Hundreds of professional cyclists will pack Knoxville's streets this weekend as the USA Cycling Pro Road National Championship returns for the second year.

They've been training for this race for months.

In a hot place like Knoxville in the summer, training involves more than just riding their bikes.

"They're constantly they're drinking all that water all the time, and then it goes beyond water," said Gary Chambers, co-owner of the Bike Zoo in West Knoxville. "Of course if you're really doing heavy duty exercise, you know the other problem is you're losing a lot of salt."

Chambers said hydration is key.

Cyclists racing at this high of a professional level are ready to ride in any weather condition.

That's thanks in large part to the gear that's designed to keep them cool.

"The back [of the jersey] is an almost mesh-like material," said Chambers. "So if you think about air flowing through and past you, and again we're trying to pull the sweat off your skin onto the material. Then the material is light and airy enough hopefully that it starts to evaporate."

Helmets are also now designed with lots of ventilation for air to keep your head cool, while keeping you safe.

Thousands of spectators are expected to attend the race this weekend, and it's just as important for them to stay hydrated and cool, too.

"Keep that water bottle with you, keep it full and keep drinking and it'll be a whole lot more fun," said Chambers."

The first event of the weekend is on Thursday in Oak ridge, the criterium that circles through downtown Knoxville is on Friday and the 100+ mile road race will take place on Sunday.

The event is free all weekend, just make sure you bring water along.

The race routes and best places to watch the bikes can be found here.

MORE: USA Cycling Nationals returns to East Tennessee