Galen Rupp and Jordan Hasay have flown from Oregon to the Czech Republic to race half marathons on Saturday--16 days before they race the Boston Marathon.

(You can watch Rupp's and Hasay's races at the Sportisimo Prague Half Marathon live on FloTrack in North America, beginning at 1 AM Pacific/4 AM Eastern. If you're watching the Stanford Invitational anyway, the races begin about an hour and 20 minutes after the Stanford men's 10K.)

There was a half marathon in New York City two weekends ago; there was a 15K in Florida three weekends ago (which Hasay won). The point here is, there are plenty of under-distance racing opportunities that required less taxing travel and provided more recovery time before Boston. But in coordination with their coach, Alberto Salazar, who is a fanatic planner, they chose this one in Prague. Why?

One answer is that the course is extremely fast, which definitely puts the men's American record in jeopardy and quietly could scare the women's. In 2015, three men broke 60:00, and last year, five men did. At 59:43, Ryan Hall is the only American man ever to do so.

Last year's women's race saw Viola Jepchumba and Worknesh Degafa become the Nos. 4 and 10 fastest performers in world history, respectively; Hasay's 68:40 PR would have placed her fourth last year and third the year before.

Rupp ran 60:30 ​six years ago ​(though the NYC half course was not record-legal then) and 61:20 in December 2015 to get his Trials qualifier. His 26:44 10K PR by any conversion tool is worth a sub-59:00 half; the IAAF scoring tables have it at 58:37. And Hasay ran 68:40 in nearly 100 percent humidity in her debut in Houston in January and said post-race that she thought she could've run 68:00.

Conditions in Prague are forecasted to be light winds and temperatures in the mid-50s. If that holds up, the U.S. all-time lists could be in for a beating.

Men

Rank	Athlete	Time
1	Ryan Hall	59:43
2	Dathan Ritzenhein	60:00
3	Diego Estrada	60:51
4	Mark Curp	60:55
5	Meb Keflezighi	61:00
6	Abdi Abdirahman	61:07
7	Khalid Khannouchi	61:17
8	Galen Rupp	61:20
9	Tim Ritchie	61:23
10	Luke Puskedra	61:29

Women

Rank	Athlete	Time
1	Deena Kastor	67:34
2	Molly Huddle	67:41
3	Kara Goucher	68:05
4	Emily Sisson	68:21
5	Amy Cragg	68:27
6	Shalane Flanagan	68:31
7	Joan Samuelso	68:34
8	Jordan Hasay	68:40
9	Cathy O'Brien	69:39
10	Kim Conley	69:44

The competition

Here's yet another reason to believe that Rupp and Hasay are going to run historically fast on Saturday morning: All they likely have to do is hang in the pack. The men's field is highlighted by four sub-60:00 half marathoners, led by Barselius Kipyego at 59:15. But the biggest non-Rupp name in the field might be Tamirat Tola, who won bronze in the Olympic 10K and ran 2:04:11 to become the ninth fastest marathoner of all time in January.

The women's field is even deeper. Hasay's 68:40 is the fifth-fastest PR in the field, but Violah Jepchumba (65:51) and Joyciline Jepkosgei (66:08) are the fourth- and seventh-fastest runners in the history of the event. Jepchumba ran her time in Prague last year; you come here to run fast. 

If Rupp smashes or even scares the American record on Saturday and then performs well in Boston 16 days later, it'll be only the most recent thing he did that smashed conventional wisdom. It's widely held that a fast half marathon right before a full marathon does not portend well for the full, and for good reason--the two races employ totally different physiological systems. As a friend is fond of saying, the half marathon is the same distance from the marathon--13.1 miles--as it is from the 200 meters.

But the typical rules have not applied in Rupp's career. He is the eighth-fastest indoor miler in world history; as far as I can tell, none of the other top 10 indoor milers ever have even finished a marathon. Rupp has an Olympic bronze medal in the marathon. And he didn't win it the easy way; he won it eight days after racing a 10K on the track. At this point, it would be incredibly impressive but unsurprising if Rupp broke the half American record and finished in the top three in Boston less than three weeks apart.

The splits to watch

When you're tuning in (beginning at 4 AM Eastern, in North America), keep an eye on these splits for Rupp and Hasay. For Rupp, American record pace is 4:33.31 per mile. So that would put him at:

​Mile 1 4:33
​Mile 2 9:06
​Mile 3 13:39
​Mile 4 18:13
​Mile 5 22:46
Mile 6 27:19
Mile 7 31:53
Mile 8 36:26
Mile 9 40:59
Mile 10 45:33
Mile 11 50:06
Mile 12 54:39
Mile 13 59:13

For Hasay, there isn't one particular milestone to watch for Saturday. The American record pace (67:34) is 5:09 per mile; her PR (68:40) is 5:14. Right in between those two and what Hasay is likely aiming for, 68:00, is 5:11 pace.

​WATCH THE SPORTISMO PRAGUE HALF MARATHON LIVE ON FLOTRACK ON SATURDAY, APRIL 1, IN NORTH AMERICA AT 4 AM EASTERN