Certain Americans — you know the type — take physical fitness far too seriously. These people probably don’t spend a lot of time on the couch watching television; they’re too busy training for the next Ironman or Spartan Death Race.

But two shows that seem aimed directly at them begin in the next few days. One will make them say, “Hey, I want to try that.” The other might cause them to convert to couch potatoism.

“Steve Austin’s Broken Skull Challenge,” which had its premiere Sunday night on CMT, is the inviting one. Austin, the actor and former professional wrestler, is the growly host of a competition show that pits impossibly fit contestants against one another and against an obstacle course called the Skullbuster.

It’s a 10-obstacle, half-mile course that is both intimidating and irresistible. Anyone who has run a Tough Mudder or other extreme race — or even some people who only dream of doing so — will be on the phone to CMT, asking for a chance. There is rope-swinging. There is belly-crawling. There is wall-climbing. All under what looks to be a very hot sun.

If “Broken Skull Challenge” makes it seem as if getting in shape might be fun, “American Muscle,” which begins Wednesday on the Discovery Channel, does the opposite. The show chronicles the goings-on at the Barwis Methods Training Center near Detroit, frequented by professional athletes, people who want to be professionals and others. Mike Barwis presides, and, from the look of things, if you’re given a choice between doing his workout and being tortured by Jack Bauer of “24,” Jack is the less stressful option.

“I’m going to show you my own special breed of hell,” Barwis, who is even growlier than Austin, says, describing a regimen called hypertrophy. It’s a program that aims to build muscle mass, and a frightfully unforgiving one.

Among the athletes who turn up in the premiere is Richard Sherman, the Seattle Seahawks cornerback, whose comments after a playoff game last year caused a ruckus. But the real stars here are pain and suffering.