Defining the “song of the summer” is a fraught concept, with so many options from so many genres — but there’s no question that one of the top contenders of 2017 originated in Nashville.

Sam Hunt’s inescapable “Body Like a Back Road,” a two-minute-and-45-second earworm in which a narrator extols the physical virtues of his ladyfriend, shattered records last week after reaching 25 consecutive weeks on the top of the Billboard Hot Country Songs chart, the longest No. 1 streak in history. The previous record-holder was Florida Georgia Line’s “Cruise” in 2012, at 24 weeks, followed by Leroy Van Dyke’s “Walk On By” in 1961, at 19 weeks.

The chart, which has existed since 1958, measures radio play and sales, and in more recent years, streaming. Spotify and Pandora numbers probably gave a big boost to “Body Like a Back Road,” which is also the third most-downloaded song of any genre in 2017, selling approximately 1.4 million digital copies so far. The track also spent three weeks at No. 1 on country radio, a rare accomplishment in an era where hits are quickly shuffled off the top of the charts.

So, how did it happen?

Even Hunt’s three co-writers — Shane McAnally, Josh Osborne and Zach Crowell — still aren’t quite sure. (Hunt was unavailable to comment.) Crowell, also Hunt’s producer, said the song is “maybe 25 best-case scenarios at the same time”: perfect timing as it hits its peak in summer; a sound that fits on modern country radio; and satisfaction for Hunt’s fans who were craving new material, given that he has barely released any since his debut multiplatinum album, “Montevallo,” in 2014.

“The moons lined up in our favor … the world was really wanting to like Sam’s next song,” Crowell said.

Plus, he added, the song’s precise, pared-down lyrics were appealing. “I definitely think it’s simple,” he said. “And simple always wins. That’s one common thread from the beginning of music.”

Indeed, the song doesn’t mince words. Hunt briskly finishes off the verses and puts all the emphasis on the can’t-get-it-out-of-your-head chorus: “Body like a back road/driving with my eyes closed/I know every curve like the back of my hand.” But for a “simple” song, the writing process was complicated.

The track was born out of a songwriters’ trip in November 2016 to Charleston, S.C., as the four — who have written together for years — looked for inspiration outside of Nashville. One day, Hunt said, “I have an idea for a song, but I don’t know if you think it’s a cool idea.” He offered the title, “Body Like a Back Road.” According to Osborne, the group was immediately intrigued.

“We were like, ‘Yes, we want to write that,’ ” Osborne said. “It just sounded like a hit country song.”

The four of them spent hours working on the lyrics, and although the chorus stayed much the same throughout the process, the verses went through many iterations. First, they had too many references to the road, so it felt overwritten. Then they took them out, and the song was too loose. They rewrote some more.

Finally, they left Charleston thinking the song was finished. However, a couple of months later, Hunt still thought the lyrics needed to be polished, and they went back to work.

The hardest part was making it sound conversational, a frequent ingredient in Hunt’s music; he will occasionally break into spoken word. Osborne said they cracked the code when Hunt came up with the line, “Had to get her number, took me like six weeks.” It might sound silly, but the lyric indicates a longer story in a few words, and listeners might be able to relate.

“Sam has the advantage of going out on stage and performing these songs, so he has the viewpoint of what people are going to respond to. So sometimes that’s hard for us, because we’re trying to write these definitive lines that people will go, ‘How did they think of that?’ ” McAnally said. “Honestly, this song does that, but in a different way. That’s how I feel when I hear it, I’m like, ‘The breeze and the birds!’ I mean, it must have taken us nine hours of actual songwriting work to ever come to that line. It’s just a different beast.”

Eventually, they perfected the lyrics. Crowell produced the track, and upon its release in February, “Body Like a Back Road” rocketed up the charts — and just kept going. While Hunt’s affinity for pop and R&B can be polarizing, his success proves that there’s an appetite for his style of music. He’s the genre’s next hope for a pop crossover sensation.

Osborne said he has received a hugely positive response from the writing community in Nashville, and the song’s breakthrough is a good reminder of the benefits of lighter songs, even if the instinct for Nashville writers is to dig deeper. (Or, in his words, the goal is often to “write a song where I play it at the Bluebird and the crowd cries.”)

“But there’s something to be said to be part of a song that’s part of someone’s summer vacation, or when they’re jamming out at the lake,” Osborne said. “We talk so much as songwriters that we want to make people feel something – so many times we forget that ‘happy’ is something that people feel, too.”

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