of 50.2 minutes vs. 40.7 min) in a hot environment (~94ºF). Heart rate and sweat rate were similar between conditions, but during the ice slurry condition core body temperature was lower prior to the start of exercise and higher at exhaustion. In addition, ratings of thermal sensation (aka – how much is the heat a factor right now) and perceived exertion were lower in the ice slurry condition. (abstract) This study has been repeated using flavored water and ice slurries with the same results (abstract).
So it has been shown that ice slurry consumption is a better pre-cooling strategy than consumption of cold water, but is it as good as whole body immersion in cold water? YUP! Seems to elicit similar effects. The research design essentially repeated the above study, but this time added in a cold water immersion trial and used warm water as the control. The results showed that running time was longer following cold water immersion and ice slurry ingestion compared with the control condition, but no statistically significant differences emerged between immersion and ice slurry conditions. This shows that intake of an ice slurry may be comparable to the previously studied pre-cooling strategy of cold water immersion for exercise in hot environments (abstract).
Try It At Home:
The protocol for each of these studies had subjects consume 7.5 grams per kilogram of body weight of an ice slurry 30 minutes prior to running. To determine how much this would be for you, divide you weight in pounds by 2.2 to obtain your weight in kilograms, and then multiply by 7.5 to obtain the number of grams of an ice slurry you should consume.
I recommend using the “crushed ice” button on your freezer’s ice dispenser if you have that option, adding a small amount of water, and mixing in some Gatorade or Crystal Light powder for some flavor. If you do not have crushed ice available, then possibly put ice and some Gatorade or a small amount of water in to your blender to help turn it in to more of an ice drink/food instead of straight ice cubes.
I have not come across studies looking at the effects of ice slurry consumption during exercise as opposed to cool or warm water, but any benefit it may have will probably be thwarted by practicality. I.e. – It’s going to melt if you take it along with you!
Consumption of an ice slurry is not a substitute for proper training, heat acclimatization or fluid intake for exercising during the summer months. Training in the heat results in acclimatization which lowers resting body temperature and provides cardiovascular adaptations that aid heat loss. Proper hydration via fluid intake can attenuate the loss of plasma volume that would otherwise reduce blood flow to the skin and thereby compromise dissipation of heat. It is also important to pay attention to physiological cues that would normally cause you to reduce exercise intensity and/or duration in the hot weather. Knowing that ice slurries have been shown to increase high-intensity exercise in the heat could result in a placebo-effect in which we keep working beyond our limits simply because we are expecting the nutrition intervention to work. In the heat, this can result in a dangerous situation if we do not listen to our bodies and stop exercising if needed. So be smart and stay safe!
Have you ever tried any of these pre-cooling methods? Which ones? What did you think? Would you be willing to try an ice slurry pre-cooling strategy? And most importantly – what is your favorite shaved ice flavor? There is one called “Tiger’s Blood” I once had and loved…but I have no clue what flavors went in to make it!
(Tanya is a Registered Dietitian (RD) and is pursuing her PhD in Nutrition and Exercise Science at Virginia Tech. After graduating with her Bachelor’s in Dietetics, Tanya completed an American Dietetic Association (ADA) approved Dietetic Internship through the University of Houston. She has completed many road races from 5k to 25k. Follow her on Twitter @nutritionnerd and at her personal blog Dine, Dash & Deadlift.)