Johanna O'Connell and Steven Cady are both avid runners, but the higher the temperature climbs, the harder it is for them to keep going.
"You just really start to feel sluggish. You're sweating so much that you really get dehydrated pretty quickly," said Johanna.
Now they are wearable ice packs that are supposed to cool down the body temperature.
Mary Jo Warner is a spokeswoman for Cool Palms, which makes the BEX Runner.
"As your core temperature goes up, your performance goes down. So a lot of people are not able to run in the heat for very long. This enables you to run further, longer, and have a better training session," said Warner.
She says the device works by cooling the blood vessels in the palm, which is then circulated through the rest of the body.
But some doctors aren't sold, including Emergency Room physician Dr. Eric Glasser .
"It may keep you cooler for a very short period of time. It certainly will not prevent things like heat stroke, heat exhaustion, the heat related illnesses that we see in the emergency department,"
He says in theory, devices like the BEX Runner could work, but there's no scientific data backing it up.
"The small amount of blood that is cooled and sent back downstream, by the time it gets to the rest of the body, it's not going to be much cooler than the rest of the body temperature, " he said.
Steven Cady has been using the device for a few weeks. He's noticed a difference.
"It makes you feel more comfortable. You don't really notice the conditions as much. You feel much fresher as you get to a certain distance, when you were tired before, you're like, oh, this is great," said Cady.
The owner of Cool Palms, which makes the BEX Runner, says he's not surprised that doctors are skeptical because the concept is so new. However, he points to one study in the journal Medicine and Science in Sports and Exercise, which did find that weight lifters who cooled their palms between sets experienced less fatigue and were able to do more reps.
For more information, go to the BEX Runner website.