Dangerous Heat & Summer Sports

Whether it’s a summer league or preparation for a competitive fall season, sports in the summer heat bring the risk of heat cramps, heat exhaustion, and heat stroke. Between 1997 and 2006, 75% of exertional heat-related injuries were associated with exercising or participating in a sport. The effect of heat and humidity combined, or heat index, is used by NOAA to determine how quickly heat-related illness can set in. As climate change increases the number of days when the heat index climbs toward the dangerous level, managing the heat during exercise will become more vital.

When a location hits the Extreme Caution category (90°+), a healthy individual can start experiencing heat cramps. Nationwide, there are already many places that regularly spend much of their summer in this zone. The next category is Danger (105°+), and that’s when the body starts to go into heat exhaustion. Overall, there are relatively few Danger days across the U.S., but that is changing with our changing climate. And as the planet continues to warm from increasing greenhouse gases, the number of Danger days is expected to rise - increasing the threat of heat-related illness.

When the body’s core and brain temperatures get too high, blood flow and muscle strength both decrease. During exercise, body heat production is 15 to 20 times greater than at rest, and getting rid of this heat is critical to avoiding illness. While active, up to 90% of body heat loss comes by evaporation of sweat, compared to only 20% at rest. But heat loss by sweating can be dramatically impaired at relative humidity above 60%. And once dehydration sets in, the body cannot produce sweat to cool itself, which is an initial step toward heat illness.