When do marathon swimmers slow down to fuel up mid-race?

RIO DE JANEIRO — Marathon swimming is a two-hour race on the open water where there are all kinds of variables from waves to water temperatures. But one of the biggest tactical decisions for a swimmer is when to fuel up during the race.

If you watched the women’s 10-kilometer race on Monday, won by Sharon van Rouwendaal of the Netherlands, you might have noticed little boats surrounding the pack with cups on the end of sticks extended out for the swimmers to grab. Inside those cups are a variety of calories and electrolytes and whatever else is helpful to get through a brutal race.

Think of it like a pit stop in auto racing: A swimmer needs to decide strategically when is best to slow down, at least for a few seconds, to drink something and perhaps give them an added burst of energy.

“I was trying to drink as much as possible because you’re swimming two hours in the sun,” van Rouwendaal said. “It’s sort of like Powerade. It’s a white powder called Prolong from Herbalife, and it keeps me going just a bit. It has a bit of sugar in it.”

There are several variables that play into the decision. One is that the handoff probably should take place in calm waters, given the degree of difficulty for a swimmer to grab a small cup and get it all down while on the move. The other major issue is that putting something in your stomach while you’re swimming amidst ocean waves can cause nausea during the race.

“I never was seasick but after you take your feed and go into some waves sometimes it doesn’t sit well,” said American Haley Anderson, who finished fifth after winning the silver in 2012. “I fed the first two laps and you kind of go into the waves after that so sometimes it doesn’t sit well then.”

Australian Chelsea Lea Gubecka signaled to her crew that she wanted to feed early in the race and said it was a clean handoff that didn’t cost her any time. Still, it’s an interesting debate: Do you do it when you’re toward the front and perhaps slip back in the pack, or do you wait and perhaps get that energy boost while others are fading?

“I was positioned at the front so I decided to bring the girls in, which was good,” Gubecka said. “It’s just a bit of Powerade and a couple caffeinated things in it to make sure I’m alert and awake and can get to the end very well.”

EVERY U.S. MEDAL AT THE RIO OLYMPICS