For National Football League athletes, sitting out a game due to freezing, dangerously cold weather is not an option.
In fact, the NFL hasn't postponed or canceled a football game due to low temperatures since 1933.
The Green Bay Packers took on the Dallas Cowboys at Lambeau Field in the 1967 National Football League Championship Game, also known as the Ice Bowl, in temperatures of minus 13 degrees Fahrenheit with a wind chill of nearly minus 50 F.
It turns out that the fans don't mind, either.
In December 2017, devoted supporters packed New Era Field to see the Buffalo Bills defeat the Indianapolis Colts in whiteout conditions.
A post shared by Aj Mussachio (@buffalo_poi_guy) on Dec 10, 2017 at 10:31am PST
The game must go on, so football players have to do what they can in order to preserve their body's warmth on the field.
"Football players are not immune to the effects of cold that impact everyone, [including] lowering your body temperature and local exposure to freezing cold conditions in terms of its effect on skin and soft tissue that are exposed," said Dr. Samuel Taylor, sports medicine surgeon at the Hospital for Special Surgery.
"It's important that players have the appropriate equipment to keep them warm and to protect them from the elements as best as they can," said Taylor, who's also an associate team physician for the New York Giants.
Here are five ways NFL players keep warm on the field when playing in freezing weather.
1. Mental preparation
Getting started on the field in below-freezing conditions is no easy feat for NFL players.
"It's not that you don't want to be out there; it's just that you don't want to feel that cold," Terence Garvin, linebacker for the Seattle Seahawks, told AccuWeather.
For three-time Super Bowl Champion and former New England Patriot Troy Brown, playing in the cold and snow was mind over matter.
In near blizzard conditions, Buffalo Bills quarterback Trent Edwards (5) scrambles for 12 yards and a first down in the third quarter of an NFL football game against the Cleveland Browns on Sunday, Dec. 16, 2007. (AP Photo/Ron Schwane)
Preparing mentally and physically as much as possible prior to each game was Brown's key strategy, which included training himself to get used to the cold football stinging his fingers as it made contact with his hand or adapting to the loss of feeling in his toes.
Getting past that part made playing the game easier, he said.
"I usually didn't even think about how cold it was until I was back in the building getting ready to go home and started getting feeling back in my fingers," Brown told AccuWeather.
"It hurt to warm back up, and that's usually when I realized how cold I had actually gotten," he added.
2. Hand warmers
Football players use hand warmers just about anywhere they can think of, including the tops of their feet in their cleats or inside of their helmets.
They provide some relief from the cold, but they won't last the entire game.
Some players who choose not to wear long sleeves slather Vaseline on their arms and faces to avoid shivering in the cold.
"The idea [is] that it closes the pores a little bit and gives you a little bit more protection from the elements," Taylor said.
Officials frown upon the use of petroleum jelly because it makes players more slippery to opponents. They're permitted to use it in extreme cold conditions, however, as long as they don't apply too much product.
4. Layering up
Some players add layers underneath their uniforms to provide an additional barrier against the cold.
New England Patriots quarterback Tom Brady has been known to don a scuba suit as insulation and protection from biting cold winds.
"While a scuba suit works really well, it wasn't an option for me, because in the positions that I played, I had to move around a lot on the field and I needed the freedom and flexibility to do that," Brown said.
Bundling up while on the sideline also helps.
5. Heated benches
"We have heated benches and heated foot pads are underneath where the players' feet go while they're sitting in order to help keep them warm," said Taylor.
Benches also include helmet warmers, which are perfect for heating up an ice-cold helmet before getting back in the game.
Players have to be careful not to bask in the warmth for too long, because it will make it harder to get back out onto the freezing field, said Brown.