You wince for them already, the breakable souls for the Kansas City Chiefs who have to try to tackle Derrick Henry. The most imposing force left in these NFL playoffs is Henry when he dents a line. By his fourth step, the 6-foot-3, ­247-pound Tennessee Titans running back is moving at an estimated 21 mph. The defenders who meet that will be promptly and forcibly reminded of what Jim Brown once said: “Make sure when anyone tackles you, he remembers how much it hurts.”

Chiefs safety Tyrann Mathieu remembers. He tackled Henry earlier this season and thought he had broken his jaw. He told CBS it was like hitting solid rock. Baltimore Ravens all-pro cornerback Marlon Humphrey felt Henry in their upset loss to the Titans in the AFC divisional round last week. He recommends that anyone who wants to try it go to the weight room and “get an extra lift in.”

So far, absolutely no one has found a way to slow down Henry’s demolishing forward tilt, much less stop him. He enters Sunday’s AFC championship game with the momentum of a runaway bus, having run for more than 180 yards in three straight games, the first man in NFL history to do so. Hit him high? He gets you with that stiff arm, long and forceful as a horseman’s lance, such as the one he gave Earl Thomas of the Ravens, saying, “Good to see you, Earl; let’s do this again,” before he left him spinning in the turf. Or sometimes he’ll just shoulder three or four guys and “carry you for about five more yards,” said Chiefs linebacker Anthony Hitchens, before he sheds you and leaves you crumpled on the field like a ball of lint.

“He’s like one of those guys the kids create on Madden,” Ravens defensive coordinator Don “Wink” Martindale said. “You shouldn’t be able to be that big and run like he does.”

All things considered, the Chiefs said they have decided to “kill the engine” that is Henry by going low. “You’ve just got to take his legs out,” Hitchens said. “Hit him in his thighs and chop him down.”

The problem with that, Hitchens pointed out, is that those thighs are as heavy as cannonballs. Another problem is Henry’s offensive linemen, a “mean and nasty” crew according to Mathieu, who make it hard to get at his legs. And then there is the fact that Henry simply likes to hit — according to Pro Football Focus, almost 85 percent of his yardage comes after contact.

“We want it gritty,” Henry said after dispatching the New England Patriots. “We want it dirty.”

Maybe the best idea for how to bring down Henry came from cornerback Vernon Hargreaves III, back when he was in college at Florida and Henry was Alabama’s Heisman Trophy winner.

“Just hold on,” Hargreaves said then, “and wait for the team to get there.”

Henry’s development into the X-factor this postseason has laid waste to defensive strategy. There is nothing cute about what Henry and the Titans do to defenders. They just destroy your will. Back in Week 10, when the Titans beat the Chiefs, 35-32, behind 188 yards from Henry, Coach Mike Vrabel described their endgame plan. It was simply this: “Pound out 10-, 11-, 12-yard runs, and then ultimately watch those guys leave the game, or be on a knee, or be tired, or be banged up, and then walk into the end zone,” Vrabel said.

You can see the result of all that repetitive battering, how a team breaks, in Henry’s numbers. He averages a whopping 6.6 yards per carry in the third quarter.

“Second-half football, he takes off,” Mathieu said. “So we got to be well-rested, hydrated in order to kind of finish the game, try to compete against him and slow him down when it matters the most in the fourth quarter — four-minute drives, six-minute drives, seven minutes left.”

Defenses fall under the illusion that Henry actually gets stronger as the game wears on. But as former Alabama teammate Jake Coker has said, it’s more a case of: “He stays the same; everybody else changes.”

Former Michigan State defensive coordinator Harlon Barnett, whose team faced Henry in the 2015 College Football Playoff, described it this way: “You get tired of hitting that big back,” he said. “Boom. Again. Here he comes again. Boom. Again and again and again. And so you have to have the mental toughness to be able to say: ‘Hold on. We’re going to hold up, and we’re going to keep smacking him. Keep hitting him.’ ”

That’s if you can get your hands on him. Compounding his weightiness and his speed — 4.5 seconds in the 40-yard dash — is his ability to cut back and make defenders miss in space. And as if those traits weren’t enough to deal with, there is his long stride. At 6-foot-3, he eats up the yard lines as though his legs are hungry for dirt.

Someone at Alabama once measured that stride. In full lope, Henry covers 7½ feet per step. Think about that for a second: That’s 2½ yards per stride. It’s 10 yards in just four steps. “If we can get him into his fourth or fifth step, we feel very confident in his ability and our ability to gain meaningful yards,” Vrabel said. And once he breaks a tackle, he’s gone. On 23 occasions this season, he has burst upfield for 15 yards or longer, most in the league. 

“He doesn’t get caught much,” Patriots Coach Bill Belichick observed.

Finally, there is Henry’s capacity for a daunting workload. He has carried the ball 96 times in his past three games, a scarcely believable rate in this era of balanced offense. But for him, it’s normal. Back in high school in Yulee, Fla., he regularly carried 40 or more times per game, and the trend continued at Alabama.

Most coaches generally prefer not to work a back more than 20 or 25 times for fear of compromising fumbles. But late in his Heisman season at Alabama, he carried 46 times against Auburn, followed by 44 carries against Florida a week later. The coaches would muse about whether he needed a rest. “But you see the body language,” Alabama offensive coordinator Lane Kiffin said then. They realized Henry liked it.

“I get in a rhythm the more carries I get,” he said.

His endurance prompted a Southwest Airlines Twitter handler to have a little fun this week. Asked whether the airline planned any extra flights between Nashville and Kansas City, the airline agent wrote:

“Though we don’t have any plans to add additional routes, we are pretty sure that Derrick Henry would just put you on his back and run you there.”

For more by Sally Jenkins, visit washingtonpost.com/jenkins.