Sweatlabs: How Does Pre-Cooling Affect 5km Running Performance? 

• Athletes receiving any of the three cooling strategies (head cooling, ice-ingestion, and cooling vest) had significant performance increases compared to runners using the control strategy (decrease in time of 1.3–1.8 minutes, compared to the control times of 22–30 minutes). 
• No differences in 5km performance were found amongst the three different pre-cooling strategies. 
• Peak core temperatures for the cooled runners were 0.3°–0.5°C lower than the control-group runners. 
• The head-cooling strategy saw the least amount of core temperature reduction, even though 5km performance was similar to the other strategies. 

14 active young men, moderately trained (aerobic exercise at least 3 times/week), each completed 4 running time trials (5-km on a 400m track) across 4 weeks. Each runner experienced each strategy and the control in random order.  

Temperature was 32°–34°C wet-bulb globe temperature, with 60% relative humidity. This translates to approximately 40°C/104°F air temperature and is considered a Very High to Extreme condition for exercise.  

Before each time trial there was 20 minutes of pre-cooling. Either: 

• Wearing a gel-based head-cooling cap (pre-cooled to 0°C) 
• Ingesting crushed ice (7.5/grams per kg of body weight) 
• Wearing an ice cooling vest over the torso 

The control runners sat in the shade for 20 minutes and were allowed to ingest warm water up to a volume of 7.5/grams per kg of body weight. 

During the time trial, runners in the three pre-cooling categories received 100 mL of crushed ice every 5 minutes. Runners in the control group could drink warm water at the same quantity and frequency. 

During the time trial, runners were self-paced with no external indications of their pace or time. 

Each runner’s core temperature was measured with a CORE sensor attached to a chest strap. 

• The test supports prior studies showing the performance benefits of cooling strategies before and during endurance exercise in hot and humid conditions. 
• The failure to find a performance difference amongst the three pre-cooling strategies supports our belief that cooling is a very individualized endeavor. The ideal cooling strategy may depend on the duration and intensity of the event, the relative humidity of the air,athlete fitness level and heat adaptation level, and individual reactions to various strategies.    
• In this study, the constant per-cooling strategy (ingesting ice while running) may have cancelled out some of the differences among the pre-cooling strategies. It is unknown how much of the performance gain could be attributed to the pre- versus per-cooling. 
• Runners wearing the head-cooling cap had a higher core temperature but a similar performance benefit as the other strategies. This does not surprise us, knowing the de-motivating effect of overheating (a hot brain tries to slow down the body). Our SweatLabs team recalls a conversation with Daniela Ryf where she spoke of the importance of keeping her temples cool during her 5 Ironman World Championship wins – that cooling kept her brain sharp and let her make good decisions. 

Pre-cooling and per-cooling effectiveness are dependent on many variables. We would be interested in seeing the effectiveness of different protocols in various situations. The CORE sensor’s convenience, low cost, and test/retest reliability make it an ideal tool for studies of this nature.  

Of particular interest to athletes and coaches we’ve heard from: 

• Is there a difference amongst pre-cooling strategies when little-to-no per-cooling is available? 
• In longer events, does pre-cooling act like a heat sink, delaying the onset of elevated core temperatures? 
• In very high-intensity events, does a cooling vest tighten the intercostal muscles and hinder breathing (by preventing full chest expansion). 
• Are some pre-cooling strategies more effective than others in hot and dry climatic conditions? 
• What is the shortest event duration where pre-cooling gives a performance benefit? 
• What is the lowest temperature/humidity where pre-cooling gives a performance benefit?